,,transcriber',s ,,note3 ,spelling maintained as closely as possible to the original document1 while obvious typos have been corrected4 ,emdashes in original text for negative temperatures changed to minus signs to standardize temperatures4 ,,climatic ,,changes ,,their ,,nature ,,and ,,causes ,,published ,,on ,,the ,,foundation ,,established ,,in ,,memory ,,of ,,theodore ,l4 ,,glasgow ,,other ,,books ,,by ,,the ,,same ,,authors ,,ellsworth ,,huntington ,a4 ,four books showing the development of knowledge as to ,historical ,pulsations of ,climate4 ,the ,pulse of ,asia4 ,boston1 #aijg4 ,explorations in ,turkestan4 ,expedition of #aijc4 ,washington1 #aije4 ,palestine and ,its ,transformation4 ,boston1 #aiaa4 ,the ,climatic ,factor1 as ,illustrated in ,arid ,america4 ,washington1 #aiad4 ,b4 ,two books illustrating the effect of climate on man4 ,civilization and ,climate4 ,new ,haven1 #aiae4 ,world ,power and ,evolution4 ,new ,haven1 #aiai4 ,c4 ,four books illustrating the general principles of ,geography4 ,asia3 ,a ,geography ,reader4 ,chicago1 #aiab4 ,the ,red ,man's ,continent4 ,new ,haven1 #aiai4 ,principles of ,human ,geography 7with ,s4 ,w4 ,cushing74 ,new ,york1 #aibj4 ,business ,geography 7with ,f4 ,e4 ,williams74 ,new ,york1 #aibb4 ,d4 ,a companion to the present volume4 ,earth and ,sun3 ,an ,hypothesis of ,weather and ,sunspots4 ,new ,haven4 ,in press4 ,,stephen ,,sargent ,,visher ,geography1 ,geology and ,biology of ,southern ,dakota4 ,vermilion1 #aiab4 ,the ,biology of ,northwestern ,south ,dakota4 ,vermilion1 #aiad4 ,the ,geography of ,south ,dakota4 ,vermilion1 #aiah4 ,handbook of the ,geology of ,indiana 7with others74 ,indianapolis1 #aibb4 ,hurricanes of ,australia and the ,south ,pacific4 ,melbourne1 #aibb4 ,,climatic ,,changes ,,their ,,nature ,,and ,,causes ,,by ,,ellsworth ,,huntington ,research ,associate in ,geography in ,yale ,university ,,and ,,stephen ,,sargent ,,visher ,associate ,professor of ,geology in ,indiana ,university ,illustration ,,new ,,haven ,,yale ,,university ,,press ,,london3 ,,humphrey ,,milford3 ,,oxford ,,university ,,press ,,mdccccxxii ,,copyright #aibb ,,by ,,yale ,,university ,,press ,published #aibb4 ,,the ,,theodore ,l4 ,,glasgow ,,memorial ,,publication ,,fund ,the present volume is the fifth work published by the ,yale ,university ,press on the ,theodore ,l4 ,glasgow ,memorial ,publication ,fund4 ,this foundation was established ,september #ag1 #aiah1 by an anonymous gift to ,yale ,university in memory of ,flight ,sub-,lieutenant ,theodore ,l4 ,glasgow1 ,r4,n4 ,he was born in ,montreal1 ,canada1 and was educated at the ,university of ,toronto ,schools and at the ,royal ,military ,college1 ,kingston4 ,in ,august1 #aiaf1 he entered the ,royal ,naval ,air ,service and in ,july1 #aiag1 went to ,france with the ,tenth ,squadron attached to the ,twenty-second ,wing of the ,royal ,flying ,corps4 ,a month later1 ,august #ai1 #aiag1 he was killed in action on the ,ypres front4 ,,to ,,thomas ,,chrowder ,,chamberlin ,,of ,,the ,,university ,,of ,,chicago ,,whose ,,clear ,,and ,,masterly ,,discussion ,,of ,,the ,,great ,,problems ,,of ,,terrestrial ,,evolution ,,has ,,been ,,one ,,of ,,the ,,most ,,inspiring ,,factors ,,in ,,the ,,writing ,,of ,,this ,,book ,there is a toy1 which ,i have heard1 and ,i would not have it given over1 but waited upon a little4 ,they say it is observed in the ,low ,countries 7,i know not in what part71 that every five and thirty years the same kind and suit of years and weathers comes about again2 as great frosts1 great wet1 great droughts1 warm winters1 summers with little heat1 and the like1 and they call it the prime2 it is a thing ,i do the rather mention1 because1 computing backwards1 ,i have found some concurrence4 ,,francis ,,bacon ,,preface ,unity is perhaps the keynote of modern science4 ,this means unity in time1 for the present is but the outgrowth of the past1 and the future of the present4 ,it means unity of process1 for there seems to be no sharp dividing line between organic and inorganic1 physical and mental1 mental and spiritual4 ,and the unity of modern science means also a growing tendency toward cooeperation1 so that by working together scientists discover much that would else have remained hid4 ,this book illustrates the modern trend toward unity in all of these ways4 ,first1 it is a companion volume to ,earth and ,sun4 ,that volume is a discussion of the causes of weather1 but a consideration of the weather of the present almost inevitably leads to a study of the climate of the past4 ,hence the two books were written originally as one1 and were only separated from considerations of convenience4 ,second1 the unity of nature is so great that when a subject such as climatic changes is considered1 it is almost impossible to avoid other subjects1 such as the movements of the earth's crust4 ,hence this book not only discusses climatic changes1 but considers the causes of earthquakes and attempts to show how climatic changes may be related to great geological revolutions in the form1 location1 and altitude of the lands4 ,thus the book has a direct bearing on all the main physical factors which have molded the evolution of organic life1 including man4 ,in the third place1 this volume illustrates the unity of modern science because it is preeminently a cooeperative product4 ,not only have the two authors shared in its production1 but several of the ,yale ,faculty have also cooeperated4 ,from the geological standpoint1 ,professor ,charles ,schuchert has read the entire manuscript in its final form as well as parts at various stages4 ,he has helped not only by criticisms1 suggestions1 and facts1 but by paragraphs ready for the printer4 ,in the same way in the domain of physics1 ,professor ,leigh ,page has repeatedly taken time to assist1 and either in writing or by word of mouth has contributed many pages4 ,in astronomy1 the same cordial cooeperation has come with equal readiness from ,professor ,frank ,schlesinger4 ,professors ,schuchert1 ,schlesinger1 and ,page have contributed so materially that they are almost co-authors of the volume4 ,in mathematics1 ,professor ,ernest ,w4 ,brown has been similarly helpful1 having read and criticised the entire book4 ,in certain chemical problems1 ,professor ,harry ,w4 ,foote has been our main reliance4 ,the advice and suggestions of these men have frequently prevented errors1 and have again and again started new and profitable lines of thought4 ,if we have made mistakes1 it has been because we have not profited sufficiently by their cooeperation4 ,if the main hypothesis of this book proves sound1 it is largely because it has been built up in constant consultation with men who look at the problem from different points of vision4 ,our appreciation of their generous and unstinted cooeperation is much deeper than would appear from this brief paragraph4 ,outside the ,yale ,faculty we have received equally cordial assistance4 ,professor ,t4 ,c4 ,chamberlin of the ,university of ,chicago1 to whom1 with his permission1 we take great pleasure in dedicating this volume1 has read the entire proof and has made many helpful suggestions4 ,we cannot speak too warmly of our appreciation not only of this1 but of the way his work has served for years as an inspiration in the preliminary work of gathering data for this volume4 ,professor ,harlow ,shapley of ,harvard ,university has contributed materially to the chapter on the sun and its journey through space2 ,professor ,andrew ,e4 ,douglass of the ,university of ,arizona has put at our disposal some of his unpublished results2 ,professors ,s4 ,b4 ,woodworth and ,reginald ,a4 ,daly1 and ,mr4 ,robert ,w4 ,sayles of ,harvard1 and ,professor ,henry ,f4 ,reid of ,johns ,hopkins have suggested new facts and sources of information2 ,professor ,e4 ,r4 ,cumings of ,indiana ,university has critically read the entire proof2 conversations with ,professor ,john ,p4 ,buwalda of the ,university of ,california while he was teaching at ,yale make him another real contributor2 and ,mr4 ,wayland ,williams has contributed the interesting quotation from ,bacon on page x of this book4 ,miss ,edith ,s4 ,russell has taken great pains in preparing the manuscript and in suggesting many changes that make for clearness4 ,many others have also helped1 but it is impossible to make due acknowledgment because such contributions have become so thoroughly a part of the mental background of the book that their source is no longer distinct in the minds of the authors4 ,the division of labor between the two authors has not followed any set rules4 ,both have had a hand in all parts of the book4 ,the main draft of ,chapters ,,vii1 ,,viii1 ,,ix1 ,,xi1 and ,,xiii was written by the junior author2 his contributions are also especially numerous in ,chapters ,x and ,,xv2 the rest of the book was written originally by the senior author4 ,,contents ,,page ,i4 ,the ,uniformity of ,climate #a ,,ii4 ,the ,variability of ,climate #af ,,iii4 ,hypotheses of ,climatic ,change #cc ,,iv4 ,the ,solar ,cyclonic ,hypothesis #ea ,v4 ,the ,climate of ,history #fd ,,vi4 ,the ,climatic ,stress of the ,fourteenth ,century #ih ,,vii4 ,glaciation ,according to the ,solar ,cyclonic ,hypothesis #aaj ,,viii4 ,some ,problems of ,glacial ,periods #acj ,,ix4 ,the ,origin of ,loess #aee ,x4 ,causes of ,mild ,geological ,climates #aff ,,xi4 ,terrestrial ,causes of ,climatic ,changes #ahh ,,xii4 ,post-,glacial ,crustal ,movements and ,climatic ,changes #bae ,,xiii4 ,the ,changing ,composition of ,oceans and ,atmosphere #bbc ,,xiv4 ,the ,effect of ,other ,bodies on the ,sun #bdb ,,xv4 ,the ,sun's ,journey through ,space #bfd ,,xvi4 ,the ,earth's ,crust and the ,sun #bhe ,,list ,,of ,,illustrations ,,page ,fig4 #a4 ,climatic changes and mountain building #be ,fig4 #b4 ,storminess at sunspot maxima vs4 minima #ed ,fig4 #c4 ,relative rainfall at times of increasing and decreasing sunspots #eh1 #ei ,fig4 #d4 ,changes of climate in ,california and in western and central ,asia #ge ,fig4 #e4 ,changes in ,california climate for #bjjj years1 as measured by growth of ,sequoia trees #gg ,fig4 #f4 ,distribution of ,pleistocene ice sheets #abc ,fig4 #g4 ,permian geography and glaciation #ade ,fig4 #h4 ,effect of diminution of storms on movement of water #age ,fig4 #i4 ,cretaceous ,paleogeography #bja ,fig4 #aj4 ,climatic changes of #adj1jjj years as inferred from the stars #bgi ,fig4 #aa4 ,sunspot curve showing cycles1 #agej to #aibj #bhc ,fig4 #ab4 ,seasonal distribution of earthquakes #bii ,fig4 #ac4 ,wandering of the pole from #ahij to #ahih #cjc ,,tables ,,page #a4 ,the ,geological ,time ,table #e #b4 ,types of ,climatic ,sequence #af #c4 ,correlation ,coefficients between ,rainfall and ,growth of ,sequoias in ,california #hj #d4 ,correlation ,coefficients between ,rainfall ,records in ,california and ,jerusalem #hd #e4 ,theoretical ,probability of ,stellar ,approaches #bfj #f4 ,thirty-,eight ,stars ,having ,largest ,known ,parallaxes #bgf1 #bgg #g4 ,destructive ,earthquakes from #ahjj to #ahii ,compared with ,sunspots #bhi #h4 ,seasonal ,march of ,earthquakes #bie #i4 ,deflection of ,path of ,pole ,compared with ,earthquakes #cje #aj4 ,earthquakes in #aijc to #aijh ,compared with ,departures of the ,projected ,curve of the ,earth's ,axis from the ,eulerian ,position #cjf ,,chapter ,i ,,the ,,uniformity ,,of ,,climate ,the role of climate in the life of today suggests its importance in the past and in the future4 ,no human being can escape from the fact that his food1 clothing1 shelter1 recreation1 occupation1 health1 and energy are all profoundly influenced by his climatic surroundings4 ,a change of season brings in its train some alteration in practically every phase of human activity4 ,animals are influenced by climate even more than man1 for they have not developed artificial means of protecting themselves4 ,even so hardy a creature as the dog becomes notably different with a change of climate4 ,the thick-haired husky of the ,eskimos has outwardly little in common with the small and almost hairless canines that grovel under foot in ,mexico4 ,plants are even more sensitive than animals and men4 ,scarcely a single species can flourish permanently in regions which differ more than #bj deg4,c4 in average yearly temperature1 and for most the limit of successful growth is #aj deg44#a ,so far as we yet know every living species of plant and animal1 including man1 thrives best under definite and limited conditions of temperature1 humidity1 and sunshine1 and of the composition and movement of the atmosphere or water in which it lives4 ,any departure beyond the limits means lessened efficiency1 and in the long run a lower rate of reproduction and a tendency toward changes in specific characteristics4 ,any great departure means suffering or death for the individual and destruction for the species4 ,since climate has so profound an influence on life today1 it has presumably been equally potent at other times4 ,therefore few scientific questions are more important than how and why the earth's climate has varied in the past1 and what changes it is likely to undergo in the future4 ,this book sets forth what appear to be the chief reasons for climatic variations during historic and geologic times4 ,it assumes that causes which can now be observed in operation1 as explained in a companion volume entitled ,earth and ,sun1 and in such books as ,humphreys' ,physics of the ,air1 should be carefully studied before less obvious causes are appealed to4 ,it also assumes that these same causes will continue to operate1 and are the basis of all valid predictions as to the weather or climate of the future4 ,in our analysis of climatic variations1 we may well begin by inquiring how the earth's climate has varied during geological history4 ,such an inquiry discloses three great tendencies1 which to the superficial view seem contradictory4 ,all1 however1 have a similar effect in providing conditions under which organic evolution is able to make progress4 ,the first tendency is toward uniformity1 a uniformity so pronounced and of such vast duration as to stagger the imagination4 ,superposed upon this there seems to be a tendency toward complexity4 ,during the greater part of geological history the earth's climate appears to have been relatively monotonous1 both from place to place and from season to season2 but since the ,miocene the rule has been diversity and complexity1 a condition highly favorable to organic evolution4 ,finally1 the uniformity of the vast eons of the past and the tendency toward complexity are broken by pulsatory changes1 first in one direction and then in another4 ,to our limited human vision some of the changes1 such as glacial periods1 seem to be waves of enormous proportions1 but compared with the possibilities of the universe they are merely as the ripples made by a summer zephyr4 ,the uniformity of the earth's climate throughout the vast stretches of geological time can best be realized by comparing the range of temperature on the earth during that period with the possible range as shown in the entire solar system4 ,as may be seen in ,table #a1 the geological record opens with the ,archeozoic era1 or ,age of ,unicellular ,life1 as it is sometimes called1 for the preceding cosmic time has left no record that can yet be read4 ,practically no geologists now believe that the beginning of the ,archeozoic was less than one hundred million years ago2 and since the discovery of the peculiar properties of radium many of the best students do not hesitate to say a billion or a billion and a half4#b ,even in the ,archeozoic the rocks testify to a climate seemingly not greatly different from that of the average of geologic time4 ,the earth's surface was then apparently cool enough so that it was covered with oceans and warm enough so that the water teemed with microscopic life4 ,the air must have been charged with water vapor and with carbon dioxide1 for otherwise there seems to be no possible way of explaining the formation of mudstones and sandstones1 limestones of vast thickness1 carbonaceous shales1 graphites1 and iron ores4#c ,although the ,archeozoic has yielded no generally admitted fossils1 yet what seem to be massive algae and sponges have been found in ,canada4 ,on the other hand1 abundant life is believed to have been present in the oceans1 for by no other known means would it be possible to take from the air the vast quantities of carbon that now form carbonaceous shales and graphite4 ,in the next geologic era1 the ,proterozoic1 the researches of ,walcott have shown that besides the marine algae there must have been many other kinds of life4 ,the ,proterozoic fossils thus far discovered include not only microscopic radiolarians such as still form the red ooze of the deepest ocean floors1 but the much more significant tubes of annelids or worms4 ,the presence of the annelids1 which are relatively high in the scale of organization1 is generally taken to mean that more lowly forms of animals such as coelenterates and probably even the mollusca and primitive arthropods must already have been evolved4 ,that there were many kinds of marine invertebrates living in the later ,proterozoic is indicated by the highly varied life and more especially the trilobites found in the oldest ,cambrian strata of the next succeeding period4 ,in fact the ,cambrian has sponges1 primitive corals1 a great variety of brachiopods1 the beginnings of gastropods1 a wonderful array of trilobites1 and other lowly forms of arthropods4 ,since1 under the postulate of evolution1 the life of that time forms an unbroken sequence with that of the present1 and since many of the early forms differ only in minor details from those of today1 we infer that the climate then was not very different from that of today4 ,the same line of reasoning leads to the conclusion that even in the middle of the ,proterozoic1 when multicellular marine animals must already have been common1 the climate of the earth had already for an enormous period been such that all the lower types of oceanic invertebrates had already evolved4 ,,table #a ,,the ,,geological ,,time ,,table#d ,,cosmic ,,time ,,formative ,,era4 ,birth and growth of the earth4 ,beginnings of the atmosphere1 hydrosphere1 continental platforms1 oceanic basins1 and possibly of life4 ,no known geological record4 ,,geologic ,,time ,,archeozoic ,,era4 ,origin of simplest life4 ,,proterozoic ,,era4 ,age of invertebrate origins4 ,an early and a late ice age1 with one or more additional ones indicated4 ,,paleozoic ,,era4 ,age of primitive vertebrate dominance4 ,cambrian ,period4 ,first abundance of marine animals and dominance of trilobites4 ,ordovician ,period4 ,first known fresh-water fishes4 ,silurian ,period4 ,first known land plants4 ,devonian ,period4 ,first known amphibians4 ,table ,mountain ice age4 ,mississippian ,period4 ,rise of marine fishes 7sharks74 ,pennsylvanian ,period4 ,rise of insects and first period of marked coal accumulation4 ,permian ,period4 ,rise of reptiles4 ,another great ice age4 ,,mesozoic ,,era4 ,age of reptile dominance4 ,triassic ,period4 ,rise of dinosaurs4 ,the period closes with a cool climate4 ,jurassic ,period4 ,rise of birds and flying reptiles4 ,comanchean ,period4 ,rise of flowering plants and higher insects4 ,cretaceous ,period4 ,rise of archaic or primitive mammalia4 ,,cenozoic ,,era4 ,age of mammal dominance4 ,early ,cenozoic or ,eocene and ,oligocene time4 ,rise of higher mammals4 ,glaciers in early ,eocene of the ,laramide ,mountains4 ,late ,cenozoic or ,miocene and ,pliocene time4 ,transformation of ape like animals into man4 ,glacial or ,pleistocene time4 ,last great ice age4 ,,present ,,time ,,psychozoic ,,era4 ,age of man or age of reason4 ,includes the present or ,recent time1 estimated to be probably less than #cj1jjj years4 ,moreover1 they could live in most latitudes1 for the indirect evidences of life in the ,archeozoic and ,proterozoic rocks are widely distributed4 ,thus it appears that at an almost incredibly early period1 perhaps many hundred million years ago1 the earth's climate differed only a little from that of the present4 ,the extreme limits of temperature beyond which the climate of geological times cannot have departed can be approximately determined4 ,today the warmest parts of the ocean have an average temperature of about #cj deg4,c4 on the surface4 ,only a few forms of life live where the average temperature is much higher than this4 ,in deserts1 to be sure1 some highly organized plants and animals can for a short time endure a temperature as high as #ge deg4,c4 7#afg deg4,f474 ,in certain hot springs1 some of the lowest unicellular plant forms exist in water which is only a little below the boiling point4 ,more complex forms1 however1 such as sponges1 worms1 and all the higher plants and animals1 seem to be unable to live either in water or air where the temperature averages above #de deg4,c4 7#aac deg4,f47 for any great length of time and it is doubtful whether they can thrive permanently even at that temperature4 ,the obvious unity of life for hundreds of millions of years and its presence at all times in middle latitudes so far as we can tell seem to indicate that since the beginning of marine life the temperature of the oceans cannot have averaged much above #ej deg4,c4 even in the warmest portions4 ,this is putting the limit too high rather than too low1 but even so the warmest parts of the earth can scarcely have averaged much more than #bj deg4 warmer than at present4 ,turning to the other extreme1 we may inquire how much colder than now the earth's surface may have been since life first appeared4 ,proterozoic fossils have been found in places where the present average temperature approaches #j deg4,c4 ,if those places should be colder than now by #cj deg4,c41 or more1 the drop in temperature at the equator would almost certainly be still greater1 and the seas everywhere would be permanently frozen4 ,thus life would be impossible4 ,since the contrasts between summer and winter1 and between the poles and the equator seem generally to have been less in the past than at present1 the range through which the mean temperature of the earth as a whole could vary without utterly destroying life was apparently less than would now be the case4 ,these considerations make it fairly certain that for at least several hundred million years the average temperature of the earth's surface has never varied more than perhaps #cj deg4,c4 above or below the present level4 ,even this range of #fj deg4,c4 7#ajh deg4,f47 may be double or triple the range that has actually occurred4 ,that the temperature has not passed beyond certain narrow limits1 whatever their exact degree1 is clear from the fact that if it had done so1 all the higher forms of life would have been destroyed4 ,certain of the lowest unicellular forms might indeed have persisted1 for when dormant they can stand great extremes of dry heat and of cold for a long time4 ,even so1 evolution would have had to begin almost anew4 ,the supposition that such a thing has happened is untenable1 for there is no hint of any complete break in the record of life during geological times1--no sudden disappearance of the higher organisms followed by a long period with no signs of life other than indirect evidence such as occurs in the ,archeozoic4 ,a change of #fj deg4,c4 or even of #bj deg4 in the average temperature of the earth's surface may seem large when viewed from the limited standpoint of terrestrial experience4 ,viewed1 however1 from the standpoint of cosmic evolution1 or even of the solar system1 it seems a mere trifle4 ,consider the possibilities4 ,the temperature of empty space is the absolute zero1 or -#bgc deg4,c4 ,to this temperature all matter must fall1 provided it exists long enough and is not appreciably heated by collisions or by radiation4 ,at the other extreme lies the temperature of the stars4 ,as stars go1 our sun is only moderately hot1 but the temperature of its surface is calculated to be nearly #gjjj deg4,c41 while thousands of miles in the interior it may rise to #bj1jjj deg4 or #ajj1jjj deg4 or some other equally unknowable and incomprehensible figure4 ,between the limits of the absolute zero on the one hand1 and the interior of a sun or star on the other1 there is almost every conceivable possibility of temperature4 ,today the earth's surface averages not far from #ad deg4,c41 or #bhg deg4 above the absolute zero4 ,toward the interior1 the temperature in mines and deep wells rises about #a deg4,c4 for every #ajj meters4 ,at this rate it would be over #ejj deg4,c4 at a depth of ten miles1 and over #ejjj deg4 at #ajj miles4 ,let us confine ourselves to surface temperatures1 which are all that concern us in discussing climate4 ,it has been calculated by ,poynting#e that if a small sphere absorbed and re-radiated all the heat that fell upon it1 its temperature at the distance of ,mercury from the sun would average about #baj deg4,c42 at the distance of ,venus1 #he deg42 the earth #bg deg42 ,mars -#cj deg42 ,neptune -#bai deg44 ,a planet much nearer the sun than is ,mercury might be heated to a temperature of a thousand1 or even several thousand1 degrees1 while one beyond ,neptune would remain almost at absolute zero4 ,it is well within the range of possibility that the temperature of a planet's surface should be anywhere from near -#bgc deg4,c4 up to perhaps #ejjj deg4,c4 or more1 although the probability of low temperature is much greater than of high4 ,thus throughout the whole vast range of possibilities extending to perhaps #aj1jjj deg41 the earth claims only #fj deg4 at most1 or less than #a per cent4 ,this may be remarkable1 but what is far more remarkable is that the earth's range of #fj deg4 includes what seem to be the two most critical of all possible temperatures1 namely1 the freezing point of water1 #j deg4,c41 and the temperature where water can dissolve an amount of carbon dioxide equal to its own volume4 ,the most remarkable fact of all is that the earth has preserved its temperature within these narrow limits for a hundred million years1 or perchance a thousand million4 ,to appreciate the extraordinary significance of this last fact1 it is necessary to realize how extremely critical are the temperatures from about #j deg4 to #dj deg4,c41 and how difficult it is to find any good reason for a relatively uniform temperature through hundreds of millions of years4 ,since the dawn of geological time the earth's temperature has apparently always included the range from about the freezing point of water up to about the point where protoplasm begins to disintegrate4 ,henderson1 in ,the ,fitness of the ,environment1 rightly says that water is the most familiar and the most important of all things4 ,in many respects water and carbon dioxide form the most unique pair of substances in the whole realm of chemistry4 ,water has a greater tendency than any other known substance to remain within certain narrowly defined limits of temperature4 ,not only does it have a high specific heat1 so that much heat is needed to raise its temperature1 but on freezing it gives up more heat than any substance except ammonia1 while none of the common liquids approach it in the amount of additional heat required for conversion into vapor after the temperature of vaporization has been reached4 ,again1 water substance1 as the physicists call all forms of ,h#b,o1 is unique in that it not only contracts on melting1 but continues to contract until a temperature several degrees above its melting point is reached4 ,that fact has a vast importance in helping to keep the earth's surface at a uniform temperature4 ,if water were like most liquids1 the bottoms of all the oceans and even the entire body of water in most cases would be permanently frozen4 ,again1 as a solvent there is literally nothing to compare with water4 ,as ,henderson#f puts it3 ,nearly the whole science of chemistry has been built up around water and aqueous solution4 ,one of the most significant evidences of this is the variety of elements whose presence can be detected in sea water4 ,according to ,henderson they include hydrogen1 oxygen1 nitrogen1 carbon1 chlorine1 sodium1 magnesium1 sulphur1 phosphorus1 which are easily detected2 and also arsenic1 caesium1 gold1 lithium1 rubidium1 barium1 lead1 boron1 fluorine1 iron1 iodine1 bromine1 potassium1 cobalt1 copper1 manganese1 nickel1 silver1 silicon1 zinc1 aluminium1 calcium1 and strontium4 ,yet in spite of its marvelous power of solution1 water is chemically rather inert and relatively stable4 ,it dissolves all these elements and thousands of their compounds1 but still remains water and can easily be separated and purified4 ,another unique property of water is its power of ionizing dissolved substances1 a property which makes it possible to produce electric currents in batteries4 ,this leads to an almost infinite array of electro-chemical reactions which play an almost dominant role in the processes of life4 ,finally1 no common liquid except mercury equals water in its power of capillarity4 ,this fact is of enormous moment in biology1 most obviously in respect to the soil4 ,although carbon dioxide is far less familiar than water1 it is almost as important4 ,these two simple substances1 says ,henderson1 are the common source of every one of the complicated substances which are produced by living beings1 and they are the common end products of the wearing away of all the constituents of protoplasm1 and of the destruction of those materials which yield energy to the body4 ,one of the remarkable physical properties of carbon dioxide is its degree of solubility in water4 ,this quality varies enormously in different substances4 ,for example1 at ordinary pressures and temperatures1 water can absorb only about #e per cent of its own volume of oxygen1 while it can take up about #acjj times its own volume of ammonia4 ,now for carbon dioxide1 unlike most gases1 the volume that can be absorbed by water is nearly the same as the volume of the water4 ,the volumes vary1 however1 according to temperature1 being absolutely the same at a temperature of about #ae deg4,c4 or #ei deg4,f41 which is close to the ideal temperature for man's physical health and practically the same as the mean temperature of the earth's surface when all seasons are averaged together4 ,hence1 when water is in contact with air1 and equilibrium has been established1 the amount of free carbonic acid in a given volume of water is almost exactly equal to the amount in the adjacent air4 ,unlike oxygen1 hydrogen1 and nitrogen1 carbonic acid enters water freely2 unlike sulphurous oxide and ammonia1 it escapes freely from water4 ,thus the waters can never wash carbonic acid completely out of the air1 nor can the air keep it from the waters4 ,it is the one substance which thus1 in considerable quantities relative to its total amount1 everywhere accompanies water4 ,in earth1 air1 fire1 and water alike these two substances are always associated4 ,accordingly1 if water be the first primary constituent of the environment1 carbonic acid is inevitably the second1--because of its solubility possessing an equal mobility with water1 because of the reservoir of the atmosphere never to be depleted by chemical action in the oceans1 lakes1 and streams4 ,in truth1 so close is the association between these two substances that it is scarcely correct logically to separate them at all2 together they make up the real environment and they never part company4#g ,the complementary qualities of carbon dioxide and water are of supreme importance because these two are the only known substances which are able to form a vast series of complex compounds with highly varying chemical formulae4 ,no other known compounds can give off or take on atoms without being resolved back into their elements4 ,no others can thus change their form freely without losing their identity4 ,this power of change without destruction is the fundamental chemical characteristic of life1 for life demands complexity1 change1 and growth4 ,in order that water and carbon dioxide may combine to form the compounds on which life is based1 the water must be in the liquid form1 it must be able to dissolve carbon dioxide freely1 and the temperature must not be high enough to break up the highly complex and delicate compounds as soon as they are formed4 ,in other words1 the temperature must be above freezing1 while it must not rise higher than some rather indefinite point between #ej deg4,c4 and the boiling point1 where all water finally turns into vapor4 ,in the whole range of temperature1 so far as we know1 there is no other interval where any such complex reactions take place4 ,the temperature of the earth for hundreds of millions of years has remained firmly fixed within these limits4 ,the astonishing quality of the earth's uniformity of temperature becomes still more apparent when we consider the origin of the sun's heat4 ,what that origin is still remains a question of dispute4 ,the old ideas of a burning sun1 or of one that is simply losing an original supply of heat derived from some accident1 such as collision with another body1 were long ago abandoned4 ,the impact of a constant supply of meteors affords an almost equally unsatisfactory explanation4 ,moulton#h states that if the sun were struck by enough meteorites to keep up its heat1 the earth would almost certainly be struck by enough so that it would receive about half of #a per cent as much heat from them as from the sun4 ,this is millions of times more heat than is now received from meteors4 ,if the sun owes its heat to the impact of larger bodies at longer intervals1 the geological record should show a series of interruptions far more drastic than is actually the case4 ,it has also been supposed that the sun owes its heat to contraction4 ,if a gaseous body contracts it becomes warmer4 ,finally1 however1 it must become so dense that its rate of contraction diminishes and the process ceases4 ,under the sun's present condition of size and density a radial contraction of #abj feet per year would be enough to supply all the energy now radiated by that body4 ,this seems like a hopeful source of energy1 but ,kelvin calculated that twenty million years ago it was ineffective and ten million years hence it will be equally so4 ,moreover1 if this is the source of heat1 the amount of radiation from the sun would have to vary enormously4 ,twenty million years ago the sun would have extended nearly to the earth's orbit and would have been so tenuous that it would have emitted no more heat than some of the nebulae in space4 ,some millions of years later1 when the sun's radius was twice as great as at present1 that body would have emitted only one-fourth as much heat as now1 which would mean that on the earth's surface the theoretical temperature would have been #bjj deg4 below the present level4 ,this is utterly out of accord with the uniformity of climate shown by the geological record4 ,in the future1 if the sun's contraction is the only source of heat1 the sun can supply the present amount for only ten million years1 which would mean a change utterly unlike anything of which the geological record holds even the faintest hint4#i ,altogether the problem of how the sun can have remained so uniform and how the earth's atmosphere and other conditions can also have remained so uniform throughout hundreds of millions of years is one of the most puzzling in the whole realm of nature4 ,if appeal is taken to radioactivity and the breaking up of uranium into radium and helium1 conditions can be postulated which will give the required amount of energy4 ,such is also the case if it be supposed that there is some unknown process which may induce an atomic change like radioactivity in bodies which are now supposed to be stable elements4 ,in either case1 however1 there is as yet no satisfactory explanation of the uniformity of the earth's climate4 ,a hundred million or a thousand million years ago the temperature of the earth's surface was very much the same as now4 ,the earth had then presumably ceased to emit any great amount of heat1 if we may judge from the fact that its surface was cool enough so that great ice sheets could accumulate on low lands within #dj deg4 of the equator4 ,the atmosphere was apparently almost like that of today1 and was almost certainly not different enough to make up for any great divergence of the sun from its present condition4 ,we cannot escape the stupendous fact that in those remote times the sun must have been essentially the same as now1 or else that some utterly unknown factor is at work4 ,,footnotes3 ,footnote #a3 ,w4 ,a4 ,setchell3 ,the ,temperature ,interval in the ,geographical ,distribution of ,marine ,algae2 ,science1 ,vol4 #eb1 #aibj1 p4 #ahg4 ,footnote #b3 ,j4 ,barrell3 ,rhythms and the ,measurements of ,geologic ,time2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #bh1 ,dec41 #aiag1 pp4 #gde-ijd4 ,footnote #c3 ,pirsson and ,schuchert3 ,textbook of ,geology1 #aiae1 pp4 #ech-eej4 ,footnote #d3 ,from ,charles ,schuchert in ,the ,evolution of the ,earth and ,its ,inhabitants3 ,edited by ,r4 ,s4 ,lull1 ,new ,haven1 #aiah1 but with revisions by ,professor ,schuchert4 ,footnote #e3 ,j4 ,h4 ,poynting3 ,radiation in the ,solar ,system2 ,phil4 ,trans4 ,a1 #aijc1 #bjb1 p4 #ebe4 ,footnote #f3 ,l4 ,j4 ,henderson3 ,the ,fitness of the ,environment1 #aiac4 ,footnote #g3 ,henderson3 loc4 cit41 p4 #ach4 ,footnote #h3 ,f4 ,r4 ,moulton3 ,introduction to ,astronomy1 #aiaf4 ,footnote #i3 ,moulton3 loc4 cit4 ,,chapter ,,ii ,,the ,,variability ,,of ,,climate ,the variability of the earth's climate is almost as extraordinary as its uniformity4 ,this variability is made up partly of a long1 slow tendency in one direction and partly of innumerable cycles of every conceivable duration from days1 or even hours1 up to millions of years4 ,perhaps the easiest way to grasp the full complexity of the matter is to put the chief types of climatic sequence in the form of a table4 ---------------------------------------- ------------------- ,,table #b ,,types ,,of ,,climatic ,,sequence #a4 ,cosmic uniformity4 #g4 ,brueckner periods4 #b4 ,secular progression4 #h4 ,sunspot cycles4 #c4 ,geologic oscillations4 #i4 ,seasonal alternations4 #d4 ,glacial fluctuations4 #aj4 ,pleionian migrations4 #e4 ,orbital precessions4 #aa4 ,cyclonic vacillations4 #f4 ,historical pulsations4 #ab4 ,daily vibrations4 ---------------------------------------- ------------------- ,in assigning names to the various types an attempt has been made to indicate something of the nature of the sequence so far as duration1 periodicity1 and general tendencies are concerned4 ,not even the rich ,english language of the twentieth century1 however1 furnishes words with enough shades of meaning to express all that is desired4 ,moreover1 except in degree1 there is no sharp distinction between some of the related types1 such as glacial fluctuations and historic pulsations4 ,yet1 taken as a whole1 the table brings out the great contrast between two absolutely diverse extremes4 ,at the one end lies well-nigh eternal uniformity1 or an extremely slow progress in one direction throughout countless ages2 at the other1 rapid and regular vibrations from day to day1 or else irregular and seemingly unsystematic vacillations due to cyclonic storms1 both of which types are repeated millions of times during even a single glacial fluctuation4 ,the meaning of cosmic uniformity has been explained in the preceding chapter4 ,its relation to the other types of climatic sequences seems to be that it sets sharply defined limits beyond which no changes of any kind have ever gone since life1 as we know it1 first began4 ,secular progression1 on the other hand1 means that in spite of all manner of variations1 now this way and then the other1 the normal climate of the earth1 if there is such a thing1 has on the whole probably changed a little1 perhaps becoming more complex4 ,after each period of continental uplift and glaciation--for such are preeminently the times of complexity--it is doubtful whether the earth has ever returned to quite its former degree of monotony4 ,today the earth has swung away from the great diversity of the glacial period4 ,yet we still have contrasts of what seem to us great magnitude4 ,in low depressions1 such as ,turfan in the central deserts of ,eurasia1 the thermometer sometimes ranges from #j deg4,f4 in the morning to #fj deg4 in the shade at noon4 ,on a cloudy day in the ,amazon forest close to the seashore1 on the contrary1 the temperature for months may rise to #he deg4 by day and sink no lower than #ge deg4 at night4 ,the reasons for the secular progression of the earth's climate appear to be intimately connected with those which have caused the next1 and1 in many respects1 more important type of climatic sequence1 which consists of geological oscillations4 ,both the progression and the oscillations seem to depend largely on three purely terrestrial factors3 first1 the condition of the earth's interior1 including both internal heat and contraction2 second1 the salinity and movement of the ocean2 and third1 the composition and amount of the atmosphere4 ,to begin with the earth's interior--its loss of heat appears to be an almost negligible factor in explaining either secular progression or geologic oscillation4 ,according to both the nebular and the planetesimal hypotheses1 the earth's crust appears to be colder now than it was hundreds or thousands of millions of years ago4 ,the emission of internal heat1 however1 had probably ceased to be of much climatic significance near the beginning of the geological record1 for in southern ,canada glaciation occurred very early in the ,proterozoic era4 ,on the other hand1 the contraction of the earth has produced remarkable effects throughout the whole of geological time4 ,it has lessened the earth's circumference by a thousand miles or more1 as appears from the way in which the rocks have been folded and thrust bodily over one another4 ,according to the laws of dynamics this must have increased the speed of the earth's rotation1 thus shortening the day1 and also having the more important effect of increasing the bulge at the equator4 ,on the other hand1 recent investigations indicate that tidal retardation has probably diminished the earth's rate of rotation more than seemed probable a few years ago1 thus lengthening the day and diminishing the bulge at the equator4 ,thus two opposing forces have been at work1 one causing acceleration and one retardation4 ,their combined effect may have been a factor in causing secular progression of climate4 ,it almost certainly was of much importance in causing pronounced oscillations first one way and then the other4 ,this matter1 together with most of those touched in these first chapters1 will be expanded in later parts of the book4 ,on the whole the tendency appears to have been to create climatic diversity in place of uniformity4 ,the increasing salinity of the oceans may have been another factor in producing secular progression1 although of slight importance in respect to oscillations4 ,while the oceans were still growing in volume1 it is generally assumed that they must have been almost fresh for a vast period1 although ,chamberlin thinks that the change in salinity has been much less than is usually supposed4 ,so far as the early oceans were fresher than those of today1 their deep-sea circulation must have been less hampered than now by the heavy saline water which is produced by evaporation in warm regions4 ,although this saline water is warm1 its weight causes it to descend1 instead of moving poleward in a surface current2 this descent slows up the rise of the cold water which has moved along in the depths of the ocean from high latitudes1 and thus checks the general oceanic circulation4 ,if the ancient oceans were fresher and hence had a freer circulation than now1 a more rapid interchange of polar and equatorial water presumably tended to equalize the climate of all latitudes4 ,again1 although the earth's atmosphere has probably changed far less during geological times than was formerly supposed1 its composition has doubtless varied4 ,the total volume of nitrogen has probably increased1 for that gas is so inert that when it once becomes a part of the air it is almost sure to stay there4 ,on the other hand1 the proportions of oxygen1 carbon dioxide1 and water vapor must have fluctuated4 ,oxygen is taken out constantly by animals and by all the processes of rock weathering1 but on the other hand the supply is increased when plants break up new carbon dioxide derived from volcanoes4 ,as for the carbon dioxide1 it appears probable that in spite of the increased supply furnished by volcanoes the great amounts of carbon which have gradually been locked up in coal and limestone have appreciably depleted the atmosphere4 ,water vapor also may be less abundant now than in the past1 for the presence of carbon dioxide raises the temperature a little and thereby enables the air to hold more moisture4 ,when the area of the oceans has diminished1 and this has recurred very often1 this likewise would tend to reduce the water vapor4 ,moreover1 even a very slight diminution in the amount of heat given off by the earth1 or a decrease in evaporation because of higher salinity in the oceans1 would tend in the same direction4 ,now carbon dioxide and water vapor both have a strong blanketing effect whereby heat is prevented from leaving the earth4 ,therefore1 the probable reduction in the carbon dioxide and water vapor of the earth's atmosphere has apparently tended to reduce the climatic monotony and create diversity and complexity4 ,hence1 in spite of many reversals1 the general tendency of changes1 not only in the earth's interior and in the oceans1 but also in the atmosphere1 appears to be a secular progression from a relatively monotonous climate in which the evolution of higher organic forms would scarcely be rapid to an extremely diverse and complex climate highly favorable to progressive evolution4 ,the importance of these purely terrestrial agencies must not be lost sight of when we come to discuss other agencies outside the earth4 ,in ,table #b the next type of climatic sequence is geologic oscillation4 ,this means slow swings that last millions of years4 ,at one extreme of such an oscillation the climate all over the world is relatively monotonous2 it returns1 as it were1 toward the primeval conditions at the beginning of the secular progression4 ,at such times magnolias1 sequoias1 figs1 tree ferns1 and many other types of subtropical plants grew far north in places like ,greenland1 as is well known from their fossil remains of middle ,cenozoic time1 for example4 ,at these same times1 and also at many others before such high types of plants had evolved1 reef-making corals throve in great abundance in seas which covered what is now ,wisconsin1 ,michigan1 ,ontario1 and other equally cool regions4 ,today these regions have an average temperature of only about #gj deg4,f4 in the warmest month1 and average well below freezing in winter4 ,no reef-making corals can now live where the temperature averages below #fh deg4,f4 ,the resemblance of the ancient corals to those of today makes it highly probable that they were equally sensitive to low temperature4 ,thus1 in the mild portions of a geologic oscillation the climate seems to have been so equable and uniform that many plants and animals could live #aejj and at other times even #djjj miles farther from the equator than now4 ,at such times the lands in middle and high latitudes were low and small1 and the oceans extended widely over the continental platforms4 ,thus unhampered ocean currents had an opportunity to carry the heat of low latitudes far toward the poles4 ,under such conditions1 especially if the conception of the great subequatorial continent of ,gondwana land is correct1 the trade winds and the westerlies must have been stronger and steadier than now4 ,this would not only enable the westerlies1 which are really southwesterlies1 to carry more heat than now to high latitudes1 but would still further strengthen the ocean currents4 ,at the same time1 the air presumably contained an abundance of water vapor derived from the broad oceans1 and an abundance of atmospheric carbon dioxide inherited from a preceding time when volcanoes contributed much carbon dioxide to the air4 ,these two constituents of the atmosphere may have exercised a pronounced blanketing effect whereby the heat of the earth with its long wave lengths was kept in1 although the energy of the sun with its shorter wave lengths was not markedly kept out4 ,thus everything may have combined to produce mild conditions in high latitudes1 and to diminish the contrast between equator and pole1 and between summer and winter4 ,such conditions perhaps carry in themselves the seeds of decay4 ,at any rate while the lands lie quiet during a period of mild climate great strains must accumulate in the crust because of the earth's contraction and tidal retardation4 ,at the same time the great abundance of plants upon the lowlying plains with their mild climates1 and the marine creatures upon the broad continental platforms1 deplete the atmospheric carbon dioxide4 ,part of this is locked up as coal and part as limestone derived from marine plants as well as animals4 ,then something happens so that the strains and stresses of the crust are released4 ,the sea floors sink2 the continents become relatively high and large2 mountain ranges are formed2 and the former plains and emergent portions of the continental platforms are eroded into hills and valleys4 ,the large size of the continents tends to create deserts and other types of climatic diversity2 the presence of mountain ranges checks the free flow of winds and also creates diversity2 the ocean currents are likewise checked1 altered1 and diverted so that the flow of heat from low to high latitudes is diminished4 ,at the same time evaporation from the ocean diminishes so that a decrease in water vapor combines with the previous depletion of carbon dioxide to reduce the blanketing effect of the atmosphere4 ,thus upon periods of mild monotony there supervene periods of complexity1 diversity1 and severity4 ,turn to ,table #a and see how a glacial climate again and again succeeds a time when relative mildness prevailed almost everywhere4 ,or examine ,fig4 #a and notice how the lines representing temperatures go up and down4 ,in the figure ,schuchert makes it clear that when the lands have been large and mountain-making has been important1 as shown by the high parts of the lower shaded area1 the climate has been severe1 as shown by the descent of the snow line1 the upper shaded area4 ,in the diagram the climatic oscillations appear short1 but this is merely because they have been crowded together1 especially in the left hand or early part4 ,there an inch in length may represent a hundred million years4 ,even at the right-hand end an inch is equivalent to several million years4 ,the severe part of a climatic oscillation1 as well as the mild part1 will be shown in later chapters to bear in itself certain probable seeds of decay4 ,while the lands are being uplifted1 volcanic activity is likely to be vigorous and to add carbon dioxide to the air4 ,later1 as the mountains are worn down by the many agencies of water1 wind1 ice1 and chemical decay1 although much carbon dioxide is locked up by the carbonation of the rocks1 the carbon locked up in the coal is set free and increases the carbon dioxide of the air4 ,at the same time the continents settle slowly downward1 for the earth's crust though rigid as steel is nevertheless slightly viscous and will flow if subjected to sufficiently great and enduring pressure4 ,the area from which evaporation can take place is thereby increased because of the spread of the oceans over the continents1 and water vapor joins with the carbon dioxide to blanket the earth and thus tends to keep it uniformly warm4 ,moreover1 the diminution of the lands frees the ocean currents from restraint and permits them to flow more freely from low latitudes to high4 ,thus in the course of millions of years there is a return toward monotony4 ,ultimately1 however1 new stresses accumulate in the earth's crust1 and the way is prepared for another great oscillation4 ,perhaps the setting free of the stresses takes place simply because the strain at last becomes irresistible4 ,it is also possible1 as we shall see1 that an external agency sometimes adds to the strain and thereby determines the time at which a new oscillation shall begin4 ,in ,table #b the types of climatic sequences which follow geologic oscillations are glacial fluctuations1 orbital precessions and historical pulsations4 ,glacial fluctuations and historical pulsations appear to be of the same type1 except as to severity and duration1 and hence may be considered together4 ,they will be treated briefly here because the theories as to their causes are outlined in the next two chapters4 ,oddly enough1 although the historic pulsations lie much closer to us than do the glacial fluctuations1 they were not discovered until two or three generations later1 and are still much less known4 ,the most important feature of both sequences is the swing from a glacial to an inter-glacial epoch or from the arsis or accentuated part of an historical pulsation to the thesis or unaccented part4 ,in a glacial epoch or in the arsis of an historic pulsation1 storms are usually abundant and severe1 the mean temperature is lower than usual1 snow accumulates in high latitudes or upon lofty mountains4 ,for example1 in the last such period during the fourteenth century1 great floods and droughts occurred alternately around the ,north ,sea2 it was several times possible to cross the ,baltic ,sea from ,germany to ,sweden on the ice1 and the ice of ,greenland advanced so much that shore ice caused the ,norsemen to change their sailing route between ,iceland and the ,norse colonies in southern ,greenland4 ,at the same time in low latitudes and in parts of the continental interior there is a tendency toward diminished rainfall and even toward aridity and the formation of deserts4 ,in ,yucatan1 for example1 a diminution in tropical rainfall in the fourteenth century seems to have given the ,mayas a last opportunity for a revival of their decaying civilization4 ,illustration3 ,fig4 #a4 ,climatic changes and mountain building4 7,after ,schuchert1 in ,the ,evolution of the ,earth and ,its ,inhabitants1 edited by ,r4 ,s4 ,lull47 ,diagram showing the times and probable extent of the more or less marked climate changes in the geologic history of ,north ,america1 and of its elevation into chains of mountains4 ,among the climatic sequences1 glacial fluctuations are perhaps of the most vital import from the standpoint of organic evolution2 from the standpoint of human history the same is true of climatic pulsations4 ,glacial epochs have repeatedly wiped out thousands upon thousands of species and played a part in the origin of entirely new types of plants and animals4 ,this is best seen when the life of the ,pennsylvanian is contrasted with that of the ,permian4 ,an historic pulsation may wipe out an entire civilization and permit a new one to grow up with a radically different character4 ,hence it is not strange that the causes of such climatic phenomena have been discussed with extraordinary vigor4 ,in few realms of science has there been a more imposing or more interesting array of theories4 ,in this book we shall consider the more important of these theories4 ,a new solar or cyclonic hypothesis and the hypothesis of changes in the form and altitude of the land will receive the most attention1 but the other chief hypotheses are outlined in the next chapter1 and are frequently referred to throughout the volume4 ,between glacial fluctuations and historical pulsations in duration1 but probably less severe than either1 come orbital precessions4 ,these stand in a group by themselves and are more akin to seasonal alternations than to any other type of climatic sequence4 ,they must have occurred with absolute regularity ever since the earth began to revolve around the sun in its present elliptical orbit4 ,since the orbit is elliptical and since the sun is in one of the two foci of the ellipse1 the earth's distance from the sun varies4 ,at present the earth is nearest the sun in the northern winter4 ,hence the rigor of winter in the northern hemisphere is mitigated1 while that of the southern hemisphere is increased4 ,in about ten thousand years this condition will be reversed1 and in another ten thousand the present conditions will return once more4 ,such climatic precessions1 as we may here call them1 must have occurred unnumbered times in the past1 but they do not appear to have been large enough to leave in the fossils of the rocks any traces that can be distinguished from those of other climatic sequences4 ,we come now to ,brueckner periods and sunspot cycles4 ,the ,brueckner periods have a length of about thirty-three years4 ,their existence was suggested at least as long ago as the days of ,sir ,francis ,bacon1 whose statement about them is quoted on the flyleaf of this book4 ,they have since been detected by a careful study of the records of the time of harvest1 vintage1 the opening of rivers to navigation1 and the rise or fall of lakes like the ,caspian ,sea4 ,in his book on ,klimaschwankungen seit #agjj1 ,brueckner has collected an uncommonly interesting assortment of facts as to the climate of ,europe for more than two centuries4 ,more recently1 by a study of the rate of growth of trees1 ,douglass1 in his book on ,climatic ,cycles and ,tree ,growth1 has carried the subject still further4 ,in general the nature of the #cc-year periods seems to be identical with that of the #aa- or #ab- year sunspot cycle1 on the one hand1 and of historic pulsations on the other4 ,for a century observers have noted that the variations in the weather which everyone notices from year to year seem to have some relation to sunspots4 ,for generations1 however1 the relationship was discussed without leading to any definite conclusion4 ,the trouble was that the same change was supposed to take place in all parts of the world4 ,hence1 when every sort of change was found somewhere at any given sunspot stage1 it seemed as though there could not be a relationship4 ,of late years1 however1 the matter has become fairly clear4 ,the chief conclusions are1 first1 that when sunspots are numerous the average temperature of the earth's surface is lower than normal4 ,this does not mean that all parts are cooler1 for while certain large areas grow cool1 others of less extent become warm at times of many sunspots4 ,second1 at times of many sunspots storms are more abundant than usual1 but are also confined somewhat closely to certain limited tracks so that elsewhere a diminution of storminess may be noted4 ,this whole question is discussed so fully in ,earth and ,sun that it need not detain us further in this preliminary view of the whole problem of climate4 ,suffice it to say that a study of the sunspot cycle leads to the conclusion that it furnishes a clue to many of the unsolved problems of the climate of the past1 as well as a key to prediction of the future4 ,passing by the seasonal alternations which are fully explained as the result of the revolution of the earth around the sun1 we may merely point out that1 like the daily vibrations which bring ,table #b to a close1 they emphasize the outstanding fact that the main control of terrestrial climate is the amount of energy received from the sun4 ,this same principle is illustrated by pleionian migrations4 ,the term pleion comes from a ,greek word meaning more4 ,it was taken by ,arctowski to designate areas or periods where there is an excess of some climatic element1 such as atmospheric pressure1 rainfall1 or temperature4 ,even if the effect of the seasons is eliminated1 it appears that the course of these various elements does not run smoothly4 ,as everyone knows1 a period like the autumn of #aibj in the eastern ,united ,states may be unusually warm1 while a succeeding period may be unseasonably cool4 ,these departures from the normal show a certain rough periodicity4 ,for example1 there is evidence of a period of about twenty-seven days1 corresponding to the sun's rotation and formerly supposed to be due to the moon's revolution which occupies almost the same length of time4 ,still other periods appear to have an average duration of about three months and of between two and three years4 ,two remarkable discoveries have recently been made in respect to such pleions4 ,one is that a given type of change usually occurs simultaneously in a number of well-defined but widely separated centers1 while a change of an opposite character arises in another equally well-defined1 but quite different1 set of centers4 ,in general1 areas of high pressure have one type of change and areas of low pressure the other type4 ,so systematic are these relationships and so completely do they harmonize in widely separated parts of the earth1 that it seems certain that they must be due to some outside cause1 which in all probability can be only the sun4 ,the second discovery is that pleions1 when once formed1 travel irregularly along the earth's surface4 ,their paths have not yet been worked out in detail1 but a general migration seems well established4 ,because of this1 it is probable that if unusually warm weather prevails in one part of a continent at a given time1 the thermo-pleion1 or excess of heat1 will not vanish but will gradually move away in some particular direction4 ,if we knew the path that it would follow we might predict the general temperature along its course for some months in advance4 ,the paths are often irregular1 and the pleions frequently show a tendency to break up or suddenly revive4 ,probably this tendency is due to variations in the sun4 ,when the sun is highly variable1 the pleions are numerous and strong1 and extremes of weather are frequent4 ,taken as a whole the pleions offer one of the most interesting and hopeful fields not only for the student of the causes of climatic variations1 but for the man who is interested in the practical question of long-range weather forecasts4 ,like many other climatic phenomena they seem to represent the combined effect of conditions in the sun and upon the earth itself4 ,the last of the climatic sequences which require explanation is the cyclonic vacillations4 ,these are familiar to everyone1 for they are the changes of weather which occur at intervals of a few days1 or a week or two1 at all seasons1 in large parts of the ,united ,states1 ,europe1 ,japan1 and some of the other progressive parts of the earth4 ,they do not1 however1 occur with great frequency in equatorial regions1 deserts1 and many other regions4 ,up to the end of the last century1 it was generally supposed that cyclonic storms were purely terrestrial in origin4 ,without any adequate investigation it was assumed that all irregularities in the planetary circulation of the winds arise from an irregular distribution of heat due to conditions within or upon the earth itself4 ,these irregularities were supposed to produce cyclonic storms in certain limited belts1 but not in most parts of the world4 ,today this view is being rapidly modified4 ,undoubtedly1 the irregularities due to purely terrestrial conditions are one of the chief contributory causes of storms1 but it begins to appear that solar variations also play a part4 ,it has been found1 for example1 that not only the mean temperature of the earth's surface varies in harmony with the sunspot cycle1 but that the frequency and severity of storms vary in the same way4 ,moreover1 it has been demonstrated that the sun's radiation is not constant1 but is subject to innumerable variations4 ,this does not mean that the sun's general temperature varies1 but merely that at some times heated gases are ejected rapidly to high levels so that a sudden wave of energy strikes the earth4 ,thus1 the present tendency is to believe that the cyclonic variations1 the changes of weather which come and go in such a haphazard1 irresponsible way1 are partly due to causes pertaining to the earth itself and partly to the sun4 ,from this rapid survey of the types of climatic sequences1 it is evident that they may be divided into four great groups4 ,first comes cosmic uniformity1 one of the most marvelous and incomprehensible of all known facts4 ,we simply have no explanation which is in any respect adequate4 ,next come secular progression and geologic oscillations1 two types of change which seem to be due mainly to purely terrestrial causes1 that is1 to changes in the lands1 the oceans1 and the air4 ,the general tendency of these changes is toward complexity and diversity1 thus producing progression1 but they are subject to frequent reversals which give rise to oscillations lasting millions of years4 ,the processes by which the oscillations take place are fully discussed in this book4 ,nevertheless1 because they are fairly well understood1 they are deferred until after the third group of sequences has been discussed4 ,this group includes glacial fluctuations1 historic pulsations1 ,brueckner periods1 sunspot cycles1 pleionian migrations1 and cyclonic vacillations4 ,the outstanding fact in regard to all of these is that while they are greatly modified by purely terrestrial conditions1 they seem to owe their origin to variations in the sun4 ,they form the chief subject of ,earth and ,sun and in their larger phases are the most important topic of this book also4 ,the last group of sequences includes orbital precessions1 seasonal alternations1 and daily variations4 ,these may be regarded as purely solar in origin4 ,yet their influence1 like that of each of the other groups1 is much modified by the earth's own conditions4 ,our main problem is to separate and explain the two great elements in climatic changes1--the effects of the sun1 on the one hand1 and of the earth on the other4 ,,chapter ,,iii ,,hypotheses ,,of ,,climatic ,,change ,the next step in our study of climate is to review the main hypotheses as to the causes of glaciation4 ,these hypotheses apply also to other types of climatic changes4 ,we shall concentrate on glacial periods1 however1 not only because they are the most dramatic and well-known types of change1 but because they have been more discussed than any other and have also had great influence on evolution4 ,moreover1 they stand near the middle of the types of climatic sequences1 and an understanding of them does much to explain the others4 ,in reviewing the various theories we shall not attempt to cover all the ground1 but shall merely state the main ideas of the few theories which have had an important influence upon scientific thought4 ,the conditions which any satisfactory climatic hypothesis must satisfy are briefly as follows3 7#a7 ,due weight must be given to the fact that changes of climate are almost certainly due to the combined effect of a variety of causes1 both terrestrial and solar or cosmic4 7#b7 ,attention must also be paid to both sides in the long controversy as to whether glaciation is due primarily to a diminution in the earth's supply of heat or to a redistribution of the heat through changes in atmospheric and oceanic circulation4 ,at present the great majority of authorities are on the side of a diminution of heat1 but the other view also deserves study4 7#c7 ,a satisfactory hypothesis must explain the frequent synchronism between two great types of phenomena2 first1 movements of the earth's crust whereby continents are uplifted and mountains upheaved2 and1 second1 great changes of climate which are usually marked by relatively rapid oscillations from one extreme to another4 7#d7 ,no hypothesis can find acceptance unless it satisfies the somewhat exacting requirements of the geological record1 with its frequent but irregular repetition of long1 mild periods1 relatively cool or intermediate periods like the present1 and glacial periods of more or less severity and perhaps accompanying the more or less widespread uplifting of continents4 ,at least during the later glacial periods the hypothesis must explain numerous climatic epochs and stages superposed upon a single general period of continental upheaval4 ,moreover1 although historical geology demands cycles of varied duration and magnitude1 it does not furnish evidence of any rigid periodicity causing the cycles to be uniform in length or intensity4 7#e7 ,most important of all1 a satisfactory explanation of climatic changes and crustal deformation must take account of all the agencies which are now causing similar phenomena4 ,whether any other agencies should be considered is open to question1 although the relative importance of existing agencies may have varied4 ,i4 ,croll's ,eccentricity ,theory4 ,one of the most ingenious and most carefully elaborated scientific hypotheses is ,croll's#aj precessional hypothesis as to the effect of the earth's own motions4 ,so well was this worked out that it was widely accepted for a time and still finds a place in popular but unscientific books1 such as ,wells' ,outline of ,history1 and even in scientific works like ,wright's ,quaternary ,ice ,age4 ,the gist of the hypothesis has already been given in connection with the type of climatic sequence known as orbital precessions4 ,the earth is #ic million miles away from the sun in ,january and #ig million in ,july4 ,the earth's axis precesses1 however1 just as does that of a spinning top4 ,hence arises what is known as the precession of the equinoxes1 that is1 a steady change in the season at which the earth is in perihelion1 or nearest to the sun4 ,in the course of #ba1jjj years the time of perihelion varies from early in ,january through the entire twelve months and back to ,january4 ,moreover1 the earth's orbit is slightly more elliptical at certain periods than at others1 for the planets sometimes become bunched so that they all pull the earth in one direction4 ,hence1 once in about one hundred thousand years the effect of the elliptical shape of the earth's orbit is at a maximum4 ,croll argued that these astronomical changes must alter the earth's climate1 especially by their effect on winds and ocean currents4 ,his elaborate argument contains a vast amount of valuable material4 ,later investigation1 however1 seems to have proven the inadequacy of his hypothesis4 ,in the first place1 the supposed cause does not seem nearly sufficient to produce the observed results4 ,second1 ,croll's hypothesis demands that glaciation in the northern and southern hemisphere take place alternately4 ,a constantly growing collection of facts1 however1 indicates that glaciation does not occur in the two hemispheres alternately1 but at the same time4 ,third1 the hypothesis calls for the constant and frequent repetition of glaciation at absolutely regular intervals4 ,the geological record shows no such regularity1 for sometimes several glacial epochs follow in relatively close succession at irregular intervals of perhaps fifty to two hundred thousand years1 and thus form a glacial period2 and then for millions of years there are none4 ,fourth1 the eccentricity hypothesis provides no adequate explanation for the glacial stages or subepochs1 the historic pulsations1 and the other smaller climatic variations which are superposed upon glacial epochs and upon one another in bewildering confusion4 ,in spite of these objections1 there can be little question that the eccentricity of the earth's orbit and the precession of the equinoxes with the resulting change in the season of perihelion must have some climatic effect4 ,hence ,croll's theory deserves a permanent though minor place in any full discussion of the causes of climatic changes4 ,,ii4 ,the ,carbon ,dioxide ,theory4 ,at about the time that the eccentricity theory was being relegated to a minor niche1 a new theory was being developed which soon exerted a profound influence upon geological thought4 ,chamberlin1#aa adopting an idea suggested by ,tyndall1 fired the imagination of geologists by his skillful exposition of the part played by carbon dioxide in causing climatic changes4 ,today this theory is probably more widely accepted than any other4 ,we have already seen that the amount of carbon dioxide gas in the atmosphere has a decided climatic importance4 ,moreover1 there can be little doubt that the amount of that gas in the atmosphere varies from age to age in response to the extent to which it is set free by volcanoes1 consumed by plants1 combined with rocks in the process of weathering1 dissolved in the ocean or locked up in the form of coal and limestone4 ,the main question is whether such variations can produce changes so rapid as glacial epochs and historical pulsations4 ,abundant evidence seems to show that the degree to which the air can be warmed by carbon dioxide is sharply limited4 ,humphreys1 in his excellent book on the ,physics of the ,air1 calculates that a layer of carbon dioxide forty centimeters thick has practically as much blanketing effect as a layer indefinitely thicker4 ,in other words1 forty centimeters of carbon dioxide1 while having no appreciable effect on sunlight coming toward the earth1 would filter out and thus retain in the atmosphere all the outgoing terrestrial heat that carbon dioxide is capable of absorbing4 ,adding more would be like adding another filter when the one in operation has already done all that that particular kind of filter is capable of doing4 ,according to ,humphreys' calculations1 a doubling of the carbon dioxide in the air would in itself raise the average temperature about #a4c deg4,c4 and further carbon dioxide would have practically no effect4 ,reducing the present supply by half would reduce the temperature by essentially the same amount4 ,the effect must be greater1 however1 than would appear from the figures given above1 for any change in temperature has an effect on the amount of water vapor1 which in turn causes further changes of temperature4 ,moreover1 as ,chamberlin points out1 it is not clear whether ,humphreys allows for the fact that when the #dj centimeters of ,,co#b nearest the earth has been heated by terrestrial radiation1 it in turn radiates half its heat outward and half inward4 ,the outward half is all absorbed in the next layer of carbon dioxide1 and so on4 ,the process is much more complex than this1 but the end result is that even the last increment of ,,co#b1 that is1 the outermost portions in the upper atmosphere1 must apparently absorb an infinitesimally small amount of heat4 ,this fact1 plus the effect of water vapor1 would seem to indicate that a doubling or halving of the amount of ,,co#b1 would have an effect of more than #a4c deg4,c4 ,a change of even #b deg4,c4 above or below the present level of the earth's mean temperature would be of very appreciable climatic significance1 for it is commonly believed that during the height of the glacial period the mean temperature was only #e deg4 to #h deg4,c4 lower than now4 ,nevertheless1 variations in atmospheric carbon dioxide do not necessarily seem competent to produce the relatively rapid climatic fluctuations of glacial epochs and historic pulsations as distinguished from the longer swings of glacial periods and geological eras4 ,in ,chamberlin's view1 as in ours1 the elevation of the land1 the modification of the currents of the air and of the ocean1 and all that goes with elevation as a topographic agency constitute a primary cause of climatic changes4 ,a special effect of this is the removal of carbon dioxide from the air by the enhanced processes of weathering4 ,this1 as he carefully states1 is a very slow process1 and cannot of itself lead to anything so sudden as the oncoming of glaciation4 ,but here comes ,chamberlin's most distinctive contribution to the subject1 namely1 the hypothesis that changes in atmospheric temperature arising from variations in atmospheric carbon dioxide are able to cause a reversal of the deep-sea oceanic circulation4 ,according to ,chamberlin's view1 the ordinary oceanic circulation of the greater part of geological time was the reverse of the present circulation4 ,warm water descended to the ocean depths in low latitudes1 kept its heat while creeping slowly poleward1 and rose in high latitudes producing the warm climate which enabled corals1 for example1 to grow in high latitudes4 ,chamberlin holds this opinion largely because there seems to him to be no other reasonable way to account for the enormously long warm periods when heat-loving forms of life lived in what are now polar regions of ice and snow4 ,he explains this reversed circulation by supposing that an abundance of atmospheric carbon dioxide1 together with a broad distribution of the oceans1 made the atmosphere so warm that the evaporation in low latitudes was far more rapid than now4 ,hence the surface water of the ocean became a relatively concentrated brine4 ,such a brine is heavy and tends to sink1 thereby setting up an oceanic circulation the reverse of that which now prevails4 ,at present the polar waters sink because they are cold and hence contract4 ,moreover1 when they freeze a certain amount of salt leaves the ice and thereby increases the salinity of the surrounding water4 ,thus the polar water sinks to the depths of the ocean1 its place is taken by warmer and lighter water from low latitudes which moves poleward along the surface1 and at the same time the cold water of the ocean depths is forced equatorward below the surface4 ,but if the equatorial waters were so concentrated that a steady supply of highly saline water kept descending to low levels1 the direction of the circulation would have to be reversed4 ,the time when this would occur would depend upon the delicate balance between the downward tendencies of the cold polar water and of the warm saline equatorial water4 ,suppose that while such a reversed circulation prevailed1 the atmospheric ,,co#b should be depleted1 and the air cooled so much that the concentration of the equatorial waters by evaporation was no longer sufficient to cause them to sink4 ,a reversal would take place1 the present type of circulation would be inaugurated1 and the whole earth would suffer a chill because the surface of the ocean would become cool4 ,the cool surface-water would absorb carbon dioxide faster than the previous warm water had done1 for heat drives off gases from water4 ,this would hasten the cooling of the atmosphere still more1 not only directly but by diminishing the supply of atmospheric moisture4 ,the result would be glaciation4 ,but ultimately the cold waters of the higher latitudes would absorb all the carbon dioxide they could hold1 the slow equatorward creep would at length permit the cold water to rise to the surface in low latitudes4 ,there the warmth of the equatorial sun and the depleted supply of carbon dioxide in the air would combine to cause the water to give up its carbon dioxide once more4 ,if the atmosphere had been sufficiently depleted by that time1 the rising waters in low latitudes might give up more carbon dioxide than the cold polar waters absorbed4 ,thus the atmospheric supply would increase1 the air would again grow warm1 and a tendency toward deglaciation1 or toward an inter-glacial condition would arise4 ,at such times the oceanic circulation is not supposed to have been reversed1 but merely to have been checked and made slower by the increasing warmth4 ,thus inter-glacial conditions like those of today1 or even considerably warmer1 are supposed to have been produced with the present type of circulation4 ,the emission of carbon dioxide in low latitudes could not permanently exceed the absorption in high latitudes4 ,after the present type of circulation was finally established1 which might take tens of thousands of years1 the two would gradually become equal4 ,then the conditions which originally caused the oceanic circulation to be reversed would again destroy the balance2 the atmospheric carbon dioxide would be depleted2 the air would grow cooler2 and the cycle of glaciation would be repeated4 ,each cycle would be shorter than the last1 for not only would the swings diminish like those of a pendulum1 but the agencies that were causing the main depletion of the atmospheric carbon dioxide would diminish in intensity4 ,finally as the lands became lower through erosion and submergence1 and as the processes of weathering became correspondingly slow1 the air would gradually be able to accumulate carbon dioxide2 the temperature would increase2 and at length the oceanic circulation would be reversed again4 ,when the warm saline waters of low latitudes finally began to sink and to set up a flow of warm water poleward in the depths of the ocean1 a glacial period would definitely come to an end4 ,this hypothesis has been so skillfully elaborated1 and contains so many important elements that one can scarcely study it without profound admiration4 ,we believe that it is of the utmost value as a step toward the truth1 and especially because it emphasizes the great function of oceanic circulation4 ,nevertheless1 we are unable to accept it in full for several reasons1 which may here be stated very briefly4 ,most of them will be discussed fully in later pages4 7#a7 ,while a reversal of the deep-sea circulation would undoubtedly be of great climatic importance and would produce a warm climate in high latitudes1 we see no direct evidence of such a reversal4 ,it is equally true that there is no conclusive evidence against it1 and the possibility of a reversal must not be overlooked4 ,there seem1 however1 to be other modifications of atmospheric and oceanic circulation which are able to produce the observed results4 7#b7 ,there is much1 and we believe conclusive1 evidence that a mere lowering of temperature would not produce glaciation4 ,what seems to be needed is changes in atmospheric circulation and in precipitation4 ,the carbon dioxide hypothesis has not been nearly so fully developed on the meteorological side as in other respects4 7#c7 ,the carbon dioxide hypothesis seems to demand that the oceans should have been almost as saline as now in the ,proterozoic era at the time of the first known glaciation4 ,chamberlin holds that such was the case1 but the constant supply of saline material brought to the ocean by rivers and the relatively small deposition of such material on the sea floor seem to indicate that the early oceans must have been much fresher than those of today4 7#d7 ,the carbon dioxide hypothesis does not attempt to explain minor climatic fluctuations such as post-glacial stages and historic pulsations1 but these appear to be of the same nature as glacial epochs1 differing only in degree4 7#e7 ,another reason for hesitation in accepting the carbon dioxide hypothesis as a full explanation of glacial fluctuations is the highly complex and non-observational character of the explanation of the alternation of glacial and inter-glacial epochs and of their constantly decreasing length4 7#f7 ,most important of all1 a study of the variations of weather and of climate as they are disclosed by present records and by the historic past suggests that there are now in action certain other causes which are competent to explain glaciation without recourse to a process whose action is beyond the realm of observation4 ,these considerations lead to the conclusion that the carbon dioxide hypothesis and the reversal of the oceanic circulation should be regarded as a tentative rather than a final explanation of glaciation4 ,nevertheless1 the action of carbon dioxide seems to be an important factor in producing the longer oscillations of climate from one geological era to another4 ,it probably plays a considerable part in preparing the way for glacial periods and in making it possible for other factors to produce the more rapid changes which have so deeply influenced organic evolution4 ,,iii4 ,the ,form of the ,land4 ,another great cause of climatic change consists of a group of connected phenomena dependent upon movements of the earth's crust4 ,as to the climatic potency of changes in the lands there is practical agreement among students of climatology and glaciation4 ,that the height and extent of the continents1 the location1 size1 and orientation of mountain ranges1 and the opening and closing of oceanic gateways at places like ,panama1 and the consequent diversion of oceanic currents1 exert a profound effect upon climate can scarcely be questioned4 ,such changes may be introduced rapidly1 but their disappearance is usually slow compared with the rapid pulsations to which climate has been subject during historic times and during stages of glacial retreat and advance1 or even in comparison with the epochs into which the ,pleistocene1 ,permian1 and perhaps earlier glacial periods have been divided4 ,hence1 while crustal movements appear to be more important than the eccentricity of the earth's orbit or the amount of carbon dioxide in the air1 they do not satisfactorily explain glacial fluctuations1 historic pulsations1 and especially the present little cycles of climatic change4 ,all these changes involve a relatively rapid swing from one extreme to another1 while an upheaval of a continent1 which is at best a slow geologic process1 apparently cannot be undone for a long1 long time4 ,hence such an upheaval1 if acting alone1 would lead to a relatively long-lived climate of a somewhat extreme type4 ,it would help to explain the long swings1 or geologic oscillations between a mild and uniform climate at one extreme1 and a complex and varied climate at the other1 but it would not explain the rapid climatic pulsations which are closely associated with great movements of the earth's crust4 ,it might prepare the way for them1 but could not cause them4 ,that this conclusion is true is borne out by the fact that vast mountain ranges1 like those at the close of the ,jurassic and ,cretaceous1 are upheaved without bringing on glacial climates4 ,moreover1 the marked ,permian ice age follows long after the birth of the ,hercynian ,mountains and before the rise of others of later ,permian origin4 ,,iv4 ,the ,volcanic ,hypothesis4 ,in the search for some cause of climatic change which is highly efficient and yet able to vary rapidly and independently1 ,abbot1 ,fowle1 ,humphreys1 and others1#ab have concluded that volcanic eruptions are the missing agency4 ,in ,physics of the ,air1 ,humphreys gives a careful study of the effect of volcanic dust upon terrestrial temperature4 ,he begins with a mathematical investigation of the size of dust particles1 and their quantity after certain eruptions4 ,he demonstrates that the power of such particles to deflect light of short wave-lengths coming from the sun is perhaps thirty times more than their power to retain the heat radiated in long waves from the earth4 ,hence it is estimated that if a ,krakatoa were to belch forth dust every year or two1 the dust veil might cause a reduction of about #f deg4,c4 in the earth's surface temperature4 ,as in every such complicated problem1 some of the author's assumptions are open to question1 but this touches their quantitative and not their qualitative value4 ,it seems certain that if volcanic explosions were frequent enough and violent enough1 the temperature of the earth's surface would be considerably lowered4 ,actual observation supports this theoretical conclusion4 ,humphreys gathers together and amplifies all that he and ,abbot and ,fowle have previously said as to observations of the sun's thermal radiation by means of the pyrheliometer4 ,this summing up of the relations between the heat received from the sun1 and the occurrence of explosive volcanic eruptions leaves little room for doubt that at frequent intervals during the last century and a half a slight lowering of terrestrial temperature has actually occurred after great eruptions4 ,nevertheless1 it does not justify ,humphreys' final conclusion that phenomena within the earth itself suffice to modify its own climate1 444 that these and these alone have actually caused great changes time and again in the geologic past4 ,humphreys sees so clearly the importance of the purely terrestrial point of view that he unconsciously slights the cosmic standpoint and ignores the important solar facts which he himself adduces elsewhere at considerable length4 ,in addition to this the degree to which the temperature of the earth as a whole is influenced by volcanic eruptions is by no means so clear as is the fact that there is some influence4 ,arctowski1#ac for example1 has prepared numerous curves showing the march of temperature month after month for many years4 ,during the period from #aiji to #aiac1 which includes the great eruption of ,katmai in ,alaska1 low temperature is found to have prevailed at the time of the eruption1 but1 as ,arctowski puts it1 on the basis of the curves for #aej stations in all parts of the world3 ,the supposition that these abnormally low temperatures were due to the veil of volcanic dust produced by the ,katmai eruption of ,june #f1 #aiab1 is completely out of the question4 ,if that had been the case1 temperature would have decreased from that date on1 whereas it was decreasing for more than a year before that date4 ,koeppen1#ad in his comprehensive study of temperature for a hundred years1 also presents a strong argument against the idea that volcanic eruptions have an important place in determining the present temperature of the earth4 ,a volcanic eruption is a sudden occurrence4 ,whatever effect is produced by dust thrown into the air must occur within a few months1 or as soon as the dust has had an opportunity to be wafted to the region in question4 ,when the dust arrives1 there will be a rapid drop through the few degrees of temperature which the dust is supposed to be able to account for1 and thereafter a slow rise of temperature4 ,if volcanic eruptions actually caused a frequent lowering of terrestrial temperature in the hundred years studied by ,koeppen1 there should be more cases where the annual temperature is decidedly below the normal than where it shows a large departure in the opposite direction4 ,the contrary is actually the case4 ,a still more important argument is the fact that the earth is now in an intermediate condition of climate4 ,throughout most of geologic time1 as we shall see again and again1 the climate of the earth has been milder than now4 ,regions like ,greenland have not been the seat of glaciers1 but have been the home of types of plants which now thrive in relatively low latitudes4 ,in other words1 the earth is today only part way from a glacial epoch to what may be called the normal1 mild climate of the earth--a climate in which the contrast from zone to zone was much less than now1 and the lower air averaged warmer4 ,hence it seems impossible to avoid the conclusion that the cause of glaciation is still operating with considerable although diminished efficiency4 ,but volcanic dust is obviously not operating to any appreciable extent at present1 for the upper air is almost free from dust a large part of the time4 ,again1 as ,chamberlin suggests1 let it be supposed that a ,krakatoan eruption every two years would produce a glacial period4 ,unless the most experienced field workers on the glacial formations are quite in error1 the various glacial epochs of the ,pleistocene glacial period had a joint duration of at least #aej1jjj years and perhaps twice as much4 ,that would require #ge1jjj ,krakatoan eruptions4 ,but where are the pits and cones of such eruptions8 ,there has not been time to erode them away since the ,pleistocene glaciation4 ,their beds of volcanic ash would presumably be as voluminous as the glacial beds1 but there do not seem to be accumulations of any such size4 ,even though the same volcano suffered repeated explosions1 it seems impossible to find sufficient fresh volcanic debris4 ,moreover1 the volcanic hypothesis has not yet offered any mechanism for systematic glacial variations4 ,hence1 while the hypothesis is important1 we must search further for the full explanation of glacial fluctuations1 historic pulsations1 and the earth's present quasi-glacial climate4 ,v4 ,the ,hypothesis of ,polar ,wandering4 ,another hypothesis1 which has some adherents1 especially among geologists1 holds that the position of the earth's axis has shifted repeatedly during geological times1 thus causing glaciation in regions which are not now polar4 ,astrophysicists1 however1 are quite sure that no agency could radically change the relation between the earth and its axis without likewise altering the orbits of the planets to a degree that would be easily recognized4 ,moreover1 the distribution of the centers of glaciation both in the ,permian and ,pleistocene periods does not seem to conform to this hypothesis4 ,,vi4 ,the ,thermal ,solar ,hypothesis4 ,the only other explanations of the climatic changes of glacial and historic times which now seem to have much standing are two distinct and almost antagonistic solar hypotheses4 ,one is the idea that changes in the earth's climate are due to variations in the heat emitted by the sun and hence in the temperature of the earth4 ,the other is the entirely different idea that climatic changes arise from solar conditions which cause a redistribution of the earth's atmospheric pressure and hence produce changes in winds1 ocean currents1 and especially storms4 ,this second1 or cyclonic1 hypothesis is the subject of a book entitled ,earth and ,sun1 which is to be published as a companion to the present volume4 ,it will be outlined in the next chapter4 ,the other1 or thermal1 hypothesis may be dismissed briefly4 ,unquestionably a permanent change in the amount of heat emitted by the sun would permanently alter the earth's climate4 ,there is absolutely no evidence1 however1 of any such change during geologic time4 ,the evidence as to the earth's cosmic uniformity and as to secular progression is all against it4 ,suppose that for thirty or forty thousand years the sun cooled off enough so that the earth was as cool as during a glacial epoch4 ,as glaciation is soon succeeded by a mild climate1 some agency would then be needed to raise the sun's temperature4 ,the impact of a shower of meteorites might accomplish this1 but that would mean a very sudden heating1 such as there is no evidence of in geological history4 ,in fact1 there is far more evidence of sudden cooling than of sudden heating4 ,moreover1 it is far beyond the bounds of probability that such an impact should be repeated again and again with just such force as to bring the climate back almost to where it started and yet to allow for the slight changes which cause secular progression4 ,another and equally cogent objection to the thermal form of solar hypothesis is stated by ,humphreys as follows3 ,a change of the solar constant obviously alters all surface temperatures by a roughly constant percentage4 ,hence a decrease of the heat from the sun would in general cause a decrease of the interzonal temperature gradients2 and this in turn a less vigorous atmospheric circulation1 and a less copious rain or snowfall--exactly the reverse of the condition1 namely1 abundant precipitation1 most favorable to extensive glaciation4 ,this brings us to the end of the main hypotheses as to climatic changes1 aside from the solar cyclonic hypothesis which will be discussed in the next chapter4 ,it appears that variations in the position of the earth at perihelion have a real though slight influence in causing cycles with a length of about #ba1jjj years4 ,changes in the carbon dioxide of the air probably have a more important but extremely slow influence upon geologic oscillations4 ,variations in the size1 shape1 and height of the continents are constantly causing all manner of climatic complications1 but do not cause rapid fluctuations and pulsations4 ,the eruption of volcanic dust appears occasionally to lower the temperature1 but its potency to explain the complex climatic changes recorded in the rocks has probably been exaggerated4 ,finally1 although minor changes in the amount of heat given out by the sun occur constantly and have been demonstrated to have a climatic effect1 there is no evidence that such changes are the main cause of the climatic phenomena which we are trying to explain4 ,nevertheless1 in connection with other solar changes they may be of high importance4 ,,footnotes3 ,footnote #aj3 ,james ,croll3 ,climate and ,time1 #ahgf4 ,footnote #aa3 ,t4 ,c4 ,chamberlin3 ,an attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis2 ,jour4 ,geol41 ,vol4 ,,vii1 #ahii1 pp4 #ede-ehd1 #ffg-fhe1 #geg-ghg4 ,t4 ,c4 ,chamberlin and ,r4 ,d4 ,salisbury3 ,geology1 ,vol4 ,,ii1 #aijf1 pp4 #ic-ajf1 #fee-fgg1 and ,vol4 ,,iii1 pp4 #dcb-ddf4 ,s4 ,arrhenius 7,kosmische ,physik1 ,vol4 ,,ii1 #aijc1 p4 #ejc7 carried out some investigations on carbon dioxide which have had a pronounced effect on later conclusions4 ,f4 ,frech adopted ,arrhenius' idea and developed it in a paper entitled ,ueber die ,klima-,aenderungen der ,geologischen ,vergangenheit4 ,compte ,rendu1 ,tenth 7,mexico7 ,congr4 ,geol4 ,intern41 #aijg 7#aijh71 pp4 #bii-cbe4 ,the exact origin of the carbon dioxide theory has been stated so variously that it seems worth while to give the exact facts4 ,prompted by the suggestion1 of ,tyndall that glaciation might be due to depletion of atmospheric carbon dioxide1 ,chamberlin worked up the essentials of his early views before he saw any publication from ,arrhenius1 to whom the idea has often been attributed4 ,in #ahie or earlier ,chamberlin began to give the carbon dioxide hypothesis to his students and to discuss it before local scientific bodies4 ,in #ahig he prepared a paper on ,a ,group of ,hypotheses ,bearing on ,climatic ,changes1 ,jour4 ,geol41 ,vol4 ,v 7#ahig71 to be read at the meeting of the ,british ,association at ,toronto1 basing his conclusions on ,tyndall's determination of the competency of carbon dioxide as an absorber of heat radiated from the earth4 ,he had essentially completed this when a paper by ,arrhenius1 ,on the influence of carbonic acid in the air upon the temperature of the ground1 ,phil4 ,mag41 #ahif1 pp4 #bcg-bgf1 first came to his attention4 ,chamberlin then changed his conservative1 tentative statement of the functions of carbon dioxide to a more sweeping one based on ,arrhenius' very definite quantitative deductions from ,langley's experiments4 ,both ,langley and ,arrhenius were then in the ascendancy of their reputations and seemingly higher authorities could scarcely have been chosen1 nor a finer combination than experiment and physico-mathematical development4 ,arrhenius' deductions were later proved to have been overstrained1 while ,langley's interpretation and even his observations were challenged4 ,chamberlin's latest views are more like his earlier and more conservative statement4 ,footnote #ab3 ,c4 ,g4 ,abbot and ,f4 ,e4 ,fowle3 ,volcanoes and ,climate2 ,smiths4 ,misc4 ,coll41 ,vol4 #fj1 #aiac1 #bd pp4 ,w4 ,j4 ,humphreys3 ,volcanic dust and other factors in the production of climatic and their possible relation to ice ages2 ,bull4 ,mount ,weather ,observatory1 ,vol4 #f1 ,part #a1 #aiac1 #bf pp4 ,also1 ,physics of the ,air1 #aibj4 ,footnote #ac3 ,h4 ,arctowski3 ,the ,pleonian ,cycle of ,climatic ,fluctuations2 ,am4 ,jour4 ,sci41 ,vol4 #db1 #aiaf1 pp4 #bg-cc4 ,see also ,annals of the ,new ,york ,academy of ,sciences1 ,vol4 #bd1 #aiad4 ,footnote #ad3 ,w4 ,koeppen3 ,ueber mehrjaehrige ,perioden der ,witterung ins besondere uezer die ,,ii-jaehrige ,periode der ,temperatur4 ,also1 ,lufttemperaturen ,sonnenflecke und ,vulcanausbrueche2 ,meteorologische ,zeitschrift1 ,vol4 #g1 #aiad1 pp4 #cje-cbh4 ,,chapter ,,iv ,,the ,,solar ,,cyclonic ,,hypothesis ,the progress of science is made up of a vast succession of hypotheses4 ,the majority die in early infancy4 ,a few live and are for a time widely accepted4 ,then some new hypothesis either destroys them completely or shows that1 while they contain elements of truth1 they are not the whole truth4 ,in the previous chapter we have discussed a group of hypotheses of this kind1 and have tried to point out fairly their degree of truth so far as it can yet be determined4 ,in this chapter we shall outline still another hypothesis1 the relation of which to present climatic conditions has been fully developed in ,earth and ,sun2 while its relation to the past will be explained in the present volume4 ,this hypothesis is not supposed to supersede the others1 for so far as they are true they cannot be superseded4 ,it merely seems to explain some of the many conditions which the other hypotheses apparently fail to explain4 ,to suppose that it will suffer a fate more glorious than its predecessors would be presumptuous4 ,the best that can be hoped is that after it has been pruned1 enriched1 and modified1 it may take its place among the steps which finally lead to the goal of truth4 ,in this chapter the new hypothesis will be sketched in broad outline in order that in the rest of this book the reader may appreciate the bearing of all that is said4 ,details of proof and methods of work will be omitted1 since they are given in ,earth and ,sun4 ,for the sake of brevity and clearness the main conclusions will be stated without the qualifications and exceptions which are fully explained in that volume4 ,here it will be necessary to pass quickly over points which depart radically from accepted ideas1 and which therefore must arouse serious question in the minds of thoughtful readers4 ,that1 however1 is a necessary consequence of the attempt which this book makes to put the problem of climate in such form that the argument can be followed by thoughtful students in any branch of knowledge and not merely by specialists4 ,therefore1 the specialist can merely be asked to withhold judgment until he has read all the evidence as given in ,earth and ,sun1 and then to condemn only those parts that are wrong and not the whole argument4 ,without further explanation let us turn to our main problem4 ,in the realm of climatology the most important discovery of the last generation is that variations in the weather depend on variations in the activity of the sun's atmosphere4 ,the work of the great astronomer1 ,newcomb1 and that of the great climatologist1 ,koeppen1 have shown beyond question that the temperature of the earth's surface varies in harmony with variations in the number and area of sunspots4#ae ,the work of ,abbot has shown that the amount of heat radiated from the sun also varies1 and that in general the variations correspond with those of the sunspots1 although there are exceptions1 especially when the spots are fewest4 ,here1 however1 there at once arises a puzzling paradox4 ,the earth certainly owes its warmth to the sun4 ,yet when the sun emits the most energy1 that is1 when sunspots are most numerous1 the earth's surface is coolest4 ,doubtless the earth receives more heat than usual at such times1 and the upper air may be warmer than usual4 ,here we refer only to the air at the earth's surface4 ,another large group of investigators have shown that atmospheric pressure also varies in harmony with the number of sunspots4 ,some parts of the earth's surface have one kind of variation at times of many sunspots and other parts the reverse4 ,these differences are systematic and depend largely on whether the region in question happens to have high atmospheric pressure or low4 ,the net result is that when sunspots are numerous the earth's storminess increases1 and the atmosphere is thrown into commotion4 ,this interferes with the stable planetary winds1 such as the trades of low latitudes and the prevailing westerlies of higher latitudes4 ,instead of these regular winds and the fair weather which they bring1 there is a tendency toward frequent tropical hurricanes in the lower latitudes and toward more frequent and severe storms of the ordinary type in the latitudes where the world's most progressive nations now live4 ,with the change in storminess there naturally goes a change in rainfall4 ,not all parts of the world1 however1 have increased storminess and more abundant rainfall when sunspots are numerous4 ,some parts change in the opposite way4 ,thus when the sun's atmosphere is particularly disturbed1 the contrasts between different parts of the earth's surface are increased4 ,for example1 the northern ,united ,states and southern ,canada become more stormy and rainy1 as appears in ,fig4 #b1 and the same is true of the ,southwest and along the south ,atlantic coast4 ,in a crescent-shaped central area1 however1 extending from ,wyoming through ,missouri to ,nova ,scotia1 the number of storms and the amount of rainfall decrease4 ,illustration3 ,fig4 #b4 ,storminess at sunspot maxima vs4 minima4 7,after ,kullmer47 ,based on nine years' nearest sunspot minima and nine years' nearest sunspot maxima in the three sunspot cycles from #ahhh to #aiah4 ,heavy shading indicates excess of storminess when sunspots are numerous4 ,figures indicate average yearly number of storms by which years of maximum sunspots exceed those of minimum sunspots4 ,the two controlling factors of any climate are the temperature and the atmospheric pressure1 for they determine the winds1 the storms1 and thus the rainfall4 ,a study of the temperature seems to show that the peculiar paradox of a hot sun and a cool earth is due largely to the increased storminess during times of many sunspots4 ,the earth's surface is heated by the rays of the sun1 but most of the rays do not in themselves heat the air as they pass through it4 ,the air gets its heat largely from the heat absorbed by the water vapor which is intimately mingled with its lower portions1 or from the long heat waves sent out by the earth after it has been warmed by the sun4 ,the faster the air moves along the earth's surface the less it becomes heated1 and the more heat it takes away4 ,this sounds like a contradiction1 but not to anyone who has tried to heat a stove in the open air4 ,if the air is still1 the stove rapidly becomes warm and so does the air around it4 ,if the wind is blowing1 the cool air delays the heating of the stove and prevents the surface from ever becoming as hot as it would otherwise4 ,that seems to be what happens on a large scale when sunspots are numerous4 ,the sun actually sends to the earth more energy than usual1 but the air moves with such unusual rapidity that it actually cools the earth's surface a trifle by carrying the extra heat to high levels where it is lost into space4 ,there has been much discussion as to why storms are numerous when the sun's atmosphere is disturbed4 ,many investigators have supposed it was due entirely and directly to the heating of the earth's surface by the sun4 ,this1 however1 needs modification for several reasons4 ,in the first place1 recent investigations show that in a great many cases changes in barometric pressure precede changes in temperature and apparently cause them by altering the winds and producing storms4 ,this is the opposite of what would happen if the effect of solar heat upon the earth's surface were the only agency4 ,in the second place1 if storms were due exclusively to variations in the ordinary solar radiation which comes to the earth as light and is converted into heat1 the solar effect ought to be most pronounced when the center of the sun's visible disk is most disturbed4 ,as a matter of fact the storminess is notably greatest when the edges of the solar disk are most disturbed4 ,these facts and others lead to the conclusion that some agency other than heat must also play some part in producing storminess4 ,the search for this auxiliary agency raises many difficult questions which cannot yet be answered4 ,on the whole the weight of evidence suggests that electrical phenomena of some kind are involved1 although variations in the amount of ultra-violet light may also be important4 ,many investigators have shown that the sun emits electrons4 ,hale has proved that the sun1 like the earth1 is magnetized4 ,sunspots also have magnetic fields the strength of which is often fifty times as great as that of the sun as a whole4 ,if electrons are sent to the earth1 they must move in curved paths1 for they are deflected by the sun's magnetic field and again by the earth's magnetic field4 ,the solar deflection may cause their effects to be greatest when the spots are near the sun's margin2 the terrestrial deflection may cause concentration in bands roughly concentric with the magnetic poles of the earth4 ,these conditions correspond with the known facts4 ,farther than this we cannot yet go4 ,the calculations of ,humphreys seem to indicate that the direct electrical effect of the sun's electrons upon atmospheric pressure is too small to be of appreciable significance in intensifying storms4 ,on the other hand the peculiar way in which activity upon the margins of the sun appears to be correlated not only with atmospheric electricity1 but with barometric pressure1 seems to be equally strong evidence in the other direction4 ,possibly the sun's electrons and its electrical waves produce indirect effects by being converted into heat1 or by causing the formation of ozone and the condensation of water vapor in the upper air4 ,any one of these processes would raise the temperature of the upper air1 for the ozone and the water vapor would be formed there and would tend to act as a blanket to hold in the earth's heat4 ,but any such change in the temperature of the upper air would influence the lower air through changes in barometric pressure4 ,these considerations are given here because the thoughtful reader is likely to inquire how solar activity can influence storminess4 ,moreover1 at the end of this book we shall take up certain speculative questions in which an electrical hypothesis will be employed4 ,for the main portions of this book it makes no difference how the sun's variations influence the earth's atmosphere4 ,the only essential point is that when the solar atmosphere is active the storminess of the earth increases1 and that is a matter of direct observation4 ,let us now inquire into the relation between the small cyclonic vacillations of the weather and the types of climatic changes known as historic pulsations and glacial fluctuations4 ,one of the most interesting results of recent investigations is the evidence that sunspot cycles on a small scale present almost the same phenomena as do historic pulsations and glacial fluctuations4 ,for instance1 when sunspots are numerous1 storminess increases markedly in a belt near the northern border of the area of greatest storminess1 that is1 in southern ,canada and thence across the ,atlantic to the ,north ,sea and ,scandinavia4 7,see ,figs4 #b and #c47 ,corresponding with this is the fact that the evidence as to climatic pulsations in historic times indicates that regions along this path1 for instance ,greenland1 the ,north ,sea region1 and southern ,scandinavia1 were visited by especially frequent and severe storms at the climax of each pulsation4 ,moreover1 the greatest accumulations of ice in the glacial period were on the poleward border of the general regions where now the storms appear to increase most at times of solar activity4 ,illustration3 ,fig4 #c;,a4 ,relative rainfall at times of increasing and decreasing sunspots4 ,heavy shading1 more rain with increasing spots4 ,light shading1 more rain with decreasing spots4 ,no data for unshaded areas4 ,figures indicate percentages of the average rainfall by which the rainfall during periods of increasing spots exceeds or falls short of rainfall during periods of decreasing spots4 ,the excess or deficiency is stated in percentages of the average4 ,rainfall data from ,walker3 ,sunspots and ,rainfall4 ,illustration3 ,fig4 #c;,b4 ,relative rainfall at times of increasing and decreasing sunspots4 ,heavy shading1 more rain with increasing spots4 ,light shading1 more rain with decreasing spots4 ,no data for unshaded areas4 ,figures indicate percentages of the average rainfall by which the rainfall during periods of increasing spots exceeds or falls short of rainfall during periods of decreasing spots4 ,the excess or deficiency is stated in percentages of the average4 ,rainfall data from ,walker3 ,sunspots and ,rainfall4 ,even more clear is the evidence from other regions where storms increase at times of many sunspots4 ,one such region includes the southwestern ,united ,states1 while another is the ,mediterranean region and the semi-arid or desert parts of ,asia farther east4 ,in these regions innumerable ruins and other lines of evidence show that at the climax of each climatic pulsation there was more storminess and rainfall than at present1 just as there now is when the sun is most active4 ,in still earlier times1 while ice was accumulating farther north1 the basins of these semi-arid regions were filled with lakes whose strands still remain to tell the tale of much-increased rainfall and presumable storminess4 ,if we go back still further in geological times to the ,permian glaciation1 the areas where ice accumulated most abundantly appear to be the regions where tropical hurricanes produce the greatest rainfall and the greatest lowering of temperature at times of many sunspots4 ,from these and many other lines of evidence it seems probable that historic pulsations and glacial fluctuations are nothing more than sunspot cycles on a large scale4 ,it is one of the fundamental rules of science to reason from the known to the unknown1 from the near to the far1 from the present to the past4 ,hence it seems advisable to investigate whether any of the climatic phenomena of the past may have arisen from an intensification of the solar conditions which now appear to give rise to similar phenomena on a small scale4 ,the rest of this chapter will be devoted to a resume of certain tentative conclusions which have no bearing on the main part of this book1 but which apply to the closing chapters4 ,there we shall inquire into the periodicity of the climatic phenomena of geological times1 and shall ask whether there is any reason to suppose that the sun's activity has exhibited similar periodicity4 ,this leads to an investigation of the possible causes of disturbances in the sun's atmosphere4 ,it is generally assumed that sunspots1 solar prominences1 the bright clouds known as faculae1 and other phenomena denoting a perturbed state of the solar atmosphere1 are due to some cause within the sun4 ,yet the limitation of these phenomena1 especially the sunspots1 to restricted latitudes1 as has been shown in ,earth and ,sun1 does not seem to be in harmony with an internal solar origin1 even though a banded arrangement may be normal for a rotating globe4 ,the fairly regular periodicity of the sunspots seems equally out of harmony with an internal origin4 ,again1 the solar atmosphere has two kinds of circulation1 one the so-called rice grains1 and the other the spots and their attendant phenomena4 ,now the rice grains present the appearance that would be expected in an atmospheric circulation arising from the loss of heat by the outer part of a gaseous body like the sun4 ,for these reasons and others numerous good thinkers from ,wolf to ,schuster have held that sunspots owe their periodicity to causes outside the sun4 ,the only possible cause seems to be the planets1 acting either through gravitation1 through forces of an electrical origin1 or through some other agency4 ,various new investigations which are described in ,earth and ,sun support this conclusion4 ,the chief difficulty in accepting it hitherto has been that although ,jupiter1 because of its size1 would be expected to dominate the sunspot cycle1 its period of #aa4hf years has not been detected4 ,the sunspot cycle has appeared to average #aa4b years in length1 and has been called the #aa-year cycle4 ,nevertheless1 a new analysis of the sunspot data shows that when attention is concentrated upon the major maxima1 which are least subject to retardation or acceleration by other causes1 a periodicity closely approaching that of ,jupiter is evident4 ,moreover1 when the effects of ,jupiter1 ,saturn1 and the other planets are combined1 they produce a highly variable curve which has an extraordinary resemblance to the sunspot curve4 ,the method by which the planets influence the sun's atmosphere is still open to question4 ,it may be through tides1 through the direct effect of gravitation1 through electro-magnetic forces1 or in some other way4 ,whichever it may be1 the result may perhaps be slight differences of atmospheric pressure upon the sun4 ,such differences may set in motion slight whirling movements analogous to terrestrial storms1 and these presumably gather momentum from the sun's own energy4 ,since the planetary influences vary in strength because of the continuous change in the relative distances and positions of the planets1 the sun's atmosphere appears to be swayed by cyclonic disturbances of varying degrees of severity4 ,the cyclonic disturbances known as sunspots have been proved by ,hale to become more highly electrified as they increase in intensity4 ,at the same time hot gases presumably well up from the lower parts of the solar atmosphere and thereby cause the sun to emit more heat4 ,thus by one means or another1 the earth's atmosphere appears to be set in commotion and cycles of climate are inaugurated4 ,if the preceding reasoning is correct1 any disturbance of the solar atmosphere must have an effect upon the earth's climate4 ,if the disturbance were great enough and of the right nature it might produce a glacial epoch4 ,the planets are by no means the only bodies which act upon the sun1 for that body sustains a constantly changing relation to millions of other celestial bodies of all sizes up to vast universes1 and at all sorts of distances4 ,if the sun and another star should approach near enough to one another1 it is certain that the solar atmosphere would be disturbed much more than at present4 ,here we must leave the cyclonic hypothesis of climate and must refer the reader once more to ,earth and ,sun for fuller details4 ,in the rest of this book we shall discuss the nature of the climatic changes of past times and shall inquire into their relation to the various climatic hypotheses mentioned in the last two chapters4 ,then we shall inquire into the possibility that the solar system has ever been near enough to any of the stars to cause appreciable disturbances of the solar atmosphere4 ,we shall complete our study by investigating the vexed question of why movements of the earth's crust1 such as the uplifting of continents and mountain chains1 have generally occurred at the same time as great climatic fluctuations4 ,this would not be so surprising were it not that the climatic phenomena appear to have consisted of highly complex cycles while the uplift has been a relatively steady movement in one direction4 ,we shall find some evidence that the solar disturbances which seem to cause climatic changes also have a relation to movements of the crust4 ,,footnotes3 ,footnote #ae3 ,the so-called sunspot numbers to which reference is made again and again in this book are based on a system devised by ,wolf and revised by ,a4 ,wolfer4 ,the number and size of the spots are both taken into account4 ,the numbers from #agdi to #aijj may be found in the ,monthly ,weather ,review for ,april1 #aijb1 and from #aija to #aiah in the same journal for #aibj4 ,,chapter ,v ,,the ,,climate ,,of ,,history#af ,we are now prepared to consider the climate of the past4 ,the first period to claim attention is the few thousand years covered by written history4 ,strangely enough1 the conditions during this time are known with less accuracy than are those of geological periods hundreds of times more remote4 ,yet if pronounced changes have occurred since the days of the ancient ,babylonians and since the last of the post-glacial stages1 they are of great importance not only because of their possible historic effects1 but because they bridge the gap between the little variations of climate which are observable during a single lifetime and the great changes known as glacial epochs4 ,only by bridging the gap can we determine whether there is any genetic relation between the great changes and the small4 ,a full discussion of the climate of historic times is not here advisable1 for it has been considered in detail in numerous other publications4#ag ,our most profitable course would seem to be to consider first the general trend of opinion and then to take up the chief objections to each of the main hypotheses4 ,in the hot debate over this problem during recent decades the ideas of geographers seem to have gone through much the same metamorphosis as have those of geologists in regard to the climate of far earlier times4 ,as every geologist well knows1 at the dawn of geology people believed in climatic uniformity--that is1 it was supposed that since the completion of an original creative act there had been no important changes4 ,this view quickly disappeared and was superseded by the hypothesis of progressive cooling and drying1 an hypothesis which had much to do with the development of the nebular hypothesis1 and which has in turn been greatly strengthened by that hypothesis4 ,the discovery of evidence of widespread continental glaciation1 however1 necessitated a modification of this view1 and succeeding years have brought to light a constantly increasing number of glacial1 or at least cool1 periods distributed throughout almost the whole of geological time4 ,moreover1 each year1 almost1 brings new evidence of the great complexity of glacial periods1 epochs1 and stages4 ,thus1 for many decades1 geologists have more and more been led to believe that in spite of surprising uniformity1 when viewed in comparison with the cosmic possibilities1 the climate of the past has been highly unstable from the viewpoint of organic evolution1 and its changes have been of all degrees of intensity4 ,geographers have lately been debating the reality of historic changes of climate in the same way in which geologists debated the reality of glacial epochs and stages4 ,several hypotheses present themselves but these may all be grouped under three headings2 namely1 the hypotheses of 7#a7 progressive desiccation1 7#b7 climatic uniformity1 and 7#c7 pulsations4 ,the hypothesis of progressive desiccation has been widely advocated4 ,in many of the drier portions of the world1 especially between #cj deg4 and #dj deg4 from the equator1 and preeminently in western and central ,asia and in the southwestern ,united ,states1 almost innumerable facts seem to indicate that two or three thousand years ago the climate was distinctly moister than at present4 ,the evidence includes old lake strands1 the traces of desiccated springs1 roads in places now too dry for caravans1 other roads which make detours around dry lake beds where no lakes now exist1 and fragments of dead forests extending over hundreds of square miles where trees cannot now grow for lack of water4 ,still stronger evidence is furnished by ancient ruins1 hundreds of which are located in places which are now so dry that only the merest fraction of the former inhabitants could find water4 ,the ruins of ,palmyra1 in the ,syrian ,desert1 show that it must once have been a city like modern ,damascus1 with one or two hundred thousand inhabitants1 but its water supply now suffices for only one or two thousand4 ,all attempts to increase the water supply have had only a slight effect and the water is notoriously sulphurous1 whereas in the former days1 when it was abundant1 it was renowned for its excellence4 ,hundreds of pages might be devoted to describing similar ruins4 ,some of them are even more remarkable for their dryness than is ,niya1 a site in the ,tarim ,desert of ,chinese ,turkestan4 ,yet there the evidence of desiccation within #bjjj years is so strong that even so careful and conservative a man as ,hann1#ah pronounces it ueberzeugend4 ,a single quotation from scores that might be used will illustrate the conclusions of some of the most careful archaeologists4#ai ,among the regions which were once populous and highly civilized1 but which are now desert and deserted1 there are few which were more closely connected with the beginnings of our own civilization than the desert parts of ,syria and northern ,arabia4 ,it is only of recent years that the vast extent and great importance of this lost civilization has been fully recognized and that attempts have been made to reduce the extent of the unexplored area and to discover how much of the territory which has long been known as desert was formerly habitable and inhabited4 ,the results of the explorations of the last twenty years have been most astonishing in this regard4 ,it has been found that practically all of the wide area lying between the coast range of the eastern ,mediterranean and the ,euphrates1 appearing upon the maps as the ,syrian ,desert1 an area embracing somewhat more than #bj1jjj square miles1 was more thickly populated than any area of similar dimensions in ,england or in the ,united ,states is today if one excludes the immediate vicinity of the large modern cities4 ,it has also been discovered that an enormous desert tract lying to the east of ,palestine1 stretching eastward and southward into the country which we know as ,arabia1 was also a densely populated country4 ,how far these settled regions extended in antiquity is still unknown1 but the most distant explorations in these directions have failed to reach the end of ruins and other signs of former occupation4 ,the traveler who has crossed the settled1 and more or less populous1 coast range of northern ,syria and descended into the narrow fertile valley of the ,orontes1 encounters in any farther journey toward the east an irregular range of limestone hills lying north and south and stretching to the northeast almost halfway to the ,euphrates4 ,these hills are about #b1ejj feet high1 rising in occasional peaks from #c1jjj to #c1ejj feet above sea level4 ,they are gray and unrelieved by any visible vegetation4 ,on ascending into the hills the traveler is astonished to find at every turn remnants of the work of men's hands1 paved roads1 walls which divided fields1 terrace walls of massive structure4 ,presently he comes upon a small deserted and partly ruined town composed of buildings large and small constructed of beautifully wrought blocks of limestone1 all rising out of the barren rock which forms the ribs of the hills4 ,if he mounts an eminence in the vicinity1 he will be still further astonished to behold similar ruins lying in all directions4 ,he may count ten or fifteen or twenty1 according to the commanding position of his lookout4 ,from a distance it is often difficult to believe that these are not inhabited places2 but closer inspection reveals that the gentle hand of time or the rude touch of earthquake has been laid upon every building4 ,some of the towns are better preserved than others2 some buildings are quite perfect but for their wooden roofs which time has removed1 others stand in picturesque ruins1 while others still are level with the ground4 ,on a far-off hilltop stands the ruin of a pagan temple1 and crowning some lofty ridge lie the ruins of a great ,christian monastery4 ,mile after mile of this barren gray country may be traversed without encountering a single human being4 ,day after day may be spent in traveling from one ruined town to another without seeing any green thing save a terebinth tree or two standing among the ruins1 which have sent their roots down into earth still preserved in the foundations of some ancient building4 ,no soil is visible anywhere except in a few pockets in the rock from which it could not be washed by the torrential rains of the wet season2 yet every ruin is surrounded with the remains of presses for the making of oil and wine4 ,only one oasis has been discovered in these high plateaus4 ,passing eastward from this range of hills1 one descends into a gently rolling country that stretches miles away toward the ,euphrates4 ,at the eastern foot of the hills one finds oneself in a totally different country1 at first quite fertile and dotted with frequent villages of flat-roofed houses4 ,here practically all the remains of ancient times have been destroyed through ages of building and rebuilding4 ,beyond this narrow fertile strip the soil grows drier and more barren1 until presently another kind of desert is reached1 an undulating waste of dead soil4 ,few walls or towers or arches rise to break the monotony of the unbroken landscape2 but the careful explorer will find on closer examination that this region was more thickly populated in antiquity even than the hill country to the west4 ,every unevenness of the surface marks the site of a town1 some of them cities of considerable extent4 ,we may draw certain very definite conclusions as to the former conditions of the country itself4 ,there was soil upon the northern hills where none now exists1 for the buildings now show unfinished foundation courses which were not intended to be seen2 the soil in depressions without outlets is deeper than it formerly was2 there are hundreds of olive and wine presses in localities where no tree or vine could now find footing2 and there are hillsides with ruined terrace walls rising one above the other with no sign of earth near them4 ,there was also a large natural water supply4 ,in the north as well as in the south we find the dry beds of rivers1 streams1 and brooks with sand and pebbles and well-worn rocks but no water in them from one year's end to the other4 ,we find bridges over these dry streams and crudely made washing boards along their banks directly below deserted towns4 ,many of the bridges span the beds of streams that seldom or never have water in them and give clear evidence of the great climatic changes that have taken place4 ,there are well heads and well houses1 and inscriptions referring to springs2 but neither wells nor springs exist today except in the rarest instances4 ,many of the houses had their rock-hewn cisterns1 never large enough to have supplied water for more than a brief period1 and corresponding to the cisterns which most of our recent forefathers had which were for convenience rather than for dependence4 ,some of the towns in southern ,syria were provided with large public reservoirs1 but these are not large enough to have supplied water to their original populations4 ,the high plateaus were of course without irrigation2 but there are no signs1 even in the lower flatter country1 that irrigation was ever practiced2 and canals for this purpose could not have completely disappeared4 ,there were forests in the immediate vicinity1 forests producing timbers of great length and thickness2 for in the north and northeast practically all the buildings had wooden roofs1 wooden intermediate floors1 and other features of wood4 ,costly buildings1 such as temples and churches1 employed large wooden beams2 but wood was used in much larger quantities in private dwellings1 shops1 stables1 and barns4 ,if wood had not been plentiful and cheap--which means grown near by--the builders would have adopted the building methods of their neighbors in the south1 who used very little wood and developed the most perfect type of lithic architecture the world has ever seen4 ,and here there exists a strange anomaly3 ,northern ,syria1 where so much wood was employed in antiquity1 is absolutely treeless now2 while in the mountains of southern ,syria1 where wood must have been scarce in antiquity to have forced upon the inhabitants an almost exclusive use of stone1 there are still groves of scrub oak and pine1 and travelers of half a century ago reported large forests of chestnut trees4#bj ,it is perfectly apparent that large parts of ,syria once had soil and forests and springs and rivers1 while it has none of these now1 and that it had a much larger and better distributed rainfall in ancient times than it has now4 ,professor ,butler's careful work is especially interesting because of its contrast to the loose statements of those who believe in climatic uniformity4 ,so far as ,i am aware1 no opponent of the hypothesis of climatic changes has ever even attempted to show by careful statistical analysis that the ancient water supply of such ruins was no greater than that of the present4 ,the most that has been done is to suggest that there may have been sources of water which are now unknown4 ,of course1 this might be true in a single instance1 but it could scarcely be the case in many hundreds or thousands of ruins4 ,although the arguments in favor of a change of climate during the last two thousand years seem too strong to be ignored1 their very strength seems to have been a source of error4 ,a large number of people have jumped to the conclusion that the change which appears to have occurred in certain regions occurred everywhere1 and that it consisted of a gradual desiccation4 ,many observers1 quite as careful as those who believe in progressive desiccation1 point to evidences of aridity in past times in the very regions where the others find proof of moisture4 ,lakes such as the ,caspian ,sea fell to such a low level that parts of their present floors were exposed and were used as sites for buildings whose ruins are still extant4 ,elsewhere1 for instance in the ,tian-,shan ,mountains1 irrigation ditches are found in places where irrigation never seems to be necessary at present4 ,in ,syria and ,north ,africa during the early centuries of the ,christian era the ,romans showed unparalleled activity in building great aqueducts and in watering land which then apparently needed water almost as much as it does today4 ,evidence of this sort is abundant and is as convincing as is the evidence of moister conditions in the past4 ,it is admirably set forth1 for example1 in the comprehensive and ably written monograph of ,leiter on the climate of ,north ,africa4#ba ,the evidence cited there and elsewhere has led many authors strongly to advocate the hypothesis of climatic uniformity4 ,they have done exactly as have the advocates of progressive change1 and have extended their conclusions over the whole world and over the whole of historic times4 ,the hypotheses of climatic uniformity and of progressive change both seem to be based on reliable evidence4 ,they may seem to be diametrically opposed to one another1 but this is only when there is a failure to group the various lines of evidence according to their dates1 and according to the types of climate in which they happen to be located4 ,when the facts are properly grouped in both time and space1 it appears that evidence of moist conditions in the historic ,mediterranean lands is found during certain periods2 for instance1 four or five hundred years before ,christ1 at the time of ,christ1 and #ajjj ,a4 ,d4 ,the other kind of evidence1 on the contrary1 culminates at other epochs1 such as about #abjj ,b4 ,c4 and in the seventh and thirteenth centuries after ,christ4 ,it is also found during the interval from the culmination of a moist epoch to the culmination of a dry one1 for at such times the climate was growing drier and the people were under stress4 ,this was seemingly the case during the period from the second to the fourth centuries of our era4 ,north ,africa and ,syria must then have been distinctly better watered than at present1 as appears from ,butler's vivid description2 but they were gradually becoming drier1 and the natural effect on a vigorous1 competent people like the ,romans was to cause them to construct numerous engineering works to provide the necessary water4 ,the considerations which have just been set forth have led to a third hypothesis1 that of pulsatory climatic changes4 ,according to this1 the earth's climate is not stable1 nor does it change uniformly in one direction4 ,it appears to fluctuate back and forth not only in the little waves which we see from year to year or decade to decade1 but in much larger waves1 which take hundreds of years or even a thousand4 ,these in turn seem to merge into and be imposed on the greater waves which form glacial stages1 glacial epochs1 and glacial periods4 ,at the present time there seems to be no way of determining whether the general tendency is toward aridity or toward glaciation4 ,the seventh century of our era was apparently the driest time during the historic period--distinctly drier than the present--but the thirteenth century was almost equally dry1 and the twelfth or thirteenth before ,christ may have been very dry4 ,the best test of an hypothesis is actual measurements4 ,in the case of the pulsatory hypothesis we are fortunately able to apply this test by means of trees4 ,the growth of vegetation depends on many factors--soil1 exposure1 wind1 sun1 temperature1 rain1 and so forth4 ,in a dry region the most critical factor in determining how a tree's growth shall vary from year to year is the supply of moisture during the few months of most rapid growth4#bb ,the work of ,douglass#bc and others has shown that in ,arizona and ,california the thickness of the annual rings affords a reliable indication of the amount of moisture available during the period of growth4 ,this is especially true when the growth of several years is taken as the unit and is compared with the growth of a similar number of years before or after4 ,where a long series of years is used1 it is necessary to make corrections to eliminate the effects of age1 but this can be done by mathematical methods of considerable accuracy4 ,it is difficult to determine whether the climate at the beginning and end of a tree's life was the same1 but it is easily possible to determine whether there have been pulsations while the tree was making its growth4 ,if a large number of trees from various parts of a given district all formed thick rings at a certain period and then formed thin ones for a hundred years1 after which the rings again become thick1 we seem to be safe in concluding that the trees have lived through a long1 dry period4 ,the full reasons for this belief and details as to the methods of estimating climate from tree growth are given in ,the ,climatic ,factor4 ,the results set forth in that volume may be summarized as follows3 ,during the years #aiaa and #aiab1 under the auspices of the ,carnegie ,institution of ,washington1 measurements were made of the thickness of the rings of growth on the stumps of about #dej sequoia trees in ,california4 ,these trees varied in age from #bej to nearly #cbej years4 ,the great majority were over #ajjj years of age1 seventy-nine were over #bjjj years1 and three over #cjjj4 ,even where only a few trees are available the record is surprisingly reliable1 except where occasional accidents occur4 ,where the number approximates #ajj1 accidental variations are largely eliminated and we may accept the record with considerable confidence4 ,accordingly1 we may say that in ,california we have a fairly accurate record of the climate for #bjjj years and an approximate record for #ajjj years more4 ,the final results of the measurements of the ,california trees are shown in ,fig4 #d1 where the climatic variations for #cjjj years in ,california are indicated by the solid line4 ,the high parts of the line indicate rainy conditions1 the low parts1 dry4 ,an examination of this curve shows that during #cjjj years there have apparently been climatic variations more important than any which have taken place during the past century4 ,in order to bring out the details more clearly1 the more reliable part of the ,california curve1 from #ajj ,b4 ,c4 to the present time1 has been reproduced in ,fig4 #e4 ,this is identical with the corresponding part of ,fig4 #d1 except that the vertical scale is three times as great4 ,illustration3 ,fig4 #d4 ,changes of climate in ,california 7solid line7 and in western and central ,asia 7dotted line74 ,note4 ,the curves of ,figs4 #d and #e are reproduced as published in ,the ,solar ,hypothesis in #aiad4 ,later work1 however1 has indicated that in the ,asiatic curve the dash lines1 which were tentatively inserted in #aiad1 are probably more nearly correct than the dotted lines4 ,still further evidence indicates that the ,asiatic curve is nearly like that of ,california in its main features4 ,the curve of tree growth in ,california seems to be a true representation of the general features of climatic pulsations in the ,mediterranean region4 ,this conclusion was originally based on the resemblance between the solid line of ,fig4 #d1 representing tree growth1 and the dotted line representing changes of climate in the eastern ,mediterranean region as inferred from the study of ruins and of history before any work on this subject had been done in ,america4#bd ,the dotted line is here reproduced for its historical significance as a stage in the study of climatic changes4 ,if it were to be redrawn today on the basis of the knowledge acquired in the last twelve years1 it would be much more like the tree curve4 ,for example1 the period of aridity suggested by the dip of the dotted line about #cjj ,a4 ,d4 was based largely on ,professor ,butler's data as to the paucity of inscriptions and ruins dating from that period in ,syria4 ,in the recent article1 from which a long quotation has been given1 he shows that later work proves that there is no such paucity4 ,on the other hand1 it has accentuated the marked and sudden decay in civilization and population which occurred shortly after #fjj ,a4 ,d4 ,he reached the same conclusion to which the present authors had come on wholly different grounds1 namely1 that the dip in the dotted line about #cjj ,a4 ,d4 is not warranted1 whereas the dip about #fcj ,a4 ,d4 is extremely important4 ,in similar fashion the work of ,stein#be in central ,asia makes it clear that the contrast between the water supply about #bjj ,b4,c4 and in the preceding and following centuries was greater than was supposed on the basis of the scanty evidence available when the dotted line of ,fig4 #d was drawn in #aiaj4 ,illustration3 ,fig4 #e4 ,changes in ,california climate for #bjjj years1 as measured by growth of ,sequoia trees4 ,fig4 #e is the same as the later portion of ,fig4 #d1 except that the vertical scale has been magnified threefold4 ,it seems probable that the dotted line at the right is more nearly correct than the solid line4 ,during the thirty years since the end of the curve the general tendency appears in general to have been somewhat upward4 ,since the curve of the ,california trees is the only continuous and detailed record yet available for the climate of the last three thousand years1 it deserves most careful study4 ,it is especially necessary to determine the degree of accuracy with which the growth of the trees represents 7#a7 the local rainfall and 7#b7 the rainfall of remote regions such as ,palestine4 ,perhaps the best way to determine these matters is the standard mathematical method of correlation coefficients4 ,if two phenomena vary in perfect unison1 as in the case of the turning of the wheels and the progress of an automobile when the brakes are not applied1 the correlation coefficient is #a4jj1 being positive when the automobile goes forward and negative when it goes backward4 ,if there is no relation between two phenomena1 as in the case of the number of miles run by a given automobile each year and the number of chickens hatched in the same period1 the coefficient is zero4 ,a partial relationship where other factors enter into the matter is represented by a coefficient between zero and one1 as in the case of the movement of the automobile and the consumption of gasoline4 ,in this case the relation is very obvious1 but is modified by other factors1 including the roughness and grade of the road1 the amount of traffic1 the number of stops1 the skill of the driver1 the condition and load of the automobile1 and the state of the weather4 ,such partial relationships are the kind for which correlation coefficients are most useful1 for the size of the coefficients shows the relative importance of the various factors4 ,a correlation coefficient four times the probable error1 which can always be determined by a formula well known to mathematicians1 is generally considered to afford evidence of some kind of relation between two phenomena4 ,when the ratio between coefficient and error rises to six1 the relationship is regarded as strong4 ,few people would question that there is a connection between tree growth and rainfall1 especially in a climate with a long summer dry season like that of ,california4 ,but the growth of the trees also depends on their position1 the amount of shading1 the temperature1 insect pests1 blights1 the wind with its tendency to break the branches1 and a number of other factors4 ,moreover1 while rain commonly favors growth1 great extremes are relatively less helpful than more moderate amounts4 ,again1 the roots of a tree may tap such deep sources of water that neither drought nor excessive rain produces much effect for several years4 ,hence in comparing the growth of the huge sequoias with the rainfall we should expect a correlation coefficient high enough to be convincing1 but decidedly below #a4jj4 ,unfortunately there is no record of the rainfall where the sequoias grow1 the nearest long record being that of ,sacramento1 nearly #bjj miles to the northwest and close to sea level instead of at an altitude of about #fjjj feet4 ,applying the method of correlation coefficients to the annual rainfall of ,sacramento and the growth of the sequoias from #ahfc to #aiaj1 we obtain the results shown in ,table #c4 ,the trees of ,section ,a of the table grew in moderately dry locations although the soil was fairly deep1 a condition which seems to be essential to sequoias4 ,in this case1 as in all the others1 the rainfall is reckoned from ,july to ,june1 which practically means from ,october to ,may1 since there is almost no summer rain4 ,thus the tree growth in #ahfa is compared with the rainfall of the preceding rainy season1 #ahfj-ahfa1 or of several preceding rainy seasons as the table indicates4 ---------------------------------------- --------------------------- ,,table #c ,,correlation ,,coefficients ,,between ,,rainfall ,,and ,,growth ,,of ,,sequoias ,,in ,,california#bf 7r7 ,correlation coefficient 7e7 ,probable error 7r_/e7 ,ratio of coefficient to probable error ,a4 ,,sacramento ,,rainfall ,,and ,,growth ,,of #ah ,,sequoias ,,in ,,dry ,,locations1 #ahfa-aiaj 7r7 7e7 7r_/e7 ------ ------ ----- #a year of rainfall -#j4jei -#j4jif #j4f #b years of rainfall #j4bhh -#j4jij #c4b #c years of rainfall #j4egj -#j4jff #h4g #d years of rainfall #j4dgj -#j4jgf #f4b ,b4 ,,sacramento ,,rainfall ,,and ,,growth ,,of #aab ,,sequoias ,,mostly ,,in ,,moist ,,locations1 #ahfa-aiaj #c years of rainfall #j4cdj -#j4jhg #c4i #d years of rainfall #j4cga -#j4jhd #d4e #e years of rainfall #j4cih -#j4jhb #d4i #f years of rainfall #j4dah -#j4jgi #e4c #g years of rainfall #j4dga -#j4jgf #f4b #h years of rainfall 7#j4ebj7 -#j4jga #g4c #i years of rainfall #j4ege -#j4jfe #h4h #aj years of rainfall #j4egg -#j4jfe #h4h ,c4 ,,sacramento ,,rainfall ,,and ,,growth ,,of #hj ,,sequoias ,,in ,,moist ,,locations1 #ahfa-aiaj #aj years of rainfall #j4fje -#j4jfb #i4h ,d4 ,,annual ,,sequoia ,,growth ,,and ,,rainfall ,,of ,,preceding #e ,,years ,,at ,,stations ,,on ,,southern ,,pacific ,,railroad #a ,years #b ,altitude 7feet7 #c ,rainfall 7inches7 #d ,approximate distance from sequoias 7miles7 #a #b #c #d 7r7 7e7 7r_/e7 --------- ---- ----- --- ------ ------ --------- ,sacramento1 #ahfa-aiaj #gj #ai4dj #bjj #j4cih -#j4jha #d4i ,colfax1 #ahga-aiji #bdjj #dh4id #bjj #j4abb -#j4aac #a4a ,summit1 #ahga-aiji #gjjj #dh4jg #bjj #j4adh -#j4aac #a4c ,truckee1 #ahga-aiji #ehjj #bg4ab #bjj #j4cjj -#j4aje #b4i ,boca1 #ahga-aiji #eejj #bj4cd #bjj #j4fjd -#j4jgf #h4j ,winnemucca1 #ahga-aiji #dcjj #h4fe #cjj #j4dib -#j4jhi #e4e ---------------------------------------- --------------------------- ,in the first line of ,section ,a a correlation coefficient of only -#j4jef1 which is scarcely six-tenths of the probable error1 means that there is no appreciable relation between the rainfall of a given season and the growth during the following spring and summer4 ,the roots of the sequoias probably penetrate so deeply that the rain and melted snow of the spring months do not sink down rapidly enough to influence the trees before the growing season comes to an end4 ,the precipitation of two preceding seasons1 however1 has some effect on the trees1 as appears in the second line of ,section ,a1 where the correlation coefficient is #j4bhh1 or #c4b times the probable error4 ,when the rainfall of three seasons is taken into account the coefficient rises to #j4egj1 or #h4g times the probable error1 while with four years of rainfall the coefficient begins to fall off4 ,thus the growth of these eighteen sequoias on relatively dry slopes appears to have depended chiefly on the rainfall of the second and third preceding rainy seasons4 ,the growth in #aijj1 for example1 depended largely on the rainfall in the rainy seasons of #ahig-ahih and #ahih-ahii4 ,section ,b of the table shows that with #aab trees1 growing chiefly in moist depressions where the water supply is at a maximum1 the correlation between growth and rainfall1 #j4egg for ten years' rainfall1 is even higher than with the dry trees4 ,the seepage of the underground water is so slow that not until four years' rainfall is taken into account is the correlation coefficient more than four times the probable error4 ,when only the trees growing in moist locations are employed1 the coefficient between tree growth and the rainfall for ten years rises to the high figure of #j4fje1 or #i4h times the probable error1 as appears in ,section ,c4 ,these figures1 as well as many others not here published1 make it clear that the curve of sequoia growth from #ahfa to #aiaj affords a fairly close indication of the rainfall at ,sacramento1 provided allowance be made for a delay of three to ten years due to the fact that the moisture in the soil gradually seeps down the mountain-sides and only reaches the sequoias after a considerable interval4 ,if a rainfall record were available for the place where the trees actually grow1 the relationship would probably be still closer4 ,the record at ,fresno1 for example1 bears out this conclusion so far as it goes4 ,but as ,fresno lies at a low altitude and its rainfall is of essentially the ,sacramento type1 its short record is of less value than that of ,sacramento4 ,the only rainfall records among the ,sierras at high levels1 where the rainfall and temperature are approximately like those of the sequoia region1 are found along the main line of the ,southern ,pacific railroad4 ,this runs from ,oakland northeastward seventy miles across the open plain to ,sacramento1 then another seventy miles1 as the crow flies1 through ,colfax and over a high pass in the ,sierras at ,summit1 next twenty miles or so down through ,truckee to ,boca1 on the edge of the inland basin of ,nevada1 and on northeastward another #afj miles to ,winnemucca1 where it turns east toward ,ogden and ,salt ,lake ,city4 ,section ,d of ,table #c shows the correlation coefficients between the rainfall along the railroad and the growth of the sequoias4 ,at ,sacramento1 which lies fairly open to winds from the ,pacific and thus represents the general climate of central ,california1 the coefficient is nearly five times the probable error1 thus indicating a real relation to sequoia growth4 ,then among the foothills of the ,sierras at ,colfax1 the coefficient drops till it is scarcely larger than the probable error4 ,it rises rapidly1 however1 as one advances among the mountains1 until at ,boca it attains the high figure of #j4fjd or eight times the probable error1 and continues high in the dry area farther east4 ,in other words the growth of the sequoias is a good indication of the rainfall where the trees grow and in the dry region farther east4 ,in order to determine the degree to which the sequoia record represents the rainfall of other regions1 let us select ,jerusalem for comparison4 ,the reasons for this selection are that ,jerusalem furnishes the only available record that satisfies the following necessary conditions3 7#a7 its record is long enough to be important2 7#b7 it is located fairly near the latitude of the sequoias1 #cb deg4,n versus #cg deg4,n2 7#c7 it is located in a similar type of climate with winter rains and a long dry summer2 7#d7 it lies well above sea level 7#bejj feet7 and somewhat back from the seacoast1 thus approximating although by no means duplicating the condition of the sequoias2 and 7#e7 it lies in a region where the evidence of climatic changes during historic times is strongest4 ,the ideal place for comparison would be the valley in which grow the cedars of ,lebanon4 ,those trees resemble the sequoias to an extraordinary degree1 not only in their location1 but in their great age4 ,some day it will be most interesting to compare the growth of these two famous groups of old trees4 ---------------------------------------- --------------------------- ,,table #d ,,correlation ,,coefficients ,,between ,,rainfall ,,records ,,in ,,california ,,and ,,jerusalem 7r7 ,correlation coefficient 7e7 ,probable error 7r_/e7 ,ratio of coefficient to probable error ,a4 ,,jerusalem ,,rainfall ,,for #c ,,years ,,and ,,various ,,groups ,,of ,,sequoias#bg 7r7 7e7 7r_/e7 ------ ----- --------- #aa trees measured by ,douglass #j4dec -#j4jgh #e4h #hj trees1 moist locations1 ,groups ,,ia1 ,,iia1 ,,iiia1 ,,va #j4ejj -#j4jgc #f4h #aja trees1 #fi in moist locations1 #cb in dry1 ,i1 ,,ii1 ,,iii #j4faf -#j4jfa #aj4a #aab trees1 #hj in moist locations1 #cb in dry1 ,i1 ,,ii1 ,,iii1 ,v #j4fge -#j4jec #ab4g ,b4 ,,rainfall ,,at ,,jerusalem ,,and ,,at ,,stations ,,in ,,california ,,and ,,nevada #a ,altitude 7feet7 #b ,years -- #c years -- -- #e years -- #a #b 7r7 7r_/e7 7r7 7r_/e7 ---- --------- ------ ------- ------ ------- ,sacramento1 #gj #ahfa-aiaj #j4chf #d4g #j4ceb #d4b ,colfax1 #bdjj #ahga-aiji #j4caa #c4a #j4cjh #c4j ,summit1 #gjjj #ahga-aiji #j4jii #j4i #j4bdh #b4c ,truckee1 #ehjj #ahga-aiji #j4bbi #b4b #j4ccg #c4c ,a,boca1 #eejj #ahga-aiji #j4dhb #f4d #j4fag #h4f ,winnemucca1 #dcjj #ahga-aiji #j4bce #b4b #j4bfj #b4d ,san ,bernardino1 #ajej #ahga-aiji #j4bge #b4g #j4agg #a4h ,c4 ,,rainfall ,,for #c ,,years ,,at ,,california ,,and ,,nevada ,,stations1 #ahga-aiji 7r7 7r_/e7 ------ ------- ,sacramento and ,san ,bernardino #j4ffc #aj4g ,san ,bernardino and ,winnemucca #j4bia #b4h ---------------------------------------- --------------------------- ,the correlation coefficients for the sequoia growth and the rainfall at ,jerusalem are given in ,section ,a1 ,table #d4 ,they are so high and so consistent that they scarcely leave room for doubt that where a hundred or more sequoias are employed1 as in ,fig4 #e1 their curve of growth affords a good indication of the fluctuations of climate in western ,asia4 ,the high coefficient for the eleven trees measured by ,douglass suggests that where the number of trees falls as low as ten1 as in the part of ,fig4 #d from #gaj to #hdj ,b4 ,c41 the relation between tree growth and rainfall is still close even when only one year's growth is considered4 ,where the unit is ten years of growth1 as in ,figs4 #d and #e1 the accuracy of the tree curve as a measure of rainfall is much greater than when a single year is used as in ,table #d4 ,when the unit is raised to thirty years1 as in the smoothed part of ,fig4 #d previous to #bdj ,b4 ,c41 even four trees1 as from #ifj to #ajgj1 probably give a fair approximation to the general changes in rainfall1 while a single tree prior to #aaaj ,b4 ,c4 gives a rough indication4 ,table #d shows a peculiar feature in the fact that the correlations of ,section ,a between tree growth and the rainfall of ,jerusalem are decidedly higher than those between the rainfall in the two regions4 ,only at ,sacramento and ,boca are the rainfall coefficients high enough to be conclusive4 ,this1 however1 is not surprising1 for even between ,sacramento and ,san ,bernardino1 only #djj miles apart1 the correlation coefficient for the rainfall by three-year periods is only #aj4g times the probable error1 as appears in ,section ,c of ,table #d1 while between ,san ,bernardino and ,winnemucca #ejj miles away1 the corresponding figure drops to #b4h4 ,it must be remembered that in some respects the growth of the sequoias is a much better record of rainfall than are the records kept by man4 ,the human record is based on the amount of water caught by a little gauge a few inches in diameter4 ,every gust of wind detracts from the accuracy of the record2 a mile away the rainfall may be double what it is at the gauge4 ,each sequoia1 on the other hand1 draws its moisture from an area thousands of times as large as a rain gauge4 ,moreover1 the trees on which ,figs4 #d and #e are based were scattered over an area fifty miles long and several hundred square miles in extent4 ,hence they represent the summation of the rainfall over an area millions of times as large as that of a rain gauge4 ,this fact and the large correlation coefficients between sequoia growth and ,jerusalem rainfall should be considered in connection with the fact that all the coefficients between the rainfall of ,california and ,nevada and that of ,jerusalem are positive4 ,if full records of the complete rainfall of ,california and ,nevada on the one hand and of the eastern ,mediterranean region on the other were available for a long period1 they would probably agree closely4 ,just how widely the sequoias can be used as a measure of the climate of the past is not yet certain4 ,in some regions1 as will shortly be explained1 the climatic changes seem to have been of an opposite character from those of ,california4 ,in others the ,californian or eastern ,mediterranean type of change seems sometimes to prevail but is not always evident4 ,for example1 at ,malta the rainfall today shows a distinct relation to that of ,jerusalem and to the growth of the sequoias4 ,but the correlation coefficient between the rainfall of eight-year periods at ,naples1 a little farther north1 and the growth of the sequoias at the end of the periods is -#j4acb1 or only #a4d times the probable error and much too small to be significant4 ,this is in harmony with the fact that although ,naples has summer droughts1 they are not so pronounced as in ,california and ,palestine1 and the prevalence of storms is much greater4 ,jerusalem receives only #h per cent of its rain in the seven months from ,april to ,october1 and ,sacramento #ac1 while ,malta receives #ca per cent and ,naples #dc4 ,nevertheless1 there is some evidence that in the past the climatic fluctuations of southern ,italy followed nearly the same course as those of ,california and ,palestine4 ,this apparent discrepancy seems to be explained by our previous conclusion that changes of climate are due largely to a shifting of storm tracks4 ,when sunspots are numerous the storms which now prevail in northern ,italy seem to be shifted southward and traverse the ,mediterranean to ,palestine just as similar storms are shifted southward in the ,united ,states4 ,this perhaps accounts for the agreement between the sequoia curve and the agricultural and social history of ,rome from about #djj ,b4 ,c4 to #ajj ,a4 ,d41 as explained in ,world ,power and ,evolution4 ,for our present purposes1 however1 the main point is that since rainfall records have been kept the fluctuations of climate indicated by the growth of the sequoias have agreed closely with fluctuations in the rainfall of the eastern ,mediterranean region4 ,presumably the same was true in the past4 ,in that case1 the sequoia curve not only is a good indication of climatic changes or pulsations in regions of similar climate1 but may serve as a guide to coincident but different changes in regions of other types4 ,an enormous body of other evidence points to the same conclusion4 ,it indicates that while the average climate of the present is drier than that of the past in regions having the ,mediterranean type of winter rains and summer droughts1 there have been pronounced pulsations during historic times so that at certain times there has actually been greater aridity than at present4 ,this conclusion is so important that it seems advisable to examine the only important arguments that have been raised against it1 especially against the idea that the general rainfall of the eastern ,mediterranean was greater in the historic past than at present4 ,the first objection is the unquestionable fact that droughts and famines have occurred at periods which seem on other evidence to have been moister than the present4 ,this argument has been much used1 but it seems to have little force4 ,if the rainfall of a given region averages thirty inches and varies from fifteen to forty-five1 a famine will ensue if the rainfall drops for a few years to the lower limit and does not rise much above twenty for a few years4 ,if the climate of the place changes during the course of centuries1 so that the rainfall averages only twenty inches1 and ranges from seven to thirty-five1 famine will again ensue if the rainfall remains near ten inches for a few years4 ,the ravages of the first famine might be as bad as those of the second4 ,they might even be worse1 because when the rainfall is larger the population is likely to be greater and the distress due to scarcity of food would affect a larger number of people4 ,hence historic records of famines and droughts do not indicate that the climate was either drier or moister than at present4 ,they merely show that at the time in question the climate was drier than the normal for that particular period4 ,the second objection is that deserts existed in the past much as at present4 ,this is not a real objection1 however1 for1 as we shall see more fully1 some parts of the world suffer one kind of change and others quite the opposite4 ,moreover1 deserts have always existed1 and when we talk of a change in their climate we merely mean that their boundaries have shifted4 ,a concrete example of the mistaken use of ancient dryness as proof of climatic uniformity is illustrated by the march of ,alexander from ,india to ,mesopotamia4 ,hedin gives an excellent presentation of the case in the second volume of his ,overland to ,india4 ,he shows conclusively that ,alexander's army suffered terribly from lack of water and provisions4 ,this certainly proves that the climate was dry1 but it by no means indicates that there has been no change from the past to the present4 ,we do not know whether ,alexander's march took place during an especially dry or an especially wet year4 ,in a desert region like ,makran1 in southern ,persia and ,beluchistan1 where the chief difficulties occurred1 the rainfall varies greatly from year to year4 ,we have no records from ,makran1 but the conditions there are closely similar to those of southern ,arizona and ,new ,mexico4 ,in #ahhe and #aije the rainfall for five stations in that region was as follows3 ---------------------------------------- -------------------- ,mean rainfall during period #ahhe #aije since observations began ,yuma1 ,arizona1 #b4gb #aa4da #c4ac ,phoenix1 ,arizona1 #c4gg #ai4gc #g4bg ,tucson1 ,arizona1 #e4bf #bd4ag #aa4ff ,lordsburg1 ,new ,mexico1 #c4ii #ai4ej #h4fb ,el ,paso1 ,texas 7on ,new ,mexico border71 #g4ca #ag4hj #i4jf ---- ----- ----- ,average1 #d4fa #ah4eb #g4ie ---------------------------------------- -------------------- ,these stations are distributed over an area nearly #ejj miles east and west4 ,manifestly a traveler who spent the year #ahhe in that region would have had much more difficulty in finding water and forage than one who traveled in the same places in #aije4 ,during #ahhe the rainfall was #db per cent less than the average1 and during #aije it was #acd per cent more than the average4 ,let us suppose1 for the sake of argument1 that the average rainfall of southeastern ,persia is six inches today and was ten inches in the days of ,alexander4 ,if the rainfall from year to year varied as much in the past in ,persia as it does now in ,new ,mexico and ,arizona1 the rainfall during an ancient dry year1 corresponding in character to #ahhe1 would have been about #e4ge inches4 ,on the other hand1 if we suppose that the rainfall then averaged less than at present1--let us say four inches1--a wet year corresponding to #aije in the ,american deserts might have had a rainfall of about ten inches4 ,this being the case1 it is clear that our estimate of what ,alexander's march shows as to climate must depend largely on whether #cbe ,b4 ,c4 was a wet year or a dry year4 ,inasmuch as we know nothing about this1 we must fall back on the fact that a large army accomplished a journey in a place where today even a small caravan usually finds great difficulty in procuring forage and water4 ,moreover1 elephants were taken #ahj miles across what is now an almost waterless desert1 and yet the old historians make no comment on such a feat which today would be practically impossible4 ,these things seem more in harmony with a change of climate than with uniformity4 ,nevertheless1 it is not safe to place much reliance on them except when they are taken in conjunction with other evidence1 such as the numerous ruins1 which show that ,makran was once far more densely populated than now seems possible4 ,taken by itself1 such incidents as ,alexander's march cannot safely be used either as an argument for or against changes of climate4 ,the third and strongest objection to any hypothesis of climatic changes during historic times is based on vegetation4 ,the whole question is admirably set forth by ,j4 ,w4 ,gregory1#bh who gives not only his own results1 but those of the ablest scholars who have preceded him4 ,his conclusions are important because they represent one of the few cases where a definite statistical attempt has been made to prove the exact condition of the climate of the past4 ,after stating various less important reasons for believing that the climate of ,palestine has not changed1 he discusses vegetation4 ,the following quotation indicates his line of thought4 ,a sentence near the beginning is italicized in order to call attention to the importance which ,gregory and others lay on this particular kind of evidence3 ,some more certain test is necessary than the general conclusions which can be based upon the historical and geographical evidence of the ,bible4 ,in the absence of rain gauge and thermometric records1 the most precise test of climate is given by the vegetation2 and fortunately the palm affords a very delicate test of the past climate of ,palestine and the eastern ,mediterranean4444 ,the date palm has three limits of growth which are determined by temperature2 thus it does not reach full maturity or produce ripe fruit of good quality below the mean annual temperature of #fi deg4,f4 ,the isothermal of #fi deg4 crosses southern ,algeria near ,biskra2 it touches the northern coasts of ,cyrenaica near ,derna and passes ,egypt near the mouth of the ,nile1 and then bends northward along the coast lands of ,palestine4 ,to the north of this line the date palm grows and produces fruit1 which only ripens occasionally1 and its quality deteriorates as the temperature falls below #fi deg44 ,between the isotherms of #fh deg4 and #fd deg41 limits which include northern ,algeria1 most of ,sicily1 ,malta1 the southern parts of ,greece and northern ,syria1 the dates produced are so unripe that they are not edible4 ,in the next cooler zone1 north of the isotherm of #fb deg41 which enters ,europe in southwestern ,portugal1 passes through ,sardinia1 enters ,italy near ,naples1 crosses northern ,greece and ,asia ,minor to the east of ,smyrna1 the date palm is grown only for its foliage1 since it does not fruit4 ,hence at ,benghazi1 on the north ,african coast1 the date palm is fertile1 but produces fruit of poor quality4 ,in ,sicily and at ,algiers the fruit ripens occasionally and at ,rome and ,nice the palm is grown only as an ornamental tree4 ,the date palm therefore affords a test of variations in mean annual temperature of three grades between #fb deg4 and #fi deg44 ,this test shows that the mean annual temperature of ,palestine has not altered since ,old ,testament times4 ,the palm tree now grows dates on the coast of ,palestine and in the deep depression around the ,dead ,sea1 but it does not produce fruit on the highlands of ,judea4 ,its distribution in ancient times1 as far as we can judge from the ,bible1 was exactly the same4 ,it grew at ,jericho1 the city of palm trees 7,deut4 xxxiv3 #c and #b ,chron4 xxviii3 #ae71 and at ,engedi1 on the western shore of the ,dead ,sea 7#b ,chron4 xx3 #b2 ,sirach xxiv3 #ad72 and though the palm does not still live at ,jericho--the last apparently died in #ahch--;its disappearance must be due to neglect1 for the only climatic change that would explain it would be an increase in cold or moisture4 ,in olden times the date palm certainly grew on the highlands of ,palestine2 but apparently it never produced fruit there1 for the ,bible references to the palm are to its beauty and erect growth3 ,the righteous shall flourish like the palm 7,ps4 xcii3 #ab72 ,they are upright as the palm tree 7,jer4 x3 #e72 ,thy stature is like to a palm tree 7,cant4 vii3 #g74 ,it is used as a symbol of victory 7,rev4 vii3 #i71 but never praised as a source of food4 ,dates are not once referred to in the text of the ,bible1 but according to the marginal notes the word translated honey in #b ,chron4 xxxi3 #e may mean dates4444 ,it appears1 therefore1 that the date palm had essentially the same distribution in ,palestine in ,old ,testament times as it has now2 and hence we may infer that the mean temperature was then the same as now4 ,if the climate had been moister and cooler1 the date could not have flourished at ,jericho4 ,if it had been warmer1 the palms would have grown freely at higher levels and ,jericho would not have held its distinction as the city of palm trees4#bi ,in the main ,gregory's conclusions seem to be well grounded1 although even according to his data a change of #b deg4 or #c deg4 in mean temperature would be perfectly feasible4 ,it will be noticed1 however1 that they apply to temperature and not to rainfall4 ,they merely prove that two thousand years ago the mean temperature of ,palestine and the neighboring regions was not appreciably different from what it is today4 ,this1 however1 is in no sense out of harmony with the hypothesis of climatic pulsations4 ,students of glaciation believe that during the last glacial epoch the mean temperature of the earth as a whole was only #e deg4 or #f deg4,c4 lower than at present4 ,if the difference between the climate of today and of the time of ,christ is a tenth as great as the difference between the climate of today and that which prevailed at the culmination of the last glacial epoch1 the change in two thousand years has been of large dimensions4 ,yet this would require a rise of only half a degree ,centigrade in the mean temperature of ,palestine4 ,manifestly1 so slight a change would scarcely be detectable in the vegetation4 ,the slightness of changes in mean temperature as compared with changes in rainfall may be judged from a comparison of wet and dry years in various regions4 ,for example1 at ,berlin between #ahff and #aije the ten most rainy years had an average precipitation of #fgj mm4 and a mean temperature of #i4ae deg4,c4 ,on the other hand1 the ten years of least rainfall had an average of #dhc mm4 and a mean temperature of #i4ce deg44 ,in other words1 a difference of #acg mm41 or #ci per cent1 in rainfall was accompanied by a difference of only #j4b deg4,c4 in temperature4 ,such contrasts between the variability of mean rainfall and mean temperature are observable not only when individual years are selected1 but when much longer periods are taken4 ,for instance1 in the western ,gulf region of the ,united ,states the two inland stations of ,vicksburg1 ,mississippi1 and ,shreveport1 ,louisiana1 and the two maritime stations of ,new ,orleans1 ,louisiana1 and ,galveston1 ,texas1 lie at the margins of an area about #djj miles long4 ,during the ten years from #ahge to #ahhd their rainfall averaged #ei4d inches1#cj while during the ten years from #ahij to #ahii it averaged only #db4d inches4 ,even in a region so well watered as the ,gulf ,states1 such a change--#dj per cent more in the first decade than in the second--is important1 and in drier regions it would have a great effect on habitability4 ,yet in spite of the magnitude of the change the mean temperature was not appreciably different1 the average for the four stations being #fg4cf deg4,f4 during the more rainy decade and #ff4id deg4,f4 during the less rainy decade--a difference of only #j4db deg4,f4 ,it is worth noticing that in this case the wetter period was also the warmer1 whereas in ,berlin it was the cooler4 ,this is probably because a large part of the moisture of the ,gulf ,states is brought by winds having a southerly component4 ,similar relationships are apparent in other places4 ,we select ,jerusalem because we have been discussing ,palestine4 ,at the time of writing1 the data available in the ,quarterly ,journal of the ,palestine ,exploration ,fund cover the years from #ahhb-ahii and #aijc-aiji4 ,among these twenty-five years the thirteen which had most rain had an average of #cd4a inches and a temperature of #fb4jd deg4,f4 ,the twelve with least rain had #bd4d inches and a temperature of #fb4dd deg44 ,a difference of #dj per cent in rainfall was accompanied by a difference of only #j4d deg4,f4 in temperature4 ,the facts set forth in the preceding paragraphs seem to show that extensive changes in precipitation and storminess can take place without appreciable changes of mean temperature4 ,if such changed conditions can persist for ten years1 as in one of our examples1 there is no logical reason why they cannot persist for a hundred or a thousand4 ,the evidence of changes in climate during the historic period seems to suggest changes in precipitation much more than in temperature4 ,hence the strongest of all the arguments against historic changes of climate seems to be of relatively little weight1 and the pulsatory hypothesis seems to be in accord with all the known facts4 ,before the true nature of climatic changes1 whether historic or geologic1 can be rightly understood1 another point needs emphasis4 ,when the pulsatory hypothesis was first framed1 it fell into the same error as the hypotheses of uniformity and of progressive change--that is1 the assumption was made that the whole world is either growing drier or moister with each pulsation4 ,a study of the ruins of ,yucatan1 in #aiab1 and of ,guatemala1 in #aiac1 as is explained in ,the ,climatic ,factor1 has led to the conclusion that the climate of those regions has changed in the opposite way from the changes which appear to have taken place in the desert regions farther south4 ,these ,maya ruins in ,central ,america are in many cases located in regions of such heavy rainfall1 such dense forests1 and such malignant fevers that habitation is now practically impossible4 ,the land cannot be cultivated except in especially favorable places4 ,the people are terribly weakened by disease and are among the lowest in ,central ,america4 ,only a hundred miles from the unhealthful forests we find healthful areas1 such as the coasts of ,yucatan and the plateau of ,guatemala4 ,here the vast majority of the population is gathered1 the large towns are located1 and the only progressive people are found4 ,nevertheless1 in the past the region of the forests was the home of by far the most progressive people who are ever known to have lived in ,america previous to the days of ,columbus4 ,they alone brought to high perfection the art of sculpture2 they were the only ,american people who invented the art of writing4 ,it seems scarcely credible that such a people would have lived in the worst possible habitat when far more favored regions were close at hand4 ,therefore it seems as if the climate of eastern ,guatemala and ,yucatan must have been relatively dry at some past time4 ,the ,maya chronology and traditions indicate that this was probably at the same time when moister conditions apparently prevailed in the subarid or desert portions of the ,united ,states and ,asia4 ,fig4 #c shows that today at times of many sunspots there is a similar opposition between a tendency toward storminess and rain in subtropical regions and toward aridity in low latitudes near the heat equator4 ,thus our final conclusion is that during historic times there have been pulsatory changes of climate4 ,these changes have been of the same type in regions having similar kinds of climate1 but of different and sometimes opposite types in places having diverse climates4 ,as to the cause of the pulsations1 they cannot have been due to the precession of the equinoxes nor apparently to any allied astronomical cause1 for the time intervals are too short and too irregular4 ,they cannot have been due to changes in the percentage of carbon dioxide in the atmosphere1 for not even the strongest believers in the climatic efficacy of that gas hold that its amount could fluctuate in any such violent way as would be necessary to explain the pulsations shown in the ,california curve of tree growth4 ,volcanic activity seems more probable as at least a partial cause1 and it would be worth while to investigate the matter more fully4 ,nevertheless1 it can apparently be only a minor cause4 ,in the first place1 the main effect of a cloud of dust is to alter the temperature1 but ,gregory's summary of the palm and the vine shows that variations in temperature are apparently of very slight importance during historic times4 ,again1 ruins on the bottoms of enclosed salt lakes1 old beaches now under the water1 and signs of irrigation ditches where none are now needed indicate a climate drier than the present4 ,volcanic dust1 however1 cannot account for such a condition1 for at present the air seems to be practically free from such dust for long periods4 ,thus we now experience the greatest extreme which the volcanic hypothesis permits in one direction1 but there have been greater extremes in the same direction4 ,the thermal solar hypothesis is likewise unable to explain the observed phenomena1 for neither it nor the volcanic hypothesis offers any explanation of why the climate varies in one way in ,mediterranean climates and in an opposite way in regions near the heat equator4 ,this leaves the cyclonic hypothesis4 ,it seems to fit the facts1 for variations in cyclonic storms cause some regions to be moister and others drier than usual4 ,at the same time the variations in temperature are slight1 and are apparently different in different regions1 some places growing warm when others grow cool4 ,in the next chapter we shall study this matter more fully1 for it can best be appreciated by examining the course of events in a specific century4 ,,footnotes3 ,footnote #af3 ,much of this chapter is taken from ,the ,solar ,hypothesis of ,climatic ,changes2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #be1 #aiad4 ,footnote #ag3 ,ellsworth ,huntington3 ,explorations in ,turkestan1 #aije2 ,the ,pulse of ,asia1 #aijg2 ,palestine and ,its ,transformation1 #aiaa2 ,the ,climatic ,factor1 #aiae2 ,world ,power and ,evolution1 #aiai4 ,footnote #ah3 ,j4 ,hann3 ,klimatologie1 ,vol4 #a1 #aijh1 p4 #ceb4 ,footnote #ai3 ,h4 ,c4 ,butler3 ,desert ,syria1 the ,land of a ,lost ,civilization2 ,geographical ,review1 ,feb41 #aibj1 pp4 #gg-ajh4 ,footnote #bj3 ,this is due to the fact that where these forests occur1 in ,gilead for example1 the mountains to the west break down1 so that the west winds with water from the ,mediterranean are able to reach the inner range without having lost all their water4 ,it is one of the misfortunes of ,syria that its mountains generally rise so close to the sea that they shut off rainfall from the interior and cause the rain to fall on slopes too steep for easy cultivation4 ,footnote #ba3 ,h4 ,leiter3 ,die ,frage der ,klimaanderung waherend geschichtlicher ,zeit in ,nordafrika4 ,abhandl4 ,k4 ,k4 ,geographischen ,gesellschaft1 ,wien1 #aiji1 p4 #adc4 ,footnote #bb3 ,a most careful and convincing study of this problem is embodied in an article by ,j4 ,w4 ,smith3 ,the ,effects of ,weather upon the ,yield of ,corn2 ,monthly ,weather ,review1 ,vol4 #db1 #aiad1 pp4 #gh-ib4 ,on the basis of the yield of corn in ,ohio for #fj years and in other states for shorter periods1 he shows that the rainfall of ,july has almost as much influence on the crop as has the rainfall of all other months combined4 ,see his ,agricultural ,meteorology1 ,new ,york1 #aibj4 ,footnote #bc3 ,see chapter by ,a4 ,e4 ,douglass in ,the ,climatic ,factor2 and his book on ,climatic ,cycles and ,tree-,growth2 ,carnegie ,inst41 #aiai4 ,also article by ,m4 ,n4 ,stewart3 ,the ,relation of ,precipitation to ,tree ,growth1 in the ,monthly ,weather ,review1 ,vol4 #da1 #aiac4 ,footnote #bd3 ,the dotted line is taken from ,palestine and ,its ,transformation1 pp4 #cbg and #djc4 ,footnote #be3 ,m4 ,a4 ,stein3 ,ruins of ,desert ,cathay1 ,london1 #aiab4 ,footnote #bf3 ,in the preparation and interpretation of this table the help of ,mr4 ,g4 ,b4 ,cressey is gratefully acknowledged4 ,footnote #bg3 ,for the tree data used in these comparisons1 see ,the ,climatic ,factor ,p4 #cbh1 and ,a4 ,e4 ,douglass3 ,climatic ,cycles and ,tree ,growth1 p4 #abc4 ,footnote ,a3 ,one year interpolated4 ,footnote #bh3 ,j4 ,w4 ,gregory3 ,is the ,earth ,drying ,up8 ,geog4 ,jour41 ,vol4 #dc1 #aiad1 pp4 #adh-agb and #bic-cah4 ,footnote #bi3 ,geog4 ,jour41 ,vol4 #dc1 pp4 #aei-afa4 ,footnote #cj3 ,see ,a4 ,j4 ,henry3 ,secular ,variation of ,precipitation in the ,united ,states2 ,bull4 ,am4 ,geog4 ,soc41 ,vol4 #df1 #aiad1 pp4 #aib-bja4 ,,chapter ,,vi ,,the ,,climatic ,,stress ,,of ,,the ,,fourteenth ,,century ,in order to give concreteness to our picture of the climatic pulsations of historic times let us take a specific period and see how its changes of climate were distributed over the globe and how they are related to the little changes which now take place in the sunspot cycle4 ,we will take the fourteenth century of the ,christian era1 especially the first half4 ,this period is chosen because it is the last and hence the best known of the times when the climate of the earth seems to have taken a considerable swing toward the conditions which now prevail when the sun is most active1 and which1 if intensified1 would apparently lead to glaciation4 ,it has already been discussed in ,world ,power and ,evolution1 but its importance and the fact that new evidence is constantly coming to light warrant a fuller discussion4 ,to begin with ,europe2 according to the careful account of ,pettersson#ca the fourteenth century shows a record of extreme climatic variations4 ,in the cold winters the rivers ,rhine1 ,danube1 ,thames1 and ,po were frozen for weeks and months4 ,on these cold winters there followed violent floods1 so that the rivers mentioned inundated their valleys4 ,such floods are recorded in #ee summers in the #adth century4 ,there is1 of course1 nothing astonishing in the fact that the inundations of the great rivers of ,europe were more devastating #fjj to #gjj years ago than in our days1 when the flow of the rivers has been regulated by canals1 locks1 etc42 but still the inundations in the #acth and #adth centuries must have surpassed everything of that kind which has occurred since then4 ,in #acdb the waters of the ,rhine rose so high that they inundated the city of ,mayence and the ,cathedral usque ad cingulum hominis4 ,the walls of ,cologne were flooded so that they could be passed by boats in ,july4 ,this occurred also in #acgd in the midst of the month of ,february1 which is of course an unusual season for disasters of the kind4 ,again in other years the drought was so intense that the same rivers1 the ,danube1 ,rhine1 and others1 nearly dried up1 and the ,rhine could be forded at ,cologne4 ,this happened at least twice in the same century4 ,there is one exceptional summer of such evil record that centuries afterwards it was spoken of as the old hot summer of #aceg4 ,pettersson goes on to speak of two oceanic phenomena on which the old chronicles lay greater stress than on all others3 ,the first is the great storm-floods on the coast of the ,north ,sea and the ,baltic1 which occurred so frequently that not less than nineteen floods of a destructiveness unparalleled in later times are recorded from the #adth century4 ,the coastline of the ,north ,sea was completely altered by these floods4 ,thus on ,january #af1 #acjj1 half of the island ,heligoland and many other islands were engulfed by the sea4 ,the same fate overtook the island of ,borkum1 torn into several islands by the storm-flood of ,january #af1 which remoulded the ,frisian ,islands into their present shape1 when also ,wendingstadt1 on the island of ,sylt1 and ,thiryu parishes were engulfed4 ,this flood is known under the name of the great man-drowning4 ,the coasts of the ,baltic also were exposed to storm-floods of unparalleled violence4 ,on ,november #a1 #acjd1 the island of ,ruden was torn asunder from ,rugen by the force of the waves4 ,time does not allow me to dwell upon individual disasters of this kind1 but it will be well to note that of the nineteen great floods on record eighteen occurred in the cold season between the autumnal and vernal equinoxes4 ,the second remarkable phenomenon mentioned by the chronicles is the freezing of the entire ,baltic1 which occurred many times during the cold winters of these centuries4 ,on such occasions it was possible to travel with carriages over the ice from ,sweden to ,bornholm and from ,denmark to the ,german coast 7,lubeck71 and in some cases even from ,gotland to the coast of ,estland4 ,norlind#cb says that the only authentic accounts of the complete freezing of the ,baltic in the neighborhood of the ,kattegat are in the years #abif1 #acjf1 #acbc1 and #adjh4 ,of these #abif is much the most uncertain1 while #acbc was the coldest year ever recorded1 as appears from the fact that horses and sleighs crossed regularly from ,sweden to ,germany on the ice4 ,not only central ,europe and the shores of the ,north ,sea were marked by climatic stress during the fourteenth century1 but ,scandinavia also suffered4 ,as ,pettersson puts it3 ,on examining the historic 7data7 from the last centuries of the ,middle ,ages1 ,dr4 ,bull of ,christiania has come to the conclusion that the decay of the ,norwegian kingdom was not so much a consequence of the political conditions at that time1 as of the frequent failures of the harvest so that corn wheat for bread had to be imported from ,luebeck1 ,rostock1 ,wismar and so forth4 ,the ,hansa ,union undertook the importation and obtained political power by its economic influence4 ,the ,norwegian land-owners were forced to lower their rents4 ,the population decreased and became impoverished4 ,the revenue sank #fj to #gj per cent4 ,even the income from ,church property decreased4 ,in #acfg corn was imported from ,luebeck to a value of one-half million kroner4 ,the trade balance inclined to the disadvantage of ,norway whose sole article of export at that time was dried fish4 7,the production of fish increased enormously in the ,baltic regions off south ,sweden because of the same changes which were influencing the lands1 but this did not benefit ,norway47 ,dr4 ,bull draws a comparison with the conditions described in the ,sagas when ,nordland at the ,arctic ,circle produced enough corn to feed the inhabitants of the country4 ,at the time of ,asbjoern ,selsbane the chieftains in ,trondhenaes still farther north in latitude #fi deg4 grew so much corn that they did not need to go southward to buy corn unless three successive years of dearth had occurred4 ,the province of ,trondheim exported wheat to ,iceland and so forth4 ,probably the turbulent political state of ,scandinavia at the end of the ,middle ,ages was in a great measure due to unfavorable climatic conditions1 which lowered the standard of life1 and not entirely to misgovernment and political strife as has hitherto been taken for granted4 ,during this same unfortunate first half of the fourteenth century ,england also suffered from conditions which1 if sufficiently intensified1 might be those of a glacial period4 ,according to ,thorwald ,rogers#cc the severest famine ever experienced in ,england was that of #acae-acaf1 and the next worst was in #acba4 ,in fact1 from #acjh to #acbb great scarcity of food prevailed most of the time4 ,other famines of less severity occurred in #acea and #acfi4 ,the same cause was at work in all these cases1 says ,rogers1 incessant rain1 and cold1 stormy summers4 ,it is said that the inclemency of the seasons affected the cattle1 and that numbers perished from disease and want4 ,after the bad harvest of #acae the price of wheat1 which was already high1 rose rapidly1 and in ,may1 #acaf1 was about five times the average4 ,for a year or more thereafter it remained at three or four times the ordinary level4 ,the severity of the famine may be judged from the fact that previous to the ,great ,war the most notable scarcity of wheat in modern ,england and the highest relative price was in ,december1 #ahjj4 ,at that time wheat cost nearly three times the usual amount1 instead of five as in #acaf4 ,during the famine of the early fourteenth century it is said that people were reduced to subsist upon roots1 upon horses and dogs1 and stories are told of even more terrible acts by reason of the extreme famine4 ,the number of deaths was so great that the price of labor suffered a permanent rise of at least #aj per cent4 ,there simply were not people enough left among the peasants to do the work demanded by the more prosperous class who had not suffered so much4 ,after the famine came drought4 ,the year #acbe appears to have been peculiarly dry1 and #acca1 #acdd1 #acfb1 #acgd1 and #acgg were also dry4 ,in general these conditions do little harm in ,england4 ,they are of interest chiefly as showing how excessive rain and drought are apt to succeed one another4 ,these facts regarding northern and central ,europe during the fourteenth century are particularly significant when compared with the conclusions which we have drawn in ,earth and ,sun from the growth of trees in ,germany and from the distribution of storms4 ,a careful study of all the facts shows that we are dealing with two distinct types of phenomena4 ,in the first place1 the climate of central ,europe seems to have been peculiarly continental during the fourteenth century4 ,the winters were so cold that the rivers froze1 and the summers were so wet that there were floods every other year or oftener4 ,this seems to be merely an intensification of the conditions which prevail at the present time during periods of many sunspots1 as indicated by the growth of trees at ,eberswalde in ,germany and by the number of storms in winter as compared with summer4 ,the prevalence of droughts1 especially in the spring1 is also not inconsistent with the existence of floods at other seasons1 for one of the chief characteristics of a continental climate is that the variations from one season to another are more marked than in oceanic climates4 ,even the summer droughts are typically continental1 for when continental conditions prevail1 the difference between the same season in different years is extreme1 as is well illustrated in ,kansas4 ,it must always be remembered that what causes famine is not so much absolute dryness as a temporary diminution of the rainfall4 ,the second type of phenomena is peculiarly oceanic in character4 ,it consists of two parts1 both of which are precisely what would be expected if a highly continental climate prevailed over the land4 ,in the first place1 at certain times the cold area of high pressure1 which is the predominating characteristic of a continent during the winter1 apparently spread out over the neighboring oceans4 ,under such conditions an inland sea1 such as the ,baltic1 would be frozen1 so that horses could cross the ice even in the ,far ,west4 ,in the second place1 because of the unusually high pressure over the continent1 the barometric gradients apparently became intensified4 ,hence at the margin of the continental high-pressure area the winds were unusually strong and the storms of corresponding severity4 ,some of these storms may have passed entirely along oceanic tracks1 while others invaded the borders of the land1 and gave rise to the floods and to the wearing away of the coast described by ,pettersson4 ,turning now to the east of ,europe1 ,brueckner's#cd study of the ,caspian ,sea shows that that region as well as western ,europe was subject to great climatic vicissitudes in the first half of the fourteenth century4 ,in #acjf-acjg the ,caspian ,sea1 after rising rapidly for several years1 stood thirty-seven feet above the present level and it probably rose still higher during the succeeding decades4 ,at least it remained at a high level1 for ,hamdulla1 the ,persian1 tells us that in #acbe a place called ,aboskun was under water4#ce ,still further east the inland lake of ,lop ,nor also rose at about this time4 ,according to a ,chinese account the ,dragon ,town on the shore of ,lop ,nor was destroyed by a flood4 ,from ,himley's translation it appears that the level of the lake rose so as to overwhelm the city completely4 ,this would necessitate the expansion of the lake to a point eighty miles east of ,lulan1 and fully fifty from the present eastern end of the ,kara ,koshun marsh4 ,the water would have to rise nearly1 or quite1 to a strand which is now clearly visible at a height of twelve feet above the modern lake or marsh4 ,in ,india the fourteenth century was characterized by what appears to have been the most disastrous drought in all history4 ,apparently the decrease in rainfall here was as striking as the increase in other parts of the world4 ,no statistics are available but we are told that in the great famine which began in #acdd even the ,mogul emperor was unable to obtain the necessaries of life for his household4 ,no rain worth mentioning fell for years4 ,in some places the famine lasted three or four years1 and in some twelve1 and entire cities were left without an inhabitant4 ,in a later famine1 #agfi-aggj1 which occurred in ,bengal shortly after the foundation of ,british rule in ,india1 but while the native officials were still in power1 a third of the population1 or ten out of thirty millions1 perished4 ,the famine in the first half of the fourteenth century seems to have been far worse4 ,these ,indian famines were apparently due to weak summer monsoons caused presumably by the failure of central ,asia to warm up as much as usual4 ,the heavier snowfall1 and the greater cloudiness of the summer there1 which probably accompanied increased storminess1 may have been the reason4 ,the ,new ,world as well as the ,old appears to have been in a state of climatic stress during the first half of the fourteenth century4 ,according to ,pettersson1 ,greenland furnishes an example of this4 ,at first the inhabitants of that northland were fairly prosperous and were able to approach from ,iceland without much hindrance from the ice4 ,today the ,north ,atlantic ,ocean northeast of ,iceland is full of drift ice much of the time4 ,the border of the ice varies from season to season1 but in general it extends westward from ,iceland not far from the ,arctic circle and then follows the coast of ,greenland southward to ,cape ,farewell at the southern tip and around to the western side for fifty miles or more4 ,except under exceptional circumstances a ship cannot approach the coast until well northward on the comparatively ice-free west coast4 ,in the old ,sagas1 however1 nothing is said of ice in this region4 ,the route from ,iceland to ,greenland is carefully described4 ,in the earliest times it went from ,iceland a trifle north of west so as to approach the coast of ,greenland after as short an ocean passage as possible4 ,then it went down the coast in a region where approach is now practically impossible because of the ice4 ,at that time this coast was icy close to the shore1 but there is no sign that navigation was rendered difficult as is now the case4 ,today no navigator would think of keeping close inland4 ,the old route also went north of the island on which ,cape ,farewell is located1 although the narrow channel between the island and the mainland is now so blocked with ice that no modern vessel has ever penetrated it4 ,by the thirteenth century1 however1 there appears to have been a change4 ,in the ,kungaspegel or ,kings' ,mirror1 written at that time1 navigators are warned not to make the east coast too soon on account of ice1 but no new route is recommended in the neighborhood of ,cape ,farewell or elsewhere4 ,finally1 however1 at the end of the fourteenth century1 nearly #aej years after the ,kungaspegel1 the old sailing route was abandoned1 and ships from ,iceland sailed directly southwest to avoid the ice4 ,as ,pettersson says3 444 ,at the end of the thirteenth and the beginning of the fourteenth century the ,european civilization in ,greenland was wiped out by an invasion of the aboriginal population4 ,the colonists in the ,vesterbygd were driven from their homes and probably migrated to ,america leaving behind their cattle in the fields4 ,so they were found by ,ivar ,bardsson1 steward to the ,bishop of ,gardar1 in his official journey thither in #acdb4 ,the ,eskimo invasion must not be regarded as a common raid4 ,it was the transmigration of a people1 and like other big movements of this kind was impelled by altered conditions of nature1 in this case the alterations of climate caused by or which caused8 the advance of the ice4 ,for their hunting and fishing the ,eskimos require an at least partially open arctic sea4 ,the seal1 their principal prey1 cannot live where the surface of the sea is entirely frozen over4 ,the cause of the favorable conditions in the ,viking-age was1 according to my hypothesis1 that the ice then melted at a higher latitude in the arctic seas4 ,the ,eskimos then lived further north in ,greenland and ,north ,america4 ,when the climate deteriorated and the sea which gave them their living was closed by ice the ,eskimos had to find a more suitable neighborhood4 ,this they found in the land colonized by the ,norsemen whom they attacked and finally annihilated4 ,finally1 far to the south in ,yucatan the ancient ,maya civilization made its last flickering effort at about this time4 ,not much is known of this but in earlier periods the history of the ,mayas seems to have agreed quite closely with the fluctuations in climate4#cf ,among the ,mayas1 as we have seen1 relatively dry periods were the times of greatest progress4 ,let us turn now to ,fig4 #c once more and compare the climatic conditions of the fourteenth century with those of periods of increasing rainfall4 ,southern ,england1 ,ireland1 and ,scandinavia1 where the crops were ruined by extensive rain and storms in summer1 are places where storminess and rainfall now increase when sunspots are numerous4 ,central ,europe and the coasts of the ,north ,sea1 where flood and drought alternated1 are regions which now have relatively less rain when sunspots increase than when they diminish4 ,however1 as appears from the trees measured by ,douglass1 the winters become more continental and hence cooler1 thus corresponding to the cold winters of the fourteenth century when people walked on the ice from ,scandinavia to ,denmark4 ,when such high pressure prevails in the winter1 the total rainfall is diminished1 but nevertheless the storms are more severe than usual1 especially in the spring4 ,in southeastern ,europe1 the part of the area whence the ,caspian derives its water1 appears to have less rainfall during times of increasing sunspots than when sunspots are few1 but in an equally large area to the south1 where the mountains are higher and the run-off of the rain is more rapid1 the reverse is the case4 ,this seems to mean that a slight diminution in the water poured in by the ,volga would be more than compensated by the water derived from ,persia and from the ,oxus and ,jaxartes rivers1 which in the fourteenth century appear to have filled the ,sea of ,aral and overflowed in a large stream to the ,caspian4 ,still farther east in central ,asia1 so far as the records go1 most of the country receives more rain when sunspots are many than when they are few1 which would agree with what happened when the ,dragon ,town was inundated4 ,in ,india1 on the contrary1 there is a large area where the rainfall diminishes at times of many sunspots1 thus agreeing with the terrible famine from which the ,moguls suffered so severely4 ,in the western hemisphere1 ,greenland1 ,arizona1 and ,california are all parts of the area where the rain increases with many sunspots1 while ,yucatan seems to lie in an area of the opposite type4 ,thus all the evidence seems to show that at times of climatic stress1 such as the fourteenth century1 the conditions are essentially the same as those which now prevail at times of increasing sunspots4 ,as to the number of sunspots1 there is little evidence previous to about #agej4 ,yet that little is both interesting and important4 ,although sunspots have been observed with care in ,europe only a little more than three centuries1 the ,chinese have records which go back nearly to the beginning of the ,christian era4 ,of course the records are far from perfect1 for the work was done by individuals and not by any great organization which continued the same methods from generation to generation4 ,the mere fact that a good observer happened to use his smoked glass to advantage may cause a particular period to appear to have an unusual number of spots4 ,on the other hand1 the fact that such an observer finds spots at some times and not at others tends to give a valuable check on his results1 as does the comparison of one observer's work with that of another4 ,hence1 in spite of many and obvious defects1 most students of the problem agree that the ,chinese record possesses much value1 and that for a thousand years or more it gives a fairly true idea of the general aspect of the sun4 ,in the ,chinese records the years with many spots fall in groups1 as would be expected1 and are sometimes separated by long intervals4 ,certain centuries appear to have been marked by unusual spottedness4 ,the most conspicuous of these is the fourteenth1 when the years #acgj to #ache were particularly noteworthy1 for spots large enough to be visible to the naked eye covered the sun much of the time4 ,hence ,wolf1#cg who has made an exhaustive study of the matter1 concludes that there was an absolute maximum of spots about #acgb4 ,while this date is avowedly open to question1 the great abundance of sunspots at that time makes it probable that it cannot be far wrong4 ,if this is so1 it seems that the great climatic disturbances of which we have seen evidence in the fourteenth century occurred at a time when sunspots were increasing1 or at least when solar activity was under some profoundly disturbing influence4 ,thus the evidence seems to show not merely that the climate of historic times has been subject to important pulsations1 but that those pulsations were magnifications of the little climatic changes which now take place in sunspot cycles4 ,the past and the present are apparently a unit except as to the intensity of the changes4 ,,footnotes3 ,footnote #ca3 ,o4 ,pettersson3 ,the connection between hydrographical and meteorological phenomena2 ,quarterly ,journal of the ,royal ,meteorological ,society1 ,vol4 #ch1 pp4 #agd-age4 ,footnote #cb3 ,a4 ,norlind3 ,einige ,bemerkungen ueber das ,klima der historischen ,zeit nebst einem ,verzeichnis mittelaltlicher ,witterungs erscheinungen2 ,lunds ,univ4 ,arsskrift1 ,n4 ,f41 ,vol4 #aj1 #aiad1 #ec pp4 ,footnote #cc3 ,thorwald ,rogers3 ,a ,history of ,agriculture and ,prices in ,england4 ,footnote #cd3 ,e4 ,brueckner3 ,klimaschwankungen seit #agjj1 ,vienna1 #ahia4 ,footnote #ce3 ,for a full discussion of the changes in the ,caspian ,sea1 see ,the ,pulse of ,asia1 pp4 #cbi-ceh4 ,footnote #cf3 ,s4 ,q4 ,morley3 ,the ,inscriptions at ,copan2 ,carnegie ,inst4 of ,wash41 ,no4 #bai1 #aibj4 ,ellsworth ,huntington3 ,the ,red ,man's ,continent1 #aiai4 ,footnote #cg3 ,see summary of ,wolf's work with additional information by ,h4 ,fritz2 ,zuerich ,vierteljahrschrift1 ,vol4 #ch1 #ahic1 pp4 #gg-ajg4 ,,chapter ,,vii ,,glaciation ,,according ,,to ,,the ,,solar-,,cyclonic ,,hypothesis#ch ,the remarkable phenomena of glacial periods afford perhaps the best available test to which any climatic hypothesis can be subjected4 ,in this chapter and the two that follow1 we shall apply this test4 ,since much more is known about the recent ,great ,ice ,age1 or ,pleistocene glaciation1 than about the more ancient glaciations1 the problems of the ,pleistocene will receive especial attention4 ,in the present chapter the oncoming of glaciation and the subsequent disappearance of the ice will be outlined in the light of what would be expected according to the solar-cyclonic hypothesis4 ,then in the next chapter several problems of especial climatic significance will be considered1 such as the localization of ice sheets1 the succession of severe glacial and mild inter-glacial epochs1 the sudden commencement of glaciation and the peculiar variations in the height of the snow line4 ,other topics to be considered are the occurrence of pluvial or rainy climates in non-glaciated regions1 and glaciation near sea level in subtropical latitudes during the ,permian and ,proterozoic4 ,then in ,chapter ,,ix we shall consider the development and distribution of the remarkable deposits of wind-blown material known as loess4 ,facts not considered at the time of framing an hypothesis are especially significant in testing it4 ,in this particular case1 the cyclonic hypothesis was framed to explain the historic changes of climate revealed by a study of ruins1 tree rings1 and the terraces of streams and lakes1 without special thought of glaciation or other geologic changes4 ,indeed1 the hypothesis had reached nearly its present form before much attention was given to geological phases of the problem4 ,nevertheless1 it appears to meet even this severe test4 ,according to the solar-cyclonic hypothesis1 the ,pleistocene glacial period was inaugurated at a time when certain terrestrial conditions tended to make the earth especially favorable for glaciation4 ,how these conditions arose will be considered later4 ,here it is enough to state what they were4 ,chief among them was the fact that the continents stood unusually high and were unusually large4 ,this1 however1 was not the primary cause of glaciation1 for many of the areas which were soon to be glaciated were little above sea level4 ,for example1 it seems clear that ,new ,england stood less than a thousand feet higher than now4 ,indeed1 ,salisbury#ci estimates that eastern ,north ,america in general stood not more than a few hundred feet higher than now1 and ,w4 ,b4 ,wright#dj reaches the same conclusion in respect to the ,british ,isles4 ,nevertheless1 widespread lands1 even if they are not all high1 lead to climatic conditions which favor glaciation4 ,for example1 enlarged continents cause low temperature in high latitudes because they interfere with the ocean currents that carry heat polewards4 ,such continents also cause relatively cold winters1 for lands cool much sooner than does the ocean4 ,another result is a diminution of water vapor1 not only because cold air cannot hold much vapor1 but also because the oceanic area from which evaporation takes place is reduced by the emergence of the continents4 ,again1 when the continents are extensive the amount of carbonic acid gas in the atmosphere probably decreases1 for the augmented erosion due to uplift exposes much igneous rock to the air1 and weathering consumes the atmospheric carbon dioxide4 ,when the supply of water vapor and of atmospheric carbon dioxide is small1 an extreme type of climate usually prevails4 ,the combined result of all these conditions is that continental emergence causes the climate to be somewhat cool and to be marked by relatively great contrasts from season to season and from latitude to latitude4 ,when the terrestrial conditions thus permitted glaciation1 unusual solar activity is supposed to have greatly increased the number and severity of storms and to have altered their location1 just as now happens at times of many sunspots4 ,if such a change in storminess had occurred when terrestrial conditions were unfavorable for glaciation1 as1 for example1 when the lands were low and there were widespread epicontinental seas in middle and high latitudes1 glaciation might not have resulted4 ,in the ,pleistocene1 however1 terrestrial conditions permitted glaciation1 and therefore the supposed increase in storminess caused great ice sheets4 ,the conditions which prevail at times of increased storminess have been discussed in detail in ,earth and ,sun4 ,those which apparently brought on glaciation seem to have acted as follows3 ,in the first place the storminess lowered the temperature of the earth's surface in several ways4 ,the most important of these was the rapid upward convection in the centers of cyclonic storms whereby abundant heat was carried to high levels where most of it was radiated away into space4 ,the marked increase in the number of tropical cyclones which accompanies increased solar activity was probably important in this respect4 ,such cyclones carry vast quantities of heat and moisture out of the tropics4 ,the moisture1 to be sure1 liberates heat upon condensing1 but as condensation occurs above the earth's surface1 much of the heat escapes into space4 ,another reason for low temperature was that under the influence of the supposedly numerous storms of ,pleistocene times evaporation over the oceans must have increased4 ,this is largely because the velocity of the winds is relatively great when storms are strong and such winds are powerful agents of evaporation4 ,but evaporation requires heat1 and hence the strong winds lower the temperature4,b ,the second great condition which enabled increased storminess to bring on glaciation was the location of the storm tracks4 ,kullmer's maps1 as illustrated in ,fig4 #b1 suggest that a great increase in solar activity1 such as is postulated in the ,pleistocene1 might shift the main storm track poleward even more than it is shifted by the milder solar changes during the twelve-year sunspot cycle4 ,if this is so1 the main track would tend to cross ,north ,america through the middle of ,canada instead of near the southern border4 ,thus there would be an increase in precipitation in about the latitude of the ,keewatin and ,labradorean centers of glaciation4 ,from what is known of storm tracks in ,europe1 the main increase in the intensity of storms would probably center in ,scandinavia4 ,fig4 #c in ,chapter ,v bears this out4 ,that figure1 it will be recalled1 shows what happens to precipitation when solar activity is increasing4 ,a high rate of precipitation is especially marked in the boreal storm track1 that is1 in the northern ,united ,states1 southern ,canada1 and northwestern ,europe4 ,another important condition in bringing on glaciation would be the fact that when storms are numerous the total precipitation appears to increase in spite of the slightly lower temperature4 ,this is largely because of the greater evaporation4 ,the excessive evaporation arises partly from the rapidity of the winds1 as already stated1 and partly from the fact that in areas where the air is clear the sun would presumably be able to act more effectively than now4 ,it would do so because at times of abundant sunspots the sun in our own day has a higher solar constant than at times of milder activity4 ,our whole hypothesis is based on the supposition that what now happens at times of many sunspots was intensified in glacial periods4 ,a fourth condition which would cause glaciation to result from great solar activity would be the fact that the portion of the yearly precipitation falling as snow would increase1 while the proportion of rain would diminish in the main storm track4 ,this would arise partly because the storms would be located farther north than now1 and partly because of the diminution in temperature due to the increased convection4 ,the snow in itself would still further lower the temperature1 for snow is an excellent reflector of sunlight4 ,the increased cloudiness which would accompany the more abundant storms would also cause an unusually great reflection of the sunlight and still further lower the temperature4 ,thus at times of many sunspots a strong tendency toward the accumulation of snow would arise from the rapid convection and consequent low temperature1 from the northern location of storms1 from the increased evaporation and precipitation1 from the larger percentage of snowy rather than rainy precipitation1 and from the great loss of heat due to reflection from clouds and snow4 ,if events at the beginning of the last glacial period took place in accordance with the cyclonic hypothesis1 as outlined above1 one of the inevitable results would be the production of snowfields4 ,the places where snow would accumulate in special quantities would be central ,canada1 the ,labrador plateau1 and ,scandinavia1 as well as certain mountain regions4 ,as soon as a snowfield became somewhat extensive1 it would begin to produce striking climatic alterations in addition to those to which it owed its origin4#da ,for example1 within a snowfield the summers remain relatively cold4 ,hence such a field is likely to be an area of high pressure at all seasons4 ,the fact that the snowfield is always a place of relatively high pressure results in outblowing surface winds except when these are temporarily overcome by the passage of strong cyclonic storms4 ,the storms1 however1 tend to be concentrated near the margins of the ice throughout the year instead of following different paths in each of the four seasons4 ,this is partly because cyclonic lows always avoid places of high pressure and are thus pushed out of the areas where permanent snow has accumulated4 ,on the other hand1 at times of many sunspots1 as ,kullmer has shown1 the main storm track tends to be drawn poleward1 perhaps by electrical conditions4 ,hence when a snowfield is present in the north1 the lows1 instead of migrating much farther north in summer than in winter1 as they now do1 would merely crowd on to the snowfield a little farther in summer than in winter4 ,thus the heavy precipitation which is usual in humid climates near the centers of lows would take place near the advancing margin of the snowfield and cause the field to expand still farther southward4 ,the tendency toward the accumulation of snow on the margins of the snowfields would be intensified not only by the actual storms themselves1 but by other conditions4 ,for example1 the coldness of the snow would tend to cause prompt condensation of the moisture brought by the winds that blow toward the storm centers from low latitudes4 ,again1 in spite of the general dryness of the air over a snowfield1 the lower air contains some moisture due to evaporation from the snow by day during the clear sunny weather of anti-cyclones or highs4 ,where this is sufficient1 the cold surface of the snowfields tends to produce a frozen fog whenever the snowfield is cooled by radiation1 as happens at night and during the passage of highs4 ,such a frozen fog is an effective reflector of solar radiation4 ,moreover1 because ice has only half the specific heat of water1 and is much more transparent to heat1 such a radiation fog composed of ice crystals is a much less effective retainer of heat than clouds or fog made of unfrozen water particles4 ,shallow fogs of this type are described by several polar expeditions4 ,they clearly retard the melting of the snow and thus help the icefield to grow4 ,for all these reasons1 so long as storminess remained great1 the ,pleistocene snowfields1 according to the solar hypothesis1 must have deepened and expanded4 ,in due time some of the snow was converted into glacial ice4 ,when that occurred1 the growth of the snowfield as well as of the ice cap must have been accelerated by glacial movement4 ,under such circumstances1 as the ice crowded southward toward the source of the moisture by which it grew1 the area of high pressure produced by its low temperature would expand4 ,this would force the storm track southward in spite of the contrary tendency due to the sun4 ,when the ice sheet had become very extensive1 the track would be crowded relatively near to the northern margin of the trade-wind belt4 ,indeed1 the ,pleistocene ice sheets1 at the time of their maximum extension1 reached almost as far south as the latitude now marking the northern limit of the trade-wind belt in summer4 ,as the storm track with its frequent low pressure and the subtropical belt with its high pressure were forced nearer and nearer together1 the barometric gradient between the two presumably became greater1 winds became stronger1 and the storms more intense4 ,this zonal crowding would be of special importance in summer1 at which time it would also be most pronounced4 ,in the first place1 the storms would be crowded far upon the ice cap which would then be protected from the sun by a cover of fog and cloud more fully than at any other season4 ,furthermore1 the close approach of the trade-wind belt to the storm belt would result in a great increase in the amount of moisture drawn from the belt of evaporation which the trade winds dominate4 ,in the trade-wind belt1 clear skies and high temperature make evaporation especially rapid4 ,indeed1 in spite of the vast deserts it is probable that more than three-fourths of the total evaporation now taking place on the earth occurs in the belt of trades1 an area which includes about one-half of the earth's surface4 ,the agency which could produce this increased drawing northward of moisture from the trade-wind belt would be the winds blowing into the lows4 ,according to the cyclonic hypothesis1 many of these lows would be so strong that they would temporarily break down the subtropical belt of high pressure which now usually prevails between the trades and the zone of westerly winds4 ,this belt is even now often broken by tropical cyclones4 ,if the storms of more northerly regions temporarily destroyed the subtropical high-pressure belt1 even though they still remained on its northern side1 they would divert part of the trade winds4 ,hence the air which now is carried obliquely equatorward by those winds would be carried spirally northward into the cyclonic lows4 ,precipitation in the storm track on the margin of the relatively cold ice sheet would thus be much increased1 for most winds from low latitudes carry abundant moisture4 ,such a diversion of moisture from low latitudes probably explains the deficiency of precipitation along the heat equator at times of solar activity1 as shown in ,fig4 #c4 ,taken as a whole1 the summer conditions1 according to the cyclonic hypothesis1 would be such that increased evaporation in low latitudes would cooeperate with increased storminess1 cloudiness1 and fog in higher latitudes to preserve and increase the accumulation of ice upon the borders of the ice sheet4 ,the greater the storminess1 the more this would be true and the more the ice sheet would be able to hold its own against melting in summer4 ,such a combination of precipitation and of protection from the sun is especially important if an ice sheet is to grow4 ,the meteorologist needs no geologic evidence that the storm track was shoved equatorward by the growth of the ice sheet1 for he observes a similar shifting whenever a winter's snow cap occupies part of the normal storm tract4 ,the geologist1 however1 may welcome geologic evidence that such an extreme shift of the storm track actually occurred during the ,pleistocene4 ,harmer1 in #aija1 first pointed out the evidence which was repeated with approval by ,wright of the ,ireland ,geological ,survey in #aiad4db ,according to these authorities1 numerous boulders of a distinctive chalk were deposited by ,pleistocene icebergs along the coast of ,ireland4 ,their distribution shows that at the time of maximum glaciation the strong winds along the south coast of ,ireland were from the northeast while today they are from the southwest4 ,such a reversal could apparently be produced only by a southward shift of the center of the main storm track from its present position in northern ,ireland1 ,scotland1 and ,norway to a position across northern ,france1 central ,germany1 and middle ,russia4 ,this would mean that while now the centers of the lows commonly move northeastward a short distance north of southern ,ireland1 they formerly moved eastward a short distance south of ,ireland4 ,it will be recalled that in the northern hemisphere the winds spiral into a low counter-clockwise and that they are strongest near the center4 ,when the centers pass not far north of a given point1 the strong winds therefore blow from the west or southwest1 while when the centers pass just south of that point1 the strong winds come from the east or northeast4 ,in addition to the consequences of the crowding of the storm track toward the trade-wind belt1 several other conditions presumably operated to favor the growth of the ice sheet4 ,for example1 the lowering of the sea level by the removal of water to form the snowfields and glaciers interfered with warm currents4 ,it also increased the rate of erosion1 for it was equivalent to an uplift of all the land4 ,one consequence of erosion and weathering was presumably a diminution of the carbon dioxide in the atmosphere1 for although the ice covered perhaps a tenth of the lands and interfered with carbonation to that extent1 the removal of large quantities of soil by accelerated erosion on the other nine-tenths perhaps more than counterbalanced the protective effect of the ice4 ,at the same time1 the general lowering of the temperature of the ocean as well as the lands increased the ocean's capacity for carbon dioxide and thus facilitated absorption4 ,at a temperature of #ej deg4,f4 water absorbs #cb per cent more carbon dioxide than at #fh deg44 ,the high waves produced by the severe storms must have had a similar effect on a small scale4 ,thus the percentage of carbon dioxide in the atmosphere was presumably diminished4 ,of less significance than these changes in the lands and the air1 but perhaps not negligible1 was the increased salinity of the ocean which accompanied the removal of water to form snow1 and the increase of the dissolved mineral load of the rejuvenated streams4 ,increased salinity slows up the deep-sea circulation1 as we shall see in a later chapter4 ,this increases the contrasts from zone to zone4 ,at times of great solar activity the agencies mentioned above would apparently cooeperate to cause an advance of ice sheets into lower latitudes4 ,the degree of solar activity would have much to do with the final extent of the ice sheets4 ,nevertheless1 certain terrestrial conditions would tend to set limits beyond which the ice would not greatly advance unless the storminess were extraordinarily severe4 ,the most obvious of these conditions is the location of oceans and of deserts or semi-arid regions4 ,the southwestward advance of the ,european ice sheet and the southeastward advance of the ,labradorean sheet in ,america were stopped by the ,atlantic4 ,the semi-aridity of the ,great ,plains1 produced by their position in the lee of the ,rocky ,mountains1 stopped the advance of the ,keewatin ice sheet toward the southwest4 ,the advance of the ,european ice sheet southeast seems to have been stopped for similar reasons4 ,the cessation of the advance would be brought about in such an area not alone by the light precipitation and abundant sunshine1 but by the dryness of the air1 and also by the power of dust to absorb the sun's heat4 ,much dust would presumably be drawn in from the dry regions by passing cyclonic storms and would be scattered over the ice4 ,the advance of the ice is also slowed up by a rugged topography1 as among the ,appalachians in northern ,pennsylvania4 ,such a topography besides opposing a physical obstruction to the movement of the ice provides bare south-facing slopes which the sun warms effectively4 ,such warm slopes are unfavorable to glacial advance4 ,the rugged topography was perhaps quite as effective as the altitude of the ,appalachians in causing the conspicuous northward dent in the glacial margin in ,pennsylvania4 ,where glaciers lie in mountain valleys the advance beyond a certain point is often interfered with by the deployment of the ice at the mouths of gorges4 ,evaporation and melting are more rapid where a glacier is broad and thin than where it is narrow and thick1 as in a gorge4 ,again1 where the topography or the location of oceans or dry areas causes the glacial lobes to be long and narrow1 the elongation of the lobe is apparently checked in several ways4 ,toward the end of the lobe1 melting and evaporation increase rapidly because the planetary westerly winds are more likely to overcome the glacial winds and sweep across a long1 narrow lobe than across a broad one4 ,as they cross the lobe1 they accelerate evaporation1 and probably lessen cloudiness1 with a consequent augmentation of melting4 ,moreover1 although lows rarely cross a broad ice sheet1 they do cross a narrow lobe4 ,for example1 ,nansen records that strong lows occasionally cross the narrow southern part of the ,greenland ice sheet4 ,the longer the lobe1 the more likely it is that lows will cross it1 instead of following its margin4 ,lows which cross a lobe do not yield so much snow to the tip as do those which follow the margin4 ,hence elongation is retarded and finally stopped even without a change in the earth's general climate4 ,because of these various reasons the advances of the ice during the several epochs of a glacial period might be approximately equal1 even if the durations of the periods of storminess and low temperature were different4 ,indeed1 they might be sub-equal1 even if the periods differed in intensity as well as length4 ,differences in the periods would apparently be manifested less in the extent of the ice than in the depth of glacial erosion and in the thickness of the terminal moraines1 outwash plains1 and other glacial or glacio-fluvial formations4 ,having completed the consideration of the conditions leading to the advance of the ice1 let us now consider the condition of ,north ,america at the time of maximum glaciation4#dc ,over an area of nearly four million square miles1 occupying practically all the northern half of the continent and part of the southern half1 as appears in ,fig4 #f1 the surface was a monotonous and almost level plain of ice covered with snow4 ,when viewed from a high altitude1 all parts except the margins must have presented a uniformly white and sparkling appearance4 ,along the margins1 however1 except to the north1 the whiteness was irregular1 for the view must have included not only fresh snow1 but moving clouds and dirty snow or ice4 ,along the borders where melting was in progress there was presumably more or less spottedness due to morainal material or glacial debris brought to the surface by ice shearage and wastage4 ,along the dry southwestern border it is also possible that there were numerous dark spots due to dust blown onto the ice by the wind4 ,illustration3 ,fig4 #f4 ,distribution of ,pleistocene ice sheets4 7,after ,schuchert47 ,the great white sheet with its ragged border was roughly circular in form1 with its center in central ,canada4 ,yet there were many departures from a perfectly circular form4 ,some were due to the oceans1 for1 except in northern ,alaska1 the ice extended into the ocean all the way from ,new ,jersey around by the north to ,washington4 ,on the south1 topographic conditions made the margin depart from a simple arc4 ,from ,new ,jersey to ,ohio it swung northward4 ,in the ,mississippi ,valley it reached far south2 indeed most of the broad wedge between the ,ohio and the ,missouri rivers was occupied by ice4 ,from latitude #cg deg4 near the junction of the ,missouri and the ,mississippi1 however1 the ice margin extended almost due north along the ,missouri to central ,north ,dakota4 ,it then stretched westward to the ,rockies4 ,farther west lowland glaciation was abundant as far south as western ,washington4 ,in the ,rockies1 the ,cascades1 and the ,sierra ,nevadas glaciation was common as far south as ,colorado and southern ,california1 respectively1 and snowfields were doubtless extensive enough to make these ranges ribbons of white4 ,between these lofty ranges lay a great unglaciated region1 but even in the ,great ,basin itself1 in spite of its present aridity1 certain ranges carried glaciers1 while great lakes expanded widely4 ,in this vast field of snow the glacial ice slowly crept outward1 possibly at an average speed of half a foot a day1 but varying from almost nothing in winter at the north1 to several feet a day in summer at the south4#dd ,the force which caused the movement was the presence of the ice piled up not far from the margins4 ,almost certainly1 however1 there was no great dome from the center in ,canada outward1 as some early writers assumed4 ,such a dome would require that the ice be many thousands of feet thick near its center4 ,this is impossible because of the fact that ice is more voluminous than water 7about #i per cent near the freezing point74 ,hence when subjected to sufficient pressure it changes to the liquid form4 ,as friction and internal heat tend to keep the bottom of a glacier warm1 even in cold regions1 the probabilities are that only under very special conditions was a continental ice sheet much thicker than about #bejj feet4 ,in ,antarctica1 where the temperature is much lower than was probably attained in the ,united ,states1 the ice sheet is nearly level1 several expeditions having traveled hundreds of miles with practically no change in altitude4 ,in ,shackleton's trip almost to the ,south ,pole1 he encountered a general rise of #cjjj feet in #abjj miles4 ,mountains1 however1 projected through the ice even near the pole and the geologists conclude that the ice is not very thick even at the world's coldest point1 the ,south ,pole4 ,along the margin of the ice there were two sorts of movement1 much more rapid than the slow creep of the ice4 ,one was produced by the outward drift of snow carried by the outblowing dry winds and the other and more important was due to the passage of cyclonic storms4 ,along the border of the ice sheet1 except at the north1 storm presumably closely followed storm4 ,their movement1 we judge1 was relatively slow until near the southern end of the ,mississippi lobe1 but when this point was passed they moved much more rapidly1 for then they could go toward instead of away from the far northern path which the sun prescribes when solar activity is great4 ,the storms brought much snow to the icefield1 perhaps sometimes in favored places as much as the hundred feet a year which is recorded for some winters in the ,sierras at present4 ,even the unglaciated intermontane ,great ,basin presumably received considerable precipitation1 perhaps twice as much as its present scanty supply4 ,the rainfall was enough to support many lakes1 one of which was ten times as large as ,great ,salt ,lake2 and grass was doubtless abundant upon many slopes which are now dry and barren4 ,the relatively heavy precipitation in the ,great ,basin was probably due primarily to the increased number of storms1 but may also have been much influenced by their slow eastward movement4 ,the lows presumably moved slowly in that general region not only because they were retarded and turned from their normal path by the cold ice to the east1 but because during the summer the area between the ,sierra snowfields on the west and the ,rocky ,mountain and ,mississippi ,valley snowfields on the east was relatively warm4 ,hence it was normally a place of low pressure and therefore of inblowing winds4 ,slow-moving lows are much more effective than fast-moving ones in drawing moisture northwestward from the ,gulf of ,mexico1 for they give the moisture more time to move spirally first northeast1 under the influence of the normal southwesterly winds1 then northwest and finally southwest as it approaches the storm center4 ,in the case of the present lows1 before much moisture-laden air can describe such a circuit1 first eastward and then westward1 the storm center has nearly always moved eastward across the ,rockies and even across the ,great ,plains4 ,a result of this is the regular decrease in precipitation northward1 northwestward1 and westward from the ,gulf of ,mexico4 ,along the part of the glacial margins where for more than #cjjj miles the ,north ,american ice entered the ,atlantic and the ,pacific oceans1 myriads of great blocks broke off and floated away as stately icebergs1 to scatter boulders far over the ocean floor and to melt in warmer climes4 ,where the margin lay upon the lands numerous streams issued from beneath the ice1 milk-white with rock flour1 and built up great outwash plains and valley trains of gravel and sand4 ,here and there1 just beyond the ice1 marginal lakes of strange shapes occupied valleys which had been dammed by the advancing ice4 ,in many of them the water level rose until it reached some low point in the divide and then overflowed1 forming rapids and waterfalls4 ,indeed1 many of the waterfalls of the eastern ,united ,states and ,canada were formed in just this way and not a few streams now occupy courses through ridges instead of parallel to them1 as in pre-glacial times4 ,in the zone to the south of the continental ice sheet1 the plant and animal life of boreal1 cool temperate1 and warm temperate regions commingled curiously4 ,heather and ,arctic willow crowded out elm and oak2 musk ox1 hairy mammoth1 and marmot contested with deer1 chipmunk1 and skunk for a chance to live4 ,near the ice on slopes exposed to the cold glacial gales1 the immigrant boreal species were dominant1 but not far away in more protected areas the species that had formerly lived there held their own4 ,in ,europe during the last two advances of the great ice sheet the caveman also struggled with fierce animals and a fiercer climate to maintain life in an area whose habitability had long been decreasing4 ,the next step in our history of glaciation is to outline the disappearance of the ice sheets4 ,when a decrease in solar activity produced a corresponding decrease in storminess1 several influences presumably combined to cause the disappearance of the ice4 ,most of their results are the reverse of those which brought on glaciation4 ,a few special aspects1 however1 some of which have been discussed in ,earth and ,sun1 ought to be brought to mind4 ,a diminution in storminess lessens upward convection1 wind velocity1 and evaporation1 and these changes1 if they occurred1 must have united to raise the temperature of the lower air by reducing the escape of heat4 ,again a decrease in the number and intensity of tropical cyclones presumably lessened the amount of moisture carried into mid-latitudes1 and thus diminished the precipitation4 ,the diminution of snowfall on the ice sheets when storminess diminished was probably highly important4 ,the amount of precipitation on the sheets was presumably lessened still further by changes in the storminess of middle latitudes4 ,when storminess diminishes1 the lows follow a less definite path1 as ,kullmer's maps show1 and on the average a more southerly path4 ,thus1 instead of all the lows contributing snow to the ice sheet1 a large fraction of the relatively few remaining lows would bring rain to areas south of the ice sheet4 ,as storminess decreased1 the trades and westerlies probably became steadier1 and thus carried to high latitudes more warm water than when often interrupted by storms4 ,steadier southwesterly winds must have produced a greater movement of atmospheric as well as oceanic heat to high latitudes4 ,the warming due to these two causes was probably the chief reason for the disappearance of the ,european ice sheet and of those on the ,pacific coast of ,north ,america4 ,the two greater ,american ice sheets1 however1 and the glaciers elsewhere in the lee of high mountain ranges1 probably disappeared chiefly because of lessened precipitation4 ,if there were no cyclonic storms to draw moisture northward from the ,gulf of ,mexico1 most of ,north ,america east of the ,rocky ,mountain barrier would be arid4 ,therefore a diminution of storminess would be particularly effective in causing the disappearance of ice sheets in these regions4 ,that evaporation was an especially important factor in causing the ice from the ,keewatin center to disappear1 is suggested by the relatively small amount of water-sorted material in its drift4 ,in ,south ,dakota1 for example1 less than #aj per cent of the drift is stratified4#de ,on the other hand1 ,salisbury estimates that perhaps a third of the ,labradorean drift in eastern ,wisconsin is crudely stratified1 about half of that in ,new ,jersey1 and more than half of the drift in western ,europe4 ,when the sun's activity began to diminish1 all these conditions1 as well as several others1 would cooeperate to cause the ice sheets to disappear4 ,step by step with their disappearance1 the amelioration of the climate would progress so long as the period of solar inactivity continued and storms were rare4 ,if the inactivity continued long enough1 it would result in a fairly mild climate in high latitudes1 though so long as the continents were emergent this mildness would not be of the extreme type4 ,the inauguration of another cycle of increased disturbance of the sun1 with a marked increase in storminess1 would inaugurate another glacial epoch4 ,thus a succession of glacial and inter-glacial epochs might continue so long as the sun was repeatedly disturbed4 ,,footnotes3 ,footnote #ch3 ,this chapter is an amplification and revision of the sketch of the glacial period contained in ,the ,solar ,hypothesis of ,climatic ,changes2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #be1 #aiad4 ,footnote #ci3 ,r4 ,d4 ,salisbury3 ,physical ,geography of the ,pleistocene1 in ,outlines of ,geologic ,history1 by ,willis1 ,salisbury1 and others1 #aiaj1 p4 #bfe4 ,footnote #dj3 ,the ,quaternary ,ice ,age1 #aiad1 p4 #cfd4 ,footnote ,b3 ,for fuller discussion of climatic controls see ,s4 ,s4 ,visher3 ,seventy ,laws of ,climate1 ,annals ,assoc4 ,am4 ,geographers1 #aibb4 ,footnote #da3 ,many of these alterations are implied or discussed in the following papers3 #a4 ,f4 ,w4 ,harmer3 ,influence of ,winds upon the ,climate of the ,pleistocene2 ,quart4 ,jour4 ,geol4 ,soc41 ,vol4 #eg1 #aija1 p4 #dje4 #b4 ,c4 ,e4 ,p4 ,brooks3 ,meteorological ,conditions of an ,ice ,sheet2 ,quart4 ,jour4 ,royal ,meteorol4 ,soc41 ,vol4 #dj1 #aiad1 pp4 #ec-gj1 and ,the ,evolution of ,climate in ,northwest ,europe2 op4 cit41 ,vol4 #dg1 #aiba1 pp4 #agc-aid4 #c4 ,w4 ,h4 ,hobbs3 ,the ,role of the ,glacial ,anticyclone in the ,air ,circulation of the ,globe2 ,proc4 ,am4 ,phil4 ,soc41 ,vol4 #ed1 #aiae1 pp4 #ahe-bbe4 ,footnote #db3 ,w4 ,b4 ,wright3 ,the ,quaternary ,ice ,age1 #aiad1 p4 #ajj4 ,footnote #dc3 ,the description of the distribution of the ice sheet is based on ,t4 ,c4 ,chamberlin's wall map of ,north ,america at the maximum of glaciation1 #aiac4 ,footnote #dd3 ,chamberlin and ,salisbury3 ,geology1 #aijf1 ,vol4 #c1 and ,w4 ,h4 ,hobbs3 ,characteristics of ,existing ,glaciers1 #aiaa4 ,footnote #de3 ,s4 ,s4 ,visher3 ,the ,geography of ,south ,dakota2 ,s4 ,d4 ,geol4 ,surv41 #aiah4 ,,chapter ,,viii ,,some ,,problems ,,of ,,glacial ,,periods ,having outlined in general terms the coming of the ice sheets and their disappearance1 we are now ready to discuss certain problems of compelling climatic interest4 ,the discussion will be grouped under five heads3 7,i7 the localization of glaciation2 7,,ii7 the sudden coming of glaciation2 7,,iii7 peculiar variations in the height of the snow line and of glaciation2 7,,iv7 lakes and other evidences of humidity in unglaciated regions during the glacial epochs2 7,v7 glaciation at sea level and in low latitudes in the ,permian and ,proterozoic eras4 ,the discussion of perhaps the most difficult of all climatic problems of glaciation1 that of the succession of cold glacial and mild inter-glacial epochs1 has been postponed to the next to the final chapter of this book4 ,it cannot be properly considered until we take up the history of solar disturbances4 ,i4 ,the first problem1 the localization of the ice sheets1 arises from the fact that in both the ,pleistocene and the ,permian periods glaciation was remarkably limited4 ,in neither period were all parts of high latitudes glaciated2 yet in both cases glaciation occurred in large regions in lower latitudes4 ,many explanations of this localization have been offered1 but most are entirely inadequate4 ,even hypotheses with something of proven worth1 such as those of variations in volcanic dust and in atmospheric carbon dioxide1 fail to account for localization4 ,the cyclonic form of the solar hypothesis1 however1 seems to afford a satisfactory explanation4 ,the distribution of the ice in the last glacial period is well known1 and is shown in ,fig4 #f4 ,four-fifths of the ice-covered area1 which was eight million square miles1 more or less1 was near the borders of the ,north ,atlantic in eastern ,north ,america and northwestern ,europe4 ,the ice spread out from two great centers in ,north ,america1 the ,labradorean east of ,hudson ,bay1 and the ,keewatin west of the bay4 ,there were also many glaciers in the western mountains1 especially in ,canada1 while subordinate centers occurred in ,newfoundland1 the ,adirondacks1 and the ,white ,mountains4 ,the main ice sheet at its maximum extension reached as far south as latitude #ci deg4 in ,kansas and ,kentucky1 and #cg deg4 in ,illinois4 ,huge boulders were transferred more than one thousand miles from their source in ,canada4 ,the northward extension was somewhat less4 ,indeed1 the northern margin of the continent was apparently relatively little glaciated and much of ,alaska unglaciated4 ,why should northern ,kentucky be glaciated when northern ,alaska was not8 ,in ,europe the chief center from which the continental glacier moved was the ,scandinavian highlands4 ,it pushed across the depression now occupied by the ,baltic to southern ,russia and across the ,north ,sea depression to ,england and ,belgium4 ,the ,alps formed a center of considerable importance1 and there were minor centers in ,scotland1 ,ireland1 the ,pyrenees1 ,apennines1 ,caucasus1 and ,urals4 ,in ,asia numerous ranges also contained large glaciers1 but practically all the glaciation was of the alpine type and very little of the vast northern lowland was covered with ice4 ,in the southern hemisphere glaciation at low latitudes was less striking than in the northern hemisphere4 ,most of the increase in the areas of ice was confined to mountains which today receive heavy precipitation and still contain small glaciers4 ,indeed1 except for relatively slight glaciation in the ,australian ,alps and in ,tasmania1 most of the ,pleistocene glaciation in the southern hemisphere was merely an extension of existing glaciers1 such as those of south ,chile1 ,new ,zealand1 and the ,andes4 ,nevertheless1 fairly extensive glaciation existed much nearer the equator than is now the case4 ,in considering the localization of ,pleistocene glaciation1 three main factors must be taken into account1 namely1 temperature1 topography1 and precipitation4 ,the absence of glaciation in large parts of the ,arctic regions of ,north ,america and of ,asia makes it certain that low temperature was not the controlling factor4 ,aside from ,antarctica1 the coldest place in the world is northeastern ,siberia4 ,there for seven months the average temperature is below #j deg4,c41 while the mean for the whole year is below -#aj deg4,c4 ,if the temperature during a glacial period averaged #f deg4,c4 lower than now1 as is commonly supposed1 this part of ,siberia would have had a temperature below freezing for at least nine months out of the twelve even if there were no snowfield to keep the summers cold4 ,yet even under such conditions no glaciation occurred1 although in other places1 such as parts of ,canada and northwestern ,europe1 intense glaciation occurred where the mean temperature is much higher4 ,the topography of the lands apparently had much more influence upon the localization of glaciation than did temperature4 ,its effect1 however1 was always to cause glaciation exactly where it would be expected and not in unexpected places as actually occurred4 ,for example1 in ,north ,america the western side of the ,canadian ,rockies suffered intense glaciation1 for there precipitation was heavy because the westerly winds from the ,pacific are forced to give up their moisture as they rise4 ,in the same way the western side of the ,sierra ,nevadas was much more heavily glaciated than the eastern side4 ,in similar fashion the windward slopes of the ,alps1 the ,caucasus1 the ,himalayas1 and many other mountain ranges suffered extensive glaciation4 ,low temperature does not seem to have been the cause of this glaciation1 for in that case it is hard to see why both sides of the various ranges did not show an equal percentage of increase in the size of their icefields4 ,from what has been said as to temperature and topography1 it is evident that variations in precipitation have had much more to do with glaciation than have variations in temperature4 ,in the ,arctic lowlands and on the leeward side of mountains1 the slight development of glaciation appears to have been due to scarcity of precipitation4 ,on the windward side of mountains1 on the other hand1 a notable increase in precipitation seems to have led to abundant glaciation4 ,such an increase in precipitation must be dependent on increased evaporation and this could arise either from relatively high temperature or strong winds4 ,since the temperature in the glacial period was lower than now1 we seem forced to attribute the increased precipitation to a strengthening of the winds4 ,if the westerly winds from the ,pacific should increase in strength and waft more moisture to the western side of the ,canadian ,rockies1 or if similar winds increased the snowfall on the upper slopes of the ,alps or the ,tian-,shan ,mountains1 the glaciers would extend lower than now without any change in temperature4 ,although the incompetence of low temperature to cause glaciation1 and the relative unimportance of the mountains in northeastern ,canada and northwestern ,europe throw most glacial hypotheses out of court1 they are in harmony with the cyclonic hypothesis4 ,the answer of that hypothesis to the problem of the localization of ice sheets seems to be found in certain maps of storminess and rainfall in relation to solar activity4 ,in ,fig4 #b a marked belt of increased storminess at times of many sunspots is seen in southern ,canada4 ,a comparison of this with a series of maps given in ,earth and ,sun shows that the stormy belt tends to migrate northward in harmony with an increase in the activity of the sun's atmosphere4 ,if the sun were sufficiently active the belt of maximum storminess would apparently pass through the ,keewatin and ,labradorean centers of glaciation instead of well to the south of them1 as at present4 ,it would presumably cross another center in ,greenland1 and then would traverse the fourth of the great centers of ,pleistocene glaciation in ,scandinavia4 ,it would not succeed in traversing northern ,asia1 however1 any more than it does now1 because of the great high-pressure area which develops there in winter4 ,when the ice sheets expanded from the main centers of glaciation1 the belt of storms would be pushed southward and outward4 ,thus it might give rise to minor centers of glaciers such as the ,patrician between ,hudson ,bay and ,lake ,superior1 or the centers in ,ireland1 ,cornwall1 ,wales1 and the northern ,ural ,mountains4 ,as the main ice sheets advanced1 however1 the minor centers would be overridden and the entire mass of ice would be merged into one vast expanse in the ,atlantic portion of each of the two continents4 ,in this connection it may be well to consider briefly the most recent hypothesis as to the growth and hence the localization of glaciation4 ,in #aiaa and more fully in #aiae1 ,hobbs1#df advanced the anti-cyclonic hypothesis of the origin of ice sheets4 ,this hypothesis has the great merit of focusing attention upon the fact that ice sheets are pronounced anti-cyclonic regions of high pressure4 ,this is proved by the strong outblowing winds which prevail along their margins4 ,such winds must1 of course1 be balanced by inward-moving winds at high levels4 ,abundant observations prove that such is the case4 ,for example1 balloons sent up by ,barkow near the margin of the ,antarctic ice sheet reveal the occurrence of inblowing winds1 although they rarely occur below a height of #ijjj meters4 ,the abundant data gathered by ,guervain on the coast of ,greenland indicate that outblowing winds prevail up to a height of about #djjj meters4 ,at that height inblowing winds commence and increase in frequency until at an altitude of over #ejjj meters they become more common than outblowing winds4 ,it should be noted1 however1 that in both ,antarctica and ,greenland1 although the winds at an elevation of less than a thousand meters generally blow outward1 there are frequent and decided departures from this rule1 so that variable winds are quite commonly mentioned in the reports of expeditions and balloon soundings4 ,the undoubted anti-cyclonic conditions which ,hobbs thus calls to the attention of scientists seem to him to necessitate a peculiar mechanism in order to produce the snow which feeds the glaciers4 ,he assumes that the winds which blow toward the centers of the ice sheets at high levels carry the necessary moisture by which the glaciers grow4 ,when the air descends in the centers of the highs1 it is supposed to be chilled on reaching the surface of the ice1 and hence to give up its moisture in the form of minute crystals4 ,this conclusion is doubtful for several reasons4 ,in the first place1 ,hobbs does not seem to appreciate the importance of the variable winds which he quotes ,arctic and ,antarctic explorers as describing quite frequently on the edges of the ice sheets4 ,they are one of many signs that cyclonic storms are fairly frequent on the borders of the ice though not in its interior4 ,thus there is a distinct and sufficient form of precipitation actually at work near the margin of the ice1 or exactly where the thickness of the ice sheet would lead us to expect4 ,another consideration which throws grave doubt on the anti-cyclonic hypothesis of ice sheets is the small amount of moisture possible in the highs because of their low temperature4 ,suppose1 for the sake of argument1 that the temperature in the middle of an ice sheet averages #bj deg4,f4 ,this is probably much higher than the actual fact and therefore unduly favorable to the anti-cyclonic hypothesis4 ,suppose also that the decrease in temperature from the earth's surface upward proceeds at the rate of #a deg4,f4 for each #cjj feet1 which is #ej per cent less than the actual rate for air with only a slight amount of moisture1 such as is found in cold regions4 ,then at a height of #aj1jjj feet1 where the inblowing winds begin to be felt1 the temperature would be -#bj deg4,f4 ,at that temperature the air is able to hold approximately #j4aff grain of moisture per cubic foot when fully saturated4 ,this is an exceedingly small amount of moisture and even if it were all precipitated could scarcely build a glacier4 ,however1 it apparently would not be precipitated because when such air descends in the center of the anti-cyclone it is warmed adiabatically1 that is1 by compression4 ,on reaching the surface it would have a temperature of #bj deg4 and would be able to hold #j4hih grain of water vapor per cubic foot2 in other words1 it would have a relative humidity of about #ah per cent4 ,under no reasonable assumption does the upper air at the center of an ice sheet appear to reach the surface with a relative humidity of more than #bj or #be per cent4 ,such air cannot give up moisture4 ,on the contrary1 it absorbs it and tends to diminish rather than increase the thickness of the sheet of ice and snow4 ,but after the surplus heat gained by descent has been lost by radiation1 conduction1 and evaporation1 the air may become super-saturated with the moisture picked up while warm4 ,hobbs reports that explorers in ,antarctica and ,greenland have frequently observed condensation on their clothing4 ,if such moisture is not derived directly from the men's own bodies1 it is apparently picked up from the ice sheet by the descending air1 and not added to the ice sheet by air from aloft4 ,the relation of all this to the localization of ice sheets is this4 ,if ,hobbs' anti-cyclonic hypothesis of glacial growth is correct1 it would appear that ice sheets should grow up where the temperature is lowest and the high-pressure areas most persistent2 for instance1 in northern ,siberia4 ,it would also appear that so far as the topography permitted1 the ice sheets ought to move out uniformly in all directions2 hence the ice sheet ought to be as prominent to the north of the ,keewatin and ,labradorean centers as to the south1 which is by no means the case4 ,again1 in mountainous regions1 such as the glacial areas of ,alaska and ,chile1 the glaciation ought not to be confined to the windward slope of the mountains so closely as is actually the fact4 ,in each of these cases the glaciated region was large enough so that there was probably a true anti-cyclonic area comparable with that now prevailing over southern ,greenland4 ,in both places the correlation between glaciation and mountain ranges seems much too close to support the anti-cyclonic hypothesis1 for the inblowing winds which on that hypothesis bring the moisture are shown by observation to occur at heights far greater than that of all but the loftiest ranges4 ,,ii4 ,the sudden coming of glaciation is another problem which has been a stumbling-block in the way of every glacial hypothesis4 ,in his ,climates of ,geologic ,times1 ,schuchert states that the fossils give almost no warning of an approaching catastrophe4 ,if glaciation were solely due to uplift1 or other terrestrial changes aside from vulcanism1 ,schuchert holds that it would have come slowly and the stages preceding glaciation would have affected life sufficiently to be recorded in the rocks4 ,he considers that the suddenness of the coming of glaciation is one of the strongest arguments against the carbon dioxide hypothesis of glaciation4 ,according to the cyclonic hypothesis1 however1 the suddenness of the oncoming of glaciation is merely what would be expected on the basis of what happens today4 ,changes in the sun occur suddenly4 ,the sunspot cycle is only eleven or twelve years long1 and even this short period of activity is inaugurated more suddenly than it declines4 ,again the climatic record derived from the growth of trees1 as given in ,figs4 #d and #e1 also shows that marked changes in climate are initiated more rapidly than they disappear4 ,in this connection1 however1 it must be remembered that solar activity may arise in various ways1 as will appear more fully later4 ,under certain conditions storminess may increase and decrease slowly4 ,,iii4 ,the height of the snow line and of glaciation furnishes another means of testing glacial hypotheses4 ,it is well established that in times of glaciation the snow line was depressed everywhere1 but least near the equator4 ,for example1 according to ,penck1 permanent snow extended #djjj feet lower than now in the ,alps1 whereas it stood only #aejj feet below the present level near the equator in ,venezuela4 ,this unequal depression is not readily accounted for by any hypothesis depending solely upon the lowering of temperature4 ,by the carbon dioxide and the volcanic dust hypotheses1 the temperature presumably was lowered almost equally in all latitudes1 but a little more at the equator than elsewhere4 ,if glaciation were due to a temporary lessening of the radiation received from the sun1 such as is demanded by the thermal solar hypothesis1 and by the longer periods of ,croll's hypothesis1 the lowering would be distinctly greatest at the equator4 ,thus1 according to all these hypotheses1 the snow line should have been depressed most at the equator1 instead of least4 ,the cyclonic hypothesis explains the lesser depression of the snow line at the equator as due to a diminution of precipitation4 ,the effectiveness of precipitation in this respect is illustrated by the present great difference in the height of the snow line on the humid and dry sides of mountains4 ,on the wet eastern side of the ,andes near the equator1 the snow line lies at #af1jjj feet2 on the dry western side1 at #ah1ejj feet4 ,again1 although the humid side of the ,himalayas lies toward the south1 the snow line has a level of #ae1jjj feet1 while farther north1 on the dry side1 it is #af1gjj feet4#dg ,the fact that the snow line is lower near the margin of the ,alps than toward the center points in the same direction4 ,the bearing of all this on the glacial period may be judged by looking again at ,fig4 #c in ,chapter ,v4 ,this shows that at times of sunspot activity and hence of augmented storminess1 the precipitation diminishes near the heat equator1 that is1 where the average temperature for the whole year is highest4 ,at present the great size of the northern continents and their consequent high temperature in summer1 cause the heat equator to lie north of the real equator1 except where ,australia draws it to the southward4#dh ,when large parts of the northern continents were covered with ice1 however1 the heat equator and the true equator were probably much closer than now1 for the continents could not become so hot4 ,if so1 the diminution in equatorial precipitation1 which accompanies increased storminess throughout the world as a whole1 would take place more nearly along the true equator than appears in ,fig4 #c4 ,hence so far as precipitation alone is concerned1 we should actually expect that the snow line near the equator would rise a little during glacial periods4 ,another factor1 however1 must be considered4 ,koeppen's data1 it will be remembered1 show that at times of solar activity the earth's temperature falls more at the equator than in higher latitudes4 ,if this effect were magnified it would lower the snow line4 ,the actual position of the snow line at the equator during glacial periods thus appears to be the combined effect of diminished precipitation1 which would raise the line1 and of lower temperature1 which would bring it down4 ,before leaving this subject it may be well to recall that the relative lessening of precipitation in equatorial latitudes during the glacial epochs was probably caused by the diversion of moisture from the trade-wind belt4 ,this diversion was presumably due to the great number of tropical cyclones and to the fact that the cyclonic storms of middle latitudes also drew much moisture from the trade-wind belt in summer when the northern position of the sun drew that belt near the storm track which was forced to remain south of the ice sheet4 ,such diversion of moisture out of the trade-wind belt must diminish the amount of water vapor that is carried by the trades to equatorial regions2 hence it would lessen precipitation in the belt of so-called equatorial calms1 which lies along the heat equator rather than along the geographical equator4 ,another phase of the vertical distribution of glaciation has been the subject of considerable discussion4 ,in the ,alps and in many other mountains the glaciation of the ,pleistocene period appears to have had its upper limit no higher than today4 ,this has been variously interpreted4 ,it seems1 however1 to be adequately explained as due to decreased precipitation at high altitudes during the cold periods4 ,this is in spite of the fact that precipitation in general increased with increased storminess4 ,the low temperature of glacial times presumably induced condensation at lower altitudes than now1 and most of the precipitation occurred upon the lower slopes of the mountains1 contributing to the lower glaciers1 while little of it fell upon the highest glaciers4 ,above a moderate altitude in all lofty mountains the decrease in the amount of precipitation is rapid4 ,in most cases the decrease begins at a height of less than #cjjj feet above the base of the main slope1 provided the slope is steep4 ,the colder the air1 the lower the altitude at which this occurs4 ,for example1 it is much lower in winter than in summer4 ,indeed1 the higher altitudes in the ,alps are sunny in winter even where there are abundant clouds lower down4 ,,iv4 ,the presence of extensive lakes and other evidences of a pluvial climate during glacial periods in non-glaciated regions which are normally dry is another of the facts which most glacial hypotheses fail to explain satisfactorily4 ,beyond the ice sheets many regions appear to have enjoyed an unusually heavy precipitation during the glacial epochs4 ,the evidence of this is abundant1 including numerous abandoned strand lines of salt lakes and an abundance of coarse material in deltas and flood plains4 ,j4 ,d4 ,whitney1#di in an interesting but neglected volume1 was one of the first to marshal the evidence of this sort4 ,more recently ,free#ej has amplified this4 ,according to him in the ,great ,basin region of the ,united ,states sixty-two basins either contain unmistakable evidence of lakes1 or belong to one of the three great lake groups named below4 ,two of these1 the ,lake ,lahontan and the ,lake ,bonneville groups1 comprise twenty-nine present basins1 while the third1 the ,owens-,searles chain1 contained at least five large lakes1 the lowest being in ,death ,valley4 ,in western and central ,asia a far greater series of salt lakes is found and most of these are surrounded by strands at high levels4 ,many of these are described in ,explorations in ,turkestan1 ,the ,pulse of ,asia1 and ,palestine and ,its ,transformation4 ,there has been a good deal of debate as to whether these lakes actually date from the glacial period1 as is claimed by ,c4 ,e4 ,p4 ,brooks1 for example1 or from some other period4 ,the evidence1 however1 seems to be convincing that the lakes expanded when the ice also expanded4 ,according to the older glacial hypotheses the lower temperature which is postulated as the cause of glaciation would almost certainly mean less evaporation over the oceans and hence less precipitation during glacial periods4 ,to counteract this the only way in which the level of the lakes could be raised would be because the lower temperature would cause less evaporation from their surfaces4 ,it seems quite impossible1 however1 that the lowering of temperature1 which is commonly taken to have been not more than #aj deg4,c41 could counteract the lessened precipitation and also cause an enormous expansion of most of the lakes4 ,for example1 ancient ,lake ,bonneville was more than ten times as large as its modern remnant1 ,great ,salt ,lake1 and its average depth more than forty times as great4#ea ,many small lakes in the ,old ,world expanded still more4#eb ,for example1 in eastern ,persia many basins which now contain no lake whatever are floored with vast deposits of lacustrine salt and are surrounded by old lake bluffs and beaches4 ,in northern ,africa similar conditions prevail4#ec ,other1 but less obvious1 evidence of more abundant rainfall in regions that are now dry is found in thick strata of gravel1 sand1 and fine silt in the alluvial deposits of flood plains and deltas4#ed ,the cyclonic hypothesis supposes that increased storminess accounts for pluvial climates in regions that are now dry just as it accounts for glaciation in the regions of the ice sheets4 ,figs4 #b and #c1 it will be remembered1 illustrate what happens when the sun is active4 ,solar activity is accompanied by an increase in storminess in the southwestern ,united ,states in exactly the region where elevated strands of diminished salt lakes are most numerous4 ,in ,fig4 #c1 the same condition is seen in the region of salt lakes in the ,old ,world4 ,judging by these maps1 which illustrate what has happened since careful meteorological records were kept1 an increase in solar activity is accompanied by increased rainfall in large parts of what are now semi-arid and desert regions4 ,such precipitation would at once cause the level of the lakes to rise4 ,later1 when ice sheets had developed in ,europe and ,america1 the high-pressure areas thus caused might force the main storm belt so far south that it would lie over these same arid regions4 ,the increase in tropical hurricanes at times of abundant sunspots may also have a bearing on the climate of regions that are now arid4 ,during the glacial period some of the hurricanes probably swept far over the lands4 ,the numerous tropical cyclones of ,australia1 for example1 are the chief source of precipitation for that continent4#ee ,some of the stronger cyclones locally yield more rain in a day or two than other sources yield in a year4 ,v4 ,the occurrence of widespread glaciation near the tropics during the ,permian1 as shown in ,fig4 #g1 has given rise to much discussion4 ,the recent discovery of glaciation in latitudes as low as #cj deg4 in the ,proterozoic is correspondingly significant4 ,in all cases the occurrence of glaciation in low and middle latitudes is probably due to the same general causes4 ,doubtless the position and altitude of the mountains had something to do with the matter4 ,yet taken by itself this seems insufficient4 ,today the loftiest range in the world1 the ,himalayas1 is almost unglaciated1 although its southern slope may seem at first thought to be almost ideally located in this respect4 ,some parts rise over #bj1jjj feet and certain lower slopes receive #djj inches of rain per year4 ,the small size of the ,himalayan glaciers in spite of these favorable conditions is apparently due largely to the seasonal character of the monsoon winds4 ,the strong outblowing monsoons of winter cause about half the year to be very dry with clear skies and dry winds from the interior of ,asia4 ,in all low latitudes the sun rides high in the heavens at midday1 even in winter1 and thus melts snow fairly effectively in clear weather4 ,this is highly unfavorable to glaciation4 ,the inblowing southern monsoons bring all their moisture in midsummer at just the time when it is least effective in producing snow4 ,conditions similar to those now prevailing in the ,himalayas must accompany any great uplift of the lands which produces high mountains and large continents in subtropical and middle latitudes4 ,hence1 uplift alone cannot account for extensive glaciation in subtropical latitudes during the ,permian and ,proterozoic4 ,illustration3 ,fig4 #g4 ,permian geography and glaciation4 7,after ,schuchert47 ,the assumption of a great general lowering of temperature is also not adequate to explain glaciation in subtropical latitudes4 ,in the first place this would require a lowering of many degrees1--far more than in the ,pleistocene glacial period4 ,the marine fossils of the ,permian1 however1 do not indicate any such condition4 ,in the second place1 if the lands were widespread as they appear to have been in the ,permian1 a general lowering of temperature would diminish rather than increase the present slight efficiency of the monsoons in producing glaciation4 ,monsoons depend upon the difference between the temperatures of land and water4 ,if the general temperature were lowered1 the reduction would be much less pronounced on the oceans than on the lands1 for water tends to preserve a uniform temperature1 not only because of its mobility1 but because of the large amount of heat given out when freezing takes place1 or consumed in evaporation4 ,hence the general lowering of temperature would make the contrast between continents and oceans less than at present in summer1 for the land temperature would be brought toward that of the ocean4 ,this would diminish the strength of the inblowing summer monsoons and thus cut off part of the supply of moisture4 ,evidence that this actually happened in the cold fourteenth century has already been given in ,chapter ,,vi4 ,on the other hand1 in winter the lands would be much colder than now and the oceans only a little colder1 so that the dry outblowing monsoons of the cold season would increase in strength and would also last longer than at present4 ,in addition to all this1 the mere fact of low temperature would mean a general reduction in the amount of water vapor in the air4 ,thus1 from almost every point of view a mere lowering of temperature seems to be ruled out as a cause of ,permian glaciation4 ,moreover1 if the ,permian or ,proterozoic glacial periods were so cold that the lands above latitude #cj deg4 were snow-covered most of the time1 the normal surface winds in subtropical latitudes would be largely equatorward1 just as the winter monsoons now are4 ,hence little or no moisture would be available to feed the snowfields which give rise to the glaciers4 ,it has been assumed by ,marsden ,manson and others that increased general cloudiness would account for the subtropical glaciation of the ,permian and ,proterozoic4 ,granting for the moment that there could be universal persistent cloudiness1 this would not prevent or counteract the outblowing anti-cyclonic winds so characteristic of great snowfields4 ,therefore1 under the hypothesis of general cloudiness there would be no supply of moisture to cause glaciation in low latitudes4 ,indeed1 persistent cloudiness in all higher latitudes would apparently deprive the ,himalayas of most of their present moisture1 for the interior of ,asia would not become hot in summer and no inblowing monsoons would develop4 ,in fact1 winds of all kinds would seemingly be scarce1 for they arise almost wholly from contrasts of temperature and hence of atmospheric pressure4 ,the only way to get winds and hence precipitation would be to invoke some other agency1 such as cyclonic storms1 but that would be a departure from the supposition that glaciation arose from cloudiness4 ,let us now inquire how the cyclonic hypothesis accounts for glaciation in low latitudes4 ,we will first consider the terrestrial conditions in the early ,permian1 the last period of glaciation in such latitudes4 ,geologists are almost universally agreed that the lands were exceptionally extensive and also high1 especially in low latitudes4 ,one evidence of this is the presence of abundant conglomerates composed of great boulders4 ,it is also probable that the carbon dioxide in the air during the early ,permian had been reduced to a minimum by the extraordinary amount of coal formed during the preceding period4 ,this would tend to produce low temperature and thus make the conditions favorable for glaciation as soon as an accentuation of solar activity caused unusual storminess4 ,if the storminess became extreme when terrestrial conditions were thus universally favorable to glaciation1 it would presumably produce glaciation in low latitudes4 ,numerous and intense tropical cyclones would carry a vast amount of moisture out of the tropics1 just as now happens when the sun is active1 but on a far larger scale4 ,the moisture would be precipitated on the equatorward slopes of the subtropical mountain ranges4 ,at high elevations this precipitation would be in the form of snow even in summer4 ,tropical cyclones1 however1 as is shown in ,earth and ,sun1 occur in the autumn and winter as well as in summer4 ,for example1 in the ,bay of ,bengal the number recorded in ,october is fifty1 the largest for any month2 while in ,november it is thirty-four1 and ,december fourteen as compared with an average of forty-two for the months of ,july to ,september4 ,from ,january to ,march1 when sunspot numbers averaged more than forty1 the number of tropical hurricanes was #adc per cent greater than when the sunspot numbers averaged below forty4 ,during the months from ,april to ,june1 which also would be times of considerable snowy precipitation1 tropical hurricanes averaged #eh per cent more numerous with sunspot numbers above forty than with numbers below forty1 while from ,july to ,september the difference amounted to #bc per cent4 ,even at this season some snow falls on the higher slopes1 while the increased cloudiness due to numerous storms also tends to preserve the snow4 ,thus a great increase in the frequency of sunspots is accompanied by increased intensity of tropical hurricanes1 especially in the cooler autumn and spring months1 and results not only in a greater accumulation of snow but in a decrease in the melting of the snow because of more abundant clouds4 ,at such times as the ,permian1 the general low temperature due to rapid convection and to the scarcity of carbon dioxide presumably joined with the extension of the lands in producing great high-pressure areas over the lands in middle latitudes during the winters1 and thus caused the more northern1 or mid-latitude type of cyclonic storms to be shifted to the equatorward side of the continents at that season4 ,this would cause an increase of precipitation in winter as well as during the months when tropical hurricanes abound4 ,many other circumstances would cooeperate to produce a similar result4 ,for example1 the general low temperature would cause the sea to be covered with ice in lower latitudes than now1 and would help to create high-pressure areas in middle latitudes1 thus driving the storms far south4 ,if the sea water were fresher than now1 as it probably was to a notable extent in the ,proterozoic and perhaps to some slight extent in the ,permian1 the higher freezing point would also further the extension of the ice and help to keep the storms away from high latitudes4 ,if to this there is added a distribution of land and sea such that the volume of the warm ocean currents flowing from low to high latitudes was diminished1 as appears to have been the case1 there seems to be no difficulty in explaining the subtropical location of the main glaciation in both the ,permian and the ,proterozoic4 ,an increase of storminess seems to be the key to the whole situation4 ,one other possibility may be mentioned1 although little stress should be laid on it4 ,in ,earth and ,sun it has been shown that the main storm track in both the northern and southern hemispheres is not concentric with the geographical poles4 ,both tracks are roughly concentric with the corresponding magnetic poles1 a fact which may be important in connection with the hypothesis of an electrical effect of the sun upon terrestrial storminess4 ,the magnetic poles are known to wander considerably4 ,such wandering gives rise to variations in the direction of the magnetic needle from year to year4 ,in #ahae the compass in ,england pointed #bd-a_/b deg4 ,w4 of ,n4 and in #aijf #ag deg4 #de' ,w4 ,such a variation seems to mean a change of many miles in the location of the north magnetic pole4 ,certain changes in the daily march of electromagnetic phenomena over the oceans have led ,bauer and his associates to suggest that the magnetic poles may even be subject to a slight daily movement in response to the changes in the relative positions of the earth and sun4 ,thus there seems to be a possibility that a pronounced change in the location of the magnetic pole in ,permian times1 for example1 may have had some connection with a shifting in the location of the belt of storms4 ,it must be clearly understood that there is as yet no evidence of any such change1 and the matter is introduced merely to call attention to a possible line of investigation4 ,any hypothesis of ,permian and ,proterozoic glaciation must explain not only the glaciation of low latitudes but the lack of glaciation and the accumulation of red desert beds in high latitudes4 ,the facts already presented seem to explain this4 ,glaciation could not occur extensively in high latitudes partly because during most of the year the air was too cold to hold much moisture1 but still more because the winds for the most part must have blown outward from the cold northern areas and the cyclonic storm belt was pushed out of high latitudes4 ,because of these conditions precipitation was apparently limited to a relatively small number of storms during the summer4 ,hence great desert areas must have prevailed at high latitudes4 ,great aridity now prevails north of the ,himalayas and related ranges1 and red beds are accumulating in the centers of the great deserts1 such as those of the ,tarim ,basin and the ,transcaspian4 ,the redness is not due to the original character of the rock1 but to intense oxidation1 as appears from the fact that along the edges of the desert and wherever occasional floods carry sediment far out into the midst of the sand1 the material has the ordinary brownish shades4 ,as soon as one goes out into the places where the sand has been exposed to the air for a long time1 however1 it becomes pink1 and then red4 ,such conditions may have given rise to the high degree of oxidation in the famous ,permian red beds4 ,if the air of the early ,permian contained an unusual percentage of oxygen because of the release of that gas by the great plant beds which formed coal in the preceding era1 as ,chamberlin has thought probable1 the tendency to produce red beds would be still further increased4 ,it must not be supposed1 however1 that these conditions would absolutely limit glaciation to subtropical latitudes4 ,the presence of early ,permian glaciation in ,north ,america at ,boston and in ,alaska and in the ,falkland ,islands of the ,south ,atlantic ,ocean proves that at least locally there was sufficient moisture to form glaciers near the coast in relatively high latitudes4 ,the possibility of this would depend entirely upon the form of the lands and the consequent course of ocean currents4 ,even in those high latitudes cyclonic storms would occur unless they were kept out by conditions of pressure such as have been described above4 ,the marine faunas of ,permian age in high latitudes have been interpreted as indicating mild oceanic temperatures4 ,this is a point which requires further investigation4 ,warm oceans during times of slight solar activity are a necessary consequence of the cyclonic hypothesis1 as will appear later4 ,the present cold oceans seem to be the expectable result of the ,pleistocene glaciation and of the present relatively disturbed condition of the sun4 ,if a sudden disturbance threw the solar atmosphere into violent commotion within a few thousand years during ,permian times1 glaciation might occur as described above1 while the oceans were still warm4 ,in fact their warmth would increase evaporation while the violent cyclonic storms and high winds would cause heavy rain and keep the air cool by constantly raising it to high levels where it would rapidly radiate its heat into space4 ,nevertheless it is not yet possible to determine how warm the oceans were at the actual time of the ,permian glaciation4 ,some faunas formerly reported as ,permian are now known to be considerably older4 ,moreover1 others of undoubted ,permian age are probably not strictly contemporaneous with the glaciation4 ,so far back in the geological record it is very doubtful whether we can date fossils within the limits of say #ajj1jjj years4 ,yet a difference of #ajj1jjj years would be more than enough to allow the fossils to have lived either before or after the glaciation1 or in an inter-glacial epoch4 ,one such epoch is known to have occurred and nine others are suggested by the inter-stratification of glacial till and marine sediments in eastern ,australia4 ,the warm currents which would flow poleward in inter-glacial epochs must have favored a prompt reintroduction of marine faunas driven out during times of glaciation4 ,taken all and all1 the ,permian glaciation seems to be accounted for by the cyclonic hypothesis quite as well as does the ,pleistocene4 ,in both these cases1 as well as in the various pulsations of historic times1 it seems to be necessary merely to magnify what is happening today in order to reproduce the conditions which prevailed in the past4 ,if the conditions which now prevail at times of sunspot minima were magnified1 they would give the mild conditions of inter-glacial epochs and similar periods4 ,if the conditions which now prevail at times of sunspot maxima are magnified a little they seem to produce periods of climatic stress such as those of the fourteenth century4 ,if they are magnified still more the result is apparently glacial epochs like those of the ,pleistocene1 and if they are magnified to a still greater extent1 the result is ,permian or ,proterozoic glaciation4 ,other factors must indeed be favorable1 for climatic changes are highly complex and are unquestionably due to a combination of circumstances4 ,the point which is chiefly emphasized in this book is that among those several circumstances1 changes in cyclonic storms due apparently to activity of the sun's atmosphere must always be reckoned4 ,,footnotes3 ,footnote #df3 ,w4 ,h4 ,hobbs3 ,characteristics of ,existing ,glaciers1 #aiaa4 ,the ,role of the ,glacial ,anticyclones in the ,air ,circulation of the ,globe2 ,proc4 ,am4 ,phil4 ,soc41 ,vol4 #ed1 #aiae1 pp4 #ahe-bbe4 ,footnote #dg3 ,r4 ,d4 ,salisbury3 ,physiography1 #aiai4 ,footnote #dh3 ,griffith ,taylor3 ,australian ,meteorology1 #aibj1 p4 #bhc4 ,footnote #di3 ,j4 ,d4 ,whitney3 ,climatic ,changes of the ,later ,geological ,times1 #ahhb4 ,footnote #ej3 ,e4 ,e4 ,free3 ,u4 ,s4 ,dept4 of ,agriculture1 ,bull4 #ed1 #aiad4 ,mr4 ,free has prepared a summary of this ,bulletin which appears in ,the ,solar ,hypothesis1 ,bull4 ,geol4 ,sec4 of ,am41 ,vol4 #be1 pp4 #eei-efb4 ,footnote #ea3 ,g4 ,k4 ,gilbert3 ,lake ,bonneville2 ,monograph #a1 ,u4 ,s4 ,geol4 ,surv4 ,footnote #eb3 ,c4 ,e4 ,p4 ,brooks3 ,quart4 ,jour4 ,royal ,meteorol4 ,soc41 #aiad1 pp4 #fc-ff4 ,footnote #ec3 ,h4 ,j4 ,l4 ,beadnell3 ,a4 ,egyptian ,oasis1 ,london1 #aiji4 ,ellsworth ,huntington3 ,the ,libyan ,oasis of ,kharga2 ,bull4 ,am4 ,geog4 ,soc41 ,vol4 #db1 ,sept41 #aiaj1 pp4 #fda-ffa4 ,footnote #ed3 ,s4 ,s4 ,visher3 ,the ,bajada of the ,tucson ,bolson of ,southern ,arizona2 ,science1 ,n4 ,s41 ,mar4 #bc1 #aiac4 ,ellsworth ,huntington3 ,the ,basins of ,eastern ,persia and ,seistan1 in ,explorations in ,turkestan4 ,footnote #ee3 ,griffith ,taylor3 ,australian ,meteorology1 #aibj1 p4 #ahi4 ,,chapter ,,ix ,,the ,,origin ,,of ,,loess ,one of the most remarkable formations associated with glacial deposits consists of vast sheets of the fine-grained1 yellowish1 wind-blown material called loess4 ,somewhat peculiar climatic conditions evidently prevailed when it was formed4 ,at present similar deposits are being laid down only near the leeward margin of great deserts4 ,the famous loess deposits of ,china in the lee of the ,desert of ,gobi are examples4 ,during the ,pleistocene period1 however1 loess accumulated in a broad zone along the margin of the ice sheet at its maximum extent4 ,in the ,old ,world it extended from ,france across ,germany and through the ,black ,earth region of ,russia into ,siberia4 ,in the ,new ,world a still larger area is loess-covered4 ,in the ,mississippi ,valley1 tens of thousands of square miles are mantled by a layer exceeding twenty feet in thickness and in many places approaching a hundred feet4 ,neither the ,north ,american nor the ,european deposits are associated with a desert4 ,indeed1 loess is lacking in the western and drier parts of the great plains and is best developed in the well-watered states of ,iowa1 ,illinois1 and ,missouri4 ,part of the loess overlies the non-glacial materials of the great central plain1 but the northern portions overlie the drift deposits of the first three glaciations4 ,a few traces of loess are associated with the ,kansan and ,illinoian1 the second and third glaciations1 but most of the ,america loess appears to have been formed at approximately the time of the ,iowan or fourth glaciation1 while only a little overlies the drift sheets of the ,wisconsin age4 ,the loess is thickest near the margin of the ,iowan till sheet and thins progressively both north and south4 ,the thinning southward is abrupt along the stream divides1 but very gradual along the larger valleys4 ,indeed1 loess is abundant along the bluffs of the ,mississippi1 especially the east bluff1 almost to the ,gulf of ,mexico4#ef ,it is now generally agreed that all typical loess is wind blown4 ,there is still much question1 however1 as to its time of origin1 and thus indirectly as to its climatic implications4 ,several ,american and ,european students have thought that the loess dates from inter-glacial times4 ,on the other hand1 ,penck has concluded that the loess was formed shortly before the commencement of the glacial epochs2 while many ,american geologists hold that the loess accumulated while the ice sheets were at approximately their maximum size4 ,w4 ,j4 ,mc,gee1 ,chamberlin and ,salisbury1 ,keyes1 and others lean toward this view4 ,in this chapter the hypothesis is advanced that it was formed at the one other possible time1 namely1 immediately following the retreat of the ice4 ,these four hypotheses as to the time of origin of loess imply the following differences in its climatic relations4 ,if loess was formed during typical inter-glacial epochs1 or toward the close of such epochs1 profound general aridity must seemingly have prevailed in order to kill off the vegetation and thus enable the wind to pick up sufficient dust4 ,if the loess was formed during times of extreme glaciation when the glaciers were supplying large quantities of fine material to outflowing streams1 less aridity would be required1 but there must have been sharp contrasts between wet seasons in summer when the snow was melting and dry seasons in winter when the storms were forced far south by the glacial high pressure4 ,alternate floods and droughts would thus affect broad areas along the streams4 ,hence arises the hypothesis that the wind obtained the loess from the flood plains of streams at times of maximum glaciation4 ,if the loess was formed during the rapid retreat of the ice1 alternate summer floods and winter droughts would still prevail1 but much material could also be obtained by the winds not only from flood plains1 but also from the deposits exposed by the melting of the ice and not yet covered by vegetation4 ,the evidence for and against the several hypotheses may be stated briefly4 ,in support of the hypothesis of the inter-glacial origin of loess1 ,shimek and others state that the glacial drift which lies beneath the loess commonly gives evidence that some time elapsed between the disappearance of the ice and the deposition of the loess4 ,for example1 abundant shells of land snails in the loess are not of the sort now found in colder regions1 but resemble those found in the drier regions4 ,it is probable that if they represented a glacial epoch they would be depauperated by the cold as are the snails of far northern regions4 ,the gravel pavement discussed below seems to be strong evidence of erosion between the retreat of the ice and the deposition of the loess4 ,turning to the second hypothesis1 namely1 that the loess accumulated near the close of the inter-glacial epoch rather than in the midst of it1 we may follow ,penck4 ,the mammalian fossils seem to him to prove that the loess was formed while boreal animals occupied the region1 for they include remains of the hairy mammoth1 woolly rhinoceros1 and reindeer4 ,on the other hand1 the typical inter-glacial beds not far away yield remains of species characteristic of milder climates1 such as the elephant1 the smaller rhinoceros1 and the deer4 ,in connection with these facts it should be noted that occasional remains of tundra vegetation and of trees are found beneath the loess1 while in the loess itself certain steppe animals1 such as the common gopher or spermaphyl1 are found4 ,penck interprets this as indicating a progressive desiccation culminating just before the oncoming of the next ice sheet4 ,the evidence advanced in favor of the hypothesis that the loess was formed when glaciation was near its maximum includes the fact that if the loess does not represent the outwash from the ,iowan ice1 there is little else that does1 and presumably there must have been outwash4 ,also the distribution of loess along the margins of streams suggests that much of the material came from the flood plains of overloaded streams flowing from the melting ice4 ,although there are some points in favor of the hypothesis that the loess originated 7#a7 in strictly inter-glacial times1 7#b7 at the end of inter-glacial epochs1 and 7#c7 at times of full glaciation1 each hypothesis is much weakened by evidence that supports the others4 ,the evidence of boreal animals seems to disprove the hypothesis that the loess was formed in the middle of a mild inter-glacial epoch4 ,on the other hand1 ,penck's hypothesis as to loess at the end of inter-glacial times fails to account for certain characteristics of the lowest part of the loess deposits and of the underlying topography4 ,instead of normal valleys and consequent prompt drainage such as ought to have developed before the end of a long inter-glacial epoch1 the surface on which the loess lies shows many undrained depressions4 ,some of these can be seen in exposed banks1 while many more are inferred from the presence of shells of pond snails here and there in the overlying loess4 ,the pond snails presumably lived in shallow pools occupying depressions in the uneven surface left by the ice4 ,another reason for questioning whether the loess was formed at the end of an inter-glacial epoch is that this hypothesis does not provide a reasonable origin for the material which composes the loess4 ,near the ,alps where the loess deposits are small and where glaciers probably persisted in the inter-glacial epochs and thus supplied flood plain material in large quantities1 this does not appear important4 ,in the broad upper ,mississippi ,basin1 however1 and also in the ,black ,earth region of ,russia there seems to be no way to get the large body of material composing the loess except by assuming the existence of great deserts to windward4 ,but there seems to be little or no evidence of such deserts where they could be effective4 ,the mineralogical character of the loess of ,iowan age proves that the material came from granitic rocks1 such as formed a large part of the drift4 ,the nearest extensive outcrops of granite are in the southwestern part of the ,united ,states1 nearly a thousand miles from ,iowa and ,illinois4 ,but the loess is thickest near the ice margin and thins toward the southwest and in other directions1 whereas if its source were the southwestern desert1 its maximum thickness would probably be near the margin of the desert4 ,the evidence cited above seems inconsistent not only with the hypothesis that the loess was formed at the end of an inter-glacial epoch1 but also with the idea that it originated at times of maximum glaciation either from river-borne sediments or from any other source4 ,a further and more convincing reason for this last conclusion is the probability and almost the certainty that when the ice advanced1 its front lay close to areas where the vegetation was not much thinner than that which today prevails under similar climatic conditions4 ,if the average temperature of glacial maxima was only #f deg4,c4 lower than that of today1 the conditions just beyond the ice front when it was in the loess region from southern ,illinois to ,minnesota would have been like those now prevailing in ,canada from ,new ,brunswick to ,winnipeg4 ,the vegetation there is quite different from the grassy1 semi-arid vegetation of which evidence is found in the loess4 ,the roots and stalks of such grassy vegetation are generally agreed to have helped produce the columnar structure which enables the loess to stand with almost vertical surfaces4 ,we are now ready to consider the probability that loess accumulated mainly during the retreat of the ice4 ,such a retreat exposed a zone of drift to the outflowing glacial winds4 ,most glacial hypotheses1 such as that of uplift1 or depleted carbon dioxide1 call for a gradual retreat of the ice scarcely faster than the vegetation could advance into the abandoned area4 ,under the solar-cyclonic hypothesis1 on the other hand1 the climatic changes may have been sudden and hence the retreat of the ice may have been much more rapid than the advance of vegetation4 ,now wind-blown materials are derived from places where vegetation is scanty4 ,scanty vegetation on good soil1 it is true1 is usually due to aridity1 but may also result because the time since the soil was exposed to the air has not been long enough for the soil to be sufficiently weathered to support vegetation4 ,even when weathering has had full opportunity1 as when sand bars1 mud flats1 and flood plains are exposed1 vegetation takes root only slowly4 ,moreover1 storms and violent winds may prevent the spread of vegetation1 as is seen on sandy beaches even in distinctly humid regions like ,new ,jersey and ,denmark4 ,thus it appears that unless the retreat of the ice were as slow as the advance of vegetation1 a barren area of more or less width must have bordered the retreating ice and formed an ideal source of loess4 ,several other lines of evidence seemingly support the conclusion that the loess was formed during the retreat of the ice4 ,for example1 ,shimek1 who has made almost a lifelong study of the ,iowan loess1 emphasizes the fact that there is often an accumulation of stones and pebbles at its base4 ,this suggests that the underlying till was eroded before the loess was deposited upon it4 ,the first reaction of most students is to assume that of course this was due to running water4 ,that is possible in many cases1 but by no means in all4 ,so widespread a sheet of gravel could not be deposited by streams without destroying the irregular basins and hollows of which we have seen evidence where the loess lies on glacial deposits4 ,on the other hand1 the wind is competent to produce a similar gravel pavement without disturbing the old topography4 ,desert pavements are a notable feature in most deserts4 ,on the edges of an ice sheet1 as ,hobbs has made us realize1 the commonest winds are outward4 ,they often attain a velocity of eighty miles an hour in ,antarctica and ,greenland4 ,such winds1 however1 usually decline rapidly in velocity only a few score miles from the ice4 ,thus their effect would be to produce rapid erosion of the freshly bared surface near the retreating ice4 ,the pebbles would be left behind as a pavement1 while sand and then loess would be deposited farther from the ice where the winds were weaker and where vegetation was beginning to take root4 ,such a decrease in wind velocity may explain the occasional vertical gradation from gravel through sand to coarse loess and then to normal fine loess4 ,as the ice sheet retreated the wind in any given place would gradually become less violent4 ,as the ice continued to retreat the area where loess was deposited would follow at a distance1 and thus each part of the gravel pavement would in turn be covered with the loess4 ,the hypothesis that loess is deposited while the ice is retreating is in accord with many other lines of evidence4 ,for example1 it accords with the boreal character of the mammal remains as described above4 ,again1 the advance of vegetation into the barren zone along the front of the ice would be delayed by the strong outblowing winds4 ,the common pioneer plants depend largely on the wind for the distribution of their seeds1 but the glacial winds would carry them away from the ice rather than toward it4 ,the glacial winds discourage the advance of vegetation in another way1 for they are drying winds1 as are almost all winds blowing from a colder to a warmer region4 ,the fact that remains of trees sometimes occur at the bottom of the loess probably means that the deposition of loess extended into the forests which almost certainly persisted not far from the ice4 ,this seems more likely than that a period of severe aridity before the advance of the ice killed the trees and made a steppe or desert4 ,penck's chief argument in favor of the formation of loess before the advance of the ice rather than after1 is that since loess is lacking upon the youngest drift sheet in ,europe it must have been formed before rather than after the last or ,wuerm advance of the ice4 ,this breaks down on two counts4 ,first1 on the corresponding 7,wisconsin7 drift sheet in ,america1 loess is present1--in small quantities to be sure1 but unmistakably present4 ,second1 there is no reason to assume that conditions were identical at each advance and retreat of the ice4 ,indeed1 the fact that in ,europe1 as in the ,united ,states1 nearly all the loess was formed at one time1 and only a little is associated with the other ice advances1 points clearly against ,penck's fundamental assumption that the accumulation of loess was due to the approach of a cold climate4 ,having seen that the loess was probably formed during the retreat of the ice1 we are now ready to inquire what conditions the cyclonic hypothesis would postulate in the loess areas during the various stages of a glacial cycle4 ,fig4 #b1 in ,chapter ,,iv1 gives the best idea of what would apparently happen in ,north ,america1 and events in ,europe would presumably be similar4 ,during the nine maximum years on which ,fig4 #b is based the sunspot numbers averaged seventy1 while during the nine minimum years they averaged less than five4 ,it seems fair to suppose that the maximum years represent the average conditions which prevailed in the past at times when the sun was in a median stage between the full activity which led to glaciation and the mild activity of the minimum years which appear to represent inter-glacial conditions4 ,this would mean that when a glacial period was approaching1 but before an ice sheet had accumulated to any great extent1 a crescent-shaped strip from ,montana through ,illinois to ,maine would suffer a diminution in storminess ranging up to #fj per cent as compared with inter-glacial conditions4 ,this is in strong contrast with an increase in storminess amounting to #ge or even #ajj per cent both in the boreal storm belt in ,canada and in the subtropical belt in the ,southwest4 ,such a decrease in storminess in the central ,united ,states would apparently be most noticeable in summer1 as is shown in ,earth and ,sun4 ,hence it would have a maximum effect in producing aridity4 ,this would favor the formation of loess1 but it is doubtful whether the aridity would become extreme enough to explain such vast deposits as are found throughout large parts of the ,mississippi ,basin4 ,that would demand that hundreds of thousands of square miles should become almost absolute desert1 and it is not probable that any such thing occurred4 ,nevertheless1 according to the cyclonic hypothesis the period immediately before the advent of the ice would be relatively dry in the central ,united ,states1 and to that extent favorable to the work of the wind4 ,as the climatic conditions became more severe and the ice sheet expanded1 the dryness and lack of storms would apparently diminish4 ,the reason1 as has been explained1 would be the gradual pushing of the storms southward by the high-pressure area which would develop over the ice sheet4 ,thus at the height of a glacial epoch there would apparently be great storminess in the area where the loess is found1 especially in summer4 ,hence the cyclonic hypothesis does not accord with the idea of great deposition of loess at the time of maximum glaciation4 ,finally we come to the time when the ice was retreating4 ,we have already seen that not only the river flood plains1 but also vast areas of fresh glacial deposits would be exposed to the winds1 and would remain without vegetation for a long time4 ,at that very time the retreat of the ice sheet would tend to permit the storms to follow paths determined by the degree of solar activity1 in place of the far southerly paths to which the high atmospheric pressure over the expanded ice sheet had previously forced them4 ,in other words1 the conditions shown in ,fig4 #b would tend to reappear when the sun's activity was diminishing and the ice sheet was retreating1 just as they had appeared when the sun was becoming more active and the ice sheet was advancing4 ,this time1 however1 the semi-arid conditions arising from the scarcity of storms would prevail in a region of glacial deposits and widely spreading river deposits1 few or none of which would be covered with vegetation4 ,the conditions would be almost ideal for eolian erosion and for the transportation of loess by the wind to areas a little more remote from the ice where grassy vegetation had made a start4 ,the cyclonic hypothesis also seems to offer a satisfactory explanation of variations in the amount of loess associated with the several glacial epochs4 ,it attributes these to differences in the rate of disappearance of the ice1 which in turn varied with the rate of decline of solar activity and storminess4 ,this is supposed to be the reason why the ,iowan loess deposits are much more extensive than those of the other epochs1 for the ,iowan ice sheet presumably accomplished part of its retreat much more suddenly than the other ice sheets4#eg ,the more sudden the retreat1 the greater the barren area where the winds could gather fine bits of dust4 ,temporary readvances may also have been so distributed and of such intensity that they frequently accentuated the condition shown in ,fig4 #b1 thus making the central ,united ,states dry soon after the exposure of great amounts of glacial debris4 ,the closeness with which the cyclonic hypothesis accords with the facts as to the loess is one of the pleasant surprises of the hypothesis4 ,the first draft of ,fig4 #b and the first outlines of the hypothesis were framed without thought of the loess4 ,yet so far as can now be seen1 both agree closely with the conditions of loess formation4 ,,footnotes3 ,footnote #ef3 ,chamberlin and ,salisbury3 ,geology1 #aijf1 ,vol4 ,,iii1 pp4 #dje-dab4 ,footnote #eg3 ,it may have retreated soon after reaching its maximum4 ,if so1 the general lack of thick terminal moraines would be explained4 ,see page #abb4 ,,chapter ,x ,,causes ,,of ,,mild ,,geological ,,climates ,in discussions of climate1 as of most subjects1 a peculiar psychological phenomenon is observable4 ,everyone sees the necessity of explaining conditions different from those that now exist1 but few realize that present conditions may be abnormal1 and that they need explanation just as much as do others4 ,because of this tendency glaciation has been discussed with the greatest fullness1 while there has been much neglect not only of the periods when the climate of the earth resembled that of the present1 but also of the vastly longer periods when it was even milder than now4 ,how important the periods of mild climate have been in geological times may be judged from the relative length of glacial compared with inter-glacial epochs1 and still more from the far greater relative length of the mild parts of periods and eras when compared with the severe parts4 ,recent estimates by ,r4 ,t4 ,chamberlin#eh indicate that according to the consensus of opinion among geologists the average inter-glacial epoch during the ,pleistocene was about five times as long as the average glacial epoch1 while the whole of a given glacial epoch averaged five times as long as the period when the ice was at a maximum4 ,climatic periods far milder1 longer1 and more monotonous than any inter-glacial epoch appear repeatedly during the course of geological history4 ,our task in this chapter is to explain them4 ,knowlton#ei has done geology a great service by collecting the evidence as to the mild type of climate which has again and again prevailed in the past4 ,he lays special stress on botanical evidence since that pertains to the variable atmosphere of the lands1 and hence furnishes a better guide than does the evidence of animals that lived in the relatively unchanging water of the oceans4 ,the nature of the evidence has already been indicated in various parts of this book4 ,it includes palms1 tree ferns1 and a host of other plants which once grew in regions which are now much too cold to support them4 ,with this must be placed the abundant reef-building corals and other warmth-loving marine creatures in latitudes now much too cold for them4 ,of a piece with this are the conditions of inter-glacial epochs in ,europe1 for example1 when elephants and hippopotamuses1 as well as many species of plants from low latitudes1 were abundant4 ,these conditions indicate not only that the climate was warmer than now1 but that the contrast from season to season was much less4 ,indeed1 ,knowlton goes so far as to say that relative uniformity1 mildness1 and comparative equability of climate1 accompanied by high humidity1 have prevailed over the greater part of the earth1 extending to1 or into1 polar circles1 during the greater part of geologic time--since1 at least1 the ,middle ,paleozoic4 ,this is the regular1 the ordinary1 the normal condition4 444 ,by many it is thought that one of the strongest arguments against a gradually cooling globe and a humid1 non-zonally disposed climate in the ages before the ,pleistocene is the discovery of evidences of glacial action practically throughout the entire geologic column4 ,hardly less than a dozen of these are now known1 ranging in age from ,huronian to ,eocene4 ,it seems to be a very general assumption by those who hold this view that these evidences of glacial activities are to be classed as ice ages1 largely comparable in effect and extent to the ,pleistocene refrigeration1 but as a matter of fact only three are apparently of a magnitude to warrant such designation4 ,these are the ,huronian glaciation1 that of the ',permo-,carboniferous1' and that of the ,pleistocene4 ,the others1 so far as available data go1 appear to be explainable as more or less local manifestations that had no widespread effect on1 for instance1 ocean temperatures1 distribution of life1 et cetera4 ,they might well have been of the type of ordinary mountain glaciers1 due entirely to local elevation and precipitation4 444 ,if the sun had been the principal source of heat in pre-,pleistocene time1 terrestrial temperatures would of necessity have been disposed in zones1 whereas the whole trend of this paper has been the presentation of proof that these temperatures were distinctly non-zonal4 ,therefore it seems to follow that the sun--at least the present small-angle sun--could not have been the sole or even the principal source of heat that warmed the early oceans4 ,knowlton is so strongly impressed by the widespread fossil floras that usually occur in the middle parts of the geological periods1 that as ,schuchert#c puts it1 he neglects the evidence of other kinds4 ,in the middle of the periods and eras the expansion of the warm oceans over the continents was greatest1 while the lands were small and hence had more or less insular climates of the oceanic type4 ,at such times1 the marine fauna agrees with the flora in indicating a mild climate4 ,large colony-forming foraminifera1 stony corals1 shelled cephalopods1 gastropods and thick-shelled bivalves1 generally the cemented forms1 were common in the ,far ,north and even in the ,arctic4 ,this occurred in the ,silurian1 ,devonian1 ,pennsylvanian1 and ,jurassic periods1 yet at other times1 such as the ,cretaceous and ,eocene1 such forms were very greatly reduced in variety in the northern regions or else wholly absent4 ,these things1 as ,schuchert#fj says1 can only mean that ,knowlton is right when he states that climatic zoning such as we have had since the beginning of the ,pleistocene did not obtain in the geologic ages prior to the ,pleistocene4 ,it does not mean1 however1 that there was a non-zonal arrangement and that the temperature of the oceans was everywhere the same and without widespread effect on the distribution of life4 ,students of paleontology hold that as far back as we can go in the study of plants1 there are evidences of seasons and of relatively cool climates in high latitudes4 ,the cycads1 for instance1 are one of the types most often used as evidence of a warm climate4 ,yet ,wieland1#fa who has made a lifelong study of these plants1 says that many of them might well grow in temperate to cool climates4 ,until far more is learned about them they should at least be held as valueless as indices of tropic climates4 ,the inference is that either they or their close relatives had the capacity to live in every clime4 ,there is also a suspicion that study of the associated ferns may compel revision of the long-accepted view of the universality of tropic climates throughout the ,mesozoic4 ,nathorst is quoted by ,wieland as saying1 ,i think 444 that during the time when the ,gingkophytes and ,cycadophytes dominated1 many of them must have adapted themselves for living in cold climates also4 ,of this ,i have not the least doubt4 ,another important line of evidence which ,knowlton and others have cited as a proof of the non-zonal arrangement of climate in the past1 is the vast red beds which are found in the ,proterozoic1 late ,silurian1 ,devonian1 ,permian1 and ,triassic1 and in some ,tertiary formations4 ,these are believed to resemble laterite1 a red and highly oxidized soil which is found in great abundance in equatorial regions4 ,knowlton does not attempt to show that the red beds present equatorial characteristics in other respects1 but bases his conclusion on the statement that red beds are not being formed at the present time in any desert region4 ,this is certainly an error4 ,as has already been said1 in both the ,transcaspian and ,takla ,makan deserts1 the color of the sand regularly changes from brown on the borders to pale red far out in the desert4 ,kuzzil ,kum1 or ,red ,sand1 is the native name4 ,the sands in the center of the desert apparently were originally washed down from the same mountains as those on the borders1 and time has turned them red4 ,since the same condition is reported from the ,arabian ,desert1 it seems that redness is characteristic of some of the world's greatest deserts4 ,moreover1 beds of salt and gypsum are regularly found in red beds1 and they can scarcely originate except in deserts1 or in shallow almost landlocked bays on the coasts of deserts1 as appears to have happened in the ,silurian where marine fossils are found interbedded with gypsum4 ,again1 ,knowlton says that red beds cannot indicate deserts because the plants found in them are not pinched or depauperate1 nor do they indicate xerophytic adaptations4 ,moreover1 very considerable deposits of coal are found in red beds in many parts of the world1 which implies the presence of swamps but little above sea-level4 ,students of desert botany are likely to doubt the force of these considerations4 ,as ,mac,dougal#fb has shown1 the variety of plants in deserts is greater than in moist regions4 ,not only do xerophytic desert species prevail1 but halophytes are present in the salty areas1 and hygrophytes in the wet swampy areas1 while ordinary mesophytes prevail along the water courses and are washed down from the mountains4 ,the ordinary plants1 not the xerophytes1 are the ones that are chiefly preserved since they occur in most abundance near streams where deposition is taking place4 ,so far as swamps are concerned1 few are of larger size than those of ,seistan in ,persia1 ,lop ,nor in ,chinese ,turkestan1 and certain others in the midst of the ,asiatic deserts4 ,streams flowing from the mountains into deserts are almost sure to form large swamps1 such as those along the ,tarim ,river in central ,asia4 ,lake ,chad in ,africa is another example4 ,in it1 too1 reeds are very numerous4 ,putting together the evidence on both sides in this disputed question1 it appears that throughout most of geological time there is some evidence of a zonal arrangement of climate4 ,the evidence takes the form of traces of cool climates1 of seasons1 and of deserts4 ,nevertheless1 there is also strong evidence that these conditions were in general less intense than at present and that times of relatively warm1 moist climate without great seasonal extremes have prevailed very widely during periods much longer than those when a zonal arrangement as marked as that of today prevailed4 ,as ,schuchert#fc puts it3 ,today the variation on land between the tropics and the poles is roughly between #aaj deg4 and -#fj deg4,f41 in the oceans between #he deg4 and #ca deg4,f4 ,in the geologic past the temperature of the oceans for the greater parts of the periods probably was most often between #he deg4 and #ee deg4,f41 while on land it may have varied between #ij deg4 and #j deg4,f4 ,at rare intervals the extremes were undoubtedly as great as they are today4 ,the conclusion is therefore that at all times the earth had temperature zones1 varying between the present-day intensity and times which were almost without such belts1 and at these latter times the greater part of the earth had an almost uniformly mild climate1 without winters4 ,it is these mild climates which we must now attempt to explain4 ,this leads us to inquire what would happen to the climate of the earth as a whole if the conditions which now prevail at times of few sunspots were to become intensified4 ,that they could become greatly intensified seems highly probable1 for there is good reason to think that aside from the sunspot cycle the sun's atmosphere is in a disturbed condition4 ,the prominences which sometimes shoot out hundreds of thousands of miles seem to be good evidence of this4 ,suppose that the sun's atmosphere should become very quiet4 ,this would apparently mean that cyclonic storms would be much less numerous and less severe than during the present times of sunspot minima4 ,the storms would also apparently follow paths in middle latitudes somewhat as they do now when sunspots are fewest4 ,the first effect of such a condition1 if we can judge from what happens at present1 would be a rise in the general temperature of the earth1 because less heat would be carried aloft by storms4 ,today1 as is shown in ,earth and ,sun1 a difference of perhaps #aj per cent in the average storminess during periods of sunspot maxima and minima is correlated with a difference of #c deg4,c4 in the temperature at the earth's surface4 ,this includes not only an actual lowering of #j4f deg4,c4 at times of sunspot maxima1 but the overcoming of the effect of increased insolation at such times1 an effect which ,abbot calculates as about #b4e deg4,c4 ,if the storminess were to be reduced to one-half or one-quarter its present amount at sunspot minima1 not only would the loss of heat by upward convection in storms be diminished1 but the area covered by clouds would diminish so that the sun would have more chance to warm the lower air4 ,hence the average rise of temperature might amount to as much at #e deg4 or #aj deg4,c4 ,another effect of the decrease in storminess would be to make the so-called westerly winds1 which are chiefly southwesterly in the northern hemisphere and northwesterly in the southern hemisphere1 more strong and steady than at present4 ,they would not continually suffer interruption by cyclonic winds from other directions1 as is now the case1 and would have a regularity like that of the trades4 ,this conclusion is strongly reenforced in a paper by ,clayton#fd which came to hand after this chapter had been completed4 ,from his studies of the solar constant and the temperature of the earth which are described in ,earth and ,sun1 he reaches the following conclusion3 ,the results of these researches have led me to believe3 #a4 ,that if there were no variation in solar radiation the atmospheric motions would establish a stable system with exchanges of air between equator and pole and between ocean and land1 in which the only variations would be daily and annual changes set in operation by the relative motions of the earth and sun4 #b4 ,the existing abnormal changes1 which we call weather1 have their origins chiefly1 if not entirely1 in the variations of solar radiation4 ,if cyclonic storms and weather were largely eliminated and if the planetary system of winds with its steady trades and southwesterlies became everywhere dominant1 the regularity and volume of the poleward-flowing currents1 such as the ,gulf ,stream and the ,atlantic ,drift in one ocean1 and the ,japanese ,current in another1 would be greatly increased4 ,how important this is may be judged from the work of ,helland-,hansen and ,nansen4#fe ,these authors find that with the passage of each cyclonic storm there is a change in the temperature of the surface water of the ,atlantic ,ocean4 ,winds at right angles to the course of the ,drift drive the water first in one direction and then in the other but do not advance it in its course4 ,winds with an easterly component1 on the other hand1 not only check the ,drift but reverse it1 driving the warm water back toward the southwest and allowing cold water to well up in its stead4 ,the driving force in the ,atlantic ,drift is merely the excess of the winds with a westerly component over those with an easterly component4 ,suppose that the numbers in ,fig4 #h represent the strength of the winds in a certain part of the ,north ,atlantic or ,north ,pacific1 that is1 the total number of miles moved by the air per year4 ,in quadrant ,a of the left-hand part all the winds move from a more or less southwesterly direction and produce a total movement of the air amounting to thirty units per year4 ,those coming from points between north and west move twenty-five units2 those between north and east1 twenty units2 and those between east and south1 twenty-five units4 ,since the movement of the winds in quadrants ,b and ,d is the same1 these winds have no effect in producing currents4 ,they merely move the water back and forth1 and thus give it time to lose whatever heat it has brought from more southerly latitudes4 ,on the other hand1 since the easterly winds in quadrant ,c do not wholly check the currents caused by the westerly winds of quadrant ,a1 the effective force of the westerly winds amounts to ten1 or the difference between a force of thirty in quadrant ,a and of twenty in quadrant ,c4 ,hence the water is moved forward toward the northeast1 as shown by the thick part of arrow ,a4 ,illustration3 ,fig4 #h4 ,effect of diminution of storms on movement of water4 ,now suppose that cyclonic storms should be greatly reduced in number so that in the zone of prevailing westerlies they were scarcely more numerous than tropical hurricanes now are in the trade-wind belt4 ,then the more or less southwesterly winds in quadrant ,a' in the right-hand part of ,fig4 #h would not only become more frequent but would be stronger than at present4 ,the total movement from that quarter might rise to sixty units1 as indicated in the figure4 ,in quadrants ,b' and ,d' the movement would fall to fifteen and in quadrant ,c' to ten4 ,b' and ,d' would balance one another as before4 ,the movement in ,a'1 however1 would exceed that in ,c' by fifty instead of ten4 ,in other words1 the current-making force would become five times as great as now4 ,the actual effect would be increased still more1 for the winds from the southwest would be stronger as well as steadier if there were no storms4 ,a strong wind which causes whitecaps has much more power to drive the water forward than a weaker wind which does not cause whitecaps4 ,in a wave without a whitecap the water returns to practically the original point after completing a circle beneath the surface4 ,in a wave with a whitecap1 however1 the cap moves forward4 ,any increase in velocity beyond the rate at which whitecaps are formed has a great influence upon the amount of water which is blown forward4 ,several times as much water is drifted forward by a persistent wind of twenty miles an hour as by a ten-mile wind4#ff ,in this connection a suggestion which is elaborated in ,chapter ,,xiii may be mentioned4 ,at present the salinity of the oceans checks the general deep-sea circulation and thereby increases the contrasts from zone to zone4 ,in the past1 however1 the ocean must have been fresher than now4 ,hence the circulation was presumably less impeded1 and the transfer of heat from low latitudes to high was facilitated4 ,consider now the magnitude of the probable effect of a diminution in storms4 ,today off the coast of ,norway in latitude #fe deg4,n4 and longitude #aj deg4,e41 the mean temperature in ,january is #b deg4,c4 and in ,july #ab deg4,c4 ,this represents a plus anomaly of about #bb deg4 in ,january and #b deg4 in ,july2 that is1 the ,norwegian coast is warmer than the normal for its latitude by these amounts4 ,suppose that in some past time the present distribution of lands and seas prevailed1 but ,norway was a lowland where extensive deposits could accumulate in great flood plains4 ,suppose1 also1 that the sun's atmosphere was so inactive that few cyclonic storms occurred1 steady winds from the west-southwest prevailed1 and strong1 uninterrupted ocean currents brought from the ,caribbean ,sea and ,gulf of ,mexico much greater supplies of warm water than at present4 ,the ,norwegian winters would then be warmer than now not only because of the general increase in temperature which the earth regularly experiences at sunspot minima1 but because the currents would accentuate this condition4 ,in summer similar conditions would prevail except that the warming effect of the winds and currents would presumably be less than in winter1 but this might be more than balanced by the increased heat of the sun during the long summer days1 for storms and clouds would be rare4 ,if such conditions raised the winter temperature only #h deg4,c4 and the summer temperature #d deg4,c41 the climate would be as warm as that of the northern island of ,new ,zealand 7latitude #ce deg4-#dc deg4,s474 ,the flora of that part of ,new ,zealand is subtropical and includes not only pines and beeches1 but palms and tree ferns4 ,a climate scarcely warmer than that of ,new ,zealand would foster a flora like that which existed in far northern latitudes during some of the milder geological periods4 ,if1 however1 the general temperature of the earth's surface were raised #e deg4 because of the scarcity of storms1 if the currents were strong enough so that they increased the present anomaly by #ej per cent1 and if more persistent sunshine in summer raised the temperature at that season about #d deg4,c41 the ,january temperature would be #ah deg4,c4 and the ,july temperature #bb deg4,c4 ,these figures perhaps make summer and winter more nearly alike than was ever really the case in such latitudes4 ,nevertheless1 they show that a diminution of storms and a consequent strengthening and steadying of the southwesterlies might easily raise the temperature of the ,norwegian coast so high that corals could flourish within the ,arctic ,circle4 ,another factor would cooeperate in producing mild temperatures in high latitudes during the winter1 namely1 the fogs which would presumably accumulate4 ,it is well known that when saturated air from a warm ocean is blown over the lands in winter1 as happens so often in the ,british ,islands and around the ,north ,sea1 fog is formed4 ,the effect of such a fog is indeed to shut out the sun's radiation1 but in high latitudes during the winter when the sun is low1 this is of little importance4 ,another effect is to retain the heat of the earth itself4 ,when a constant supply of warm water is being brought from low latitudes this blanketing of the heat by the fog becomes of great importance4 ,in the past1 whenever cyclonic storms were weak and westerly winds were correspondingly strong1 winter fogs in high latitudes must have been much more widespread and persistent than now4 ,the bearing of fogs on vegetation is another interesting point4 ,if a region in high latitudes is constantly protected by fog in winter1 it can support types of vegetation characteristic of fairly low latitudes1 for plants are oftener killed by dry cold than by moist cold4 ,indeed1 excessive evaporation from the plant induced by dry cold when the evaporated water cannot be rapidly replaced by the movement of sap is a chief reason why large plants are winterkilled4 ,the growing of transplanted palms on the coast of southwestern ,ireland1 in spite of its location in latitude #ej deg4,n41 is possible only because of the great fogginess in winter due to the marine climate4 ,the fogs prevent the escape of heat and ward off killing frosts4 ,the tree ferns in latitude #df deg4,s4 in ,new ,zealand1 already referred to1 are often similarly protected in winter4 ,therefore1 the relative frequency of fogs in high latitudes when storms were at a minimum would apparently tend not merely to produce mild winters but to promote tropical vegetation4 ,the strong steady trades and southwesterlies which would prevail at times of slight solar activity1 according to our hypothesis1 would have a pronounced effect on the water of the deep seas as well as upon that of the surface4 ,in the first place1 the deep-sea circulation would be hastened4 ,for convenience let us speak of the northern hemisphere4 ,in the past1 whenever the southwesterly winds were steadier than now1 as was probably the case when cyclonic storms were relatively rare1 more surface water than at present was presumably driven from low latitudes and carried to high latitudes4 ,this1 of course1 means that a greater volume of water had to flow back toward the equator in the lower parts of the ocean1 or else as a cool surface current4 ,the steady southwesterly winds1 however1 would interfere with south-flowing surface currents1 thus compelling the polar waters to find their way equatorward beneath the surface4 ,in low latitudes the polar waters would rise and their tendency would be to lower the temperature4 ,hence steadier westerlies would make for lessened latitudinal contrasts in climate not only by driving more warm water poleward but by causing more polar water to reach low latitudes4 ,at this point a second important consideration must be faced4 ,not only would the deep-sea circulation be hastened1 but the ocean depths might be warmed4 ,the deep parts of the ocean are today cold because they receive their water from high latitudes where it sinks because of low temperature4 ,suppose1 however1 that a diminution in storminess combined with other conditions should permit corals to grow in latitude #gj deg4,n4 ,the ocean temperature would then have to average scarcely lower than #bj deg4,c4 and even in the coldest month the water could scarcely fall below about #ae deg4,c4 ,under such conditions1 if the polar ocean were freely connected with the rest of the oceans1 no part of it would probably have a temperature much below #aj deg4,c41 for there would be no such thing as ice caps and snowfields to reflect the scanty sunlight and radiate into space what little heat there was4 ,on the contrary1 during the winter an almost constant state of dense fogginess would prevail4 ,so great would be the blanketing effect of this that a minimum monthly temperature of #aj deg4,c4 for the coldest part of the ocean may perhaps be too low for a time when corals thrived in latitude #gj deg44 ,the temperature of the ocean depths cannot permanently remain lower than that of the coldest parts of the surface4 ,temporarily this might indeed happen when a solar change first reduced the storminess and strengthened the westerlies and the surface currents4 ,gradually1 however1 the persistent deep-sea circulation would bring up the colder water in low latitudes and carry downward the water of medium temperature at the coldest part of the surface4 ,thus in time the whole body of the ocean would become warm4 ,the heat which at present is carried away from the earth's surface in storms would slowly accumulate in the oceans4 ,as the process went on1 all parts of the ocean's surface would become warmer1 for equatorial latitudes would be less and less cooled by cold water from below1 while the water blown from low latitudes to high would be correspondingly warmer4 ,the warming of the ocean would come to an end only with the attainment of a state of equilibrium in which the loss of heat by radiation and evaporation from the ocean's surface equaled the loss which under other circumstances would arise from the rise of warm air in cyclonic storms4 ,when once the oceans were warmed1 they would form an extremely strong conservative force tending to preserve an equable climate in all latitudes and at all seasons4 ,according to the solar cyclonic hypothesis such conditions ought to have prevailed throughout most of geological time4 ,only after a strong and prolonged solar disturbance with its consequent storminess would conditions like those of today be expected4 ,in this connection another possibility may be mentioned4 ,it is commonly assumed that the earth's axis is held steadily in one direction by the fact that the rotating earth is a great gyroscope4 ,having been tilted to a certain position1 perhaps by some extraneous force1 the axis is supposed to maintain that position until some other force intervenes4 ,cordeiro1#fg however1 maintains that this is true only of an absolutely rigid gyroscope4 ,he believes that it is mathematically demonstrable that if an elastic gyroscope be gradually tilted by some extraneous force1 and if that force then ceases to act1 the gyroscope as a whole will oscillate back and forth4 ,the earth appears to be slightly elastic4 ,cordeiro therefore applies his formulae to it1 on the following assumptions3 7#a7 ,that the original position of the axis was nearly vertical to the plane of the ecliptic in which the earth revolves around the sun2 7#b7 that at certain times the inclination has been even greater than now2 and 7#c7 that the position of the axis with reference to the earth has not changed to any great extent1 that is1 the earth's poles have remained essentially stationary with reference to the earth1 although the whole earth has been gyroscopically tilted back and forth repeatedly4 ,with a vertical axis the daylight and darkness in all parts of the earth would be of equal duration1 being always twelve hours4 ,there would be no seasons1 and the climate would approach the average condition now experienced at the two equinoxes4 ,on the whole the climate of high latitudes would give the impression of being milder than now1 for there would be less opportunity for the accumulation of snow and ice with their strong cooling effect4 ,on the other hand1 if the axis were tilted more than now1 the winter nights would be longer and the winters more severe than at present1 and there would be a tendency toward glaciation4 ,thus ,cordeiro accounts for alternating mild and glacial epochs4 ,the entire swing from the vertical position to the maximum inclination and back to the vertical may last millions of years depending on the earth's degree of elasticity4 ,the swing beyond the vertical position in the other direction would be equally prolonged4 ,since the axis is now supposed to be much nearer its maximum than its minimum degree of tilting1 the duration of epochs having a climate more severe than that of the present would be relatively short1 while the mild epochs would be long4 ,cordeiro's hypothesis has been almost completely ignored4 ,one reason is that his treatment of geological facts1 and especially his method of riding rough-shod over widely accepted conclusions1 has not commended his work to geologists4 ,therefore they have not deemed it worth while to urge mathematicians to test the assumptions and methods by which he reached his results4 ,it is perhaps unfair to test ,cordeiro by geology1 for he lays no claim to being a geologist4 ,in mathematics he labors under the disadvantage of having worked outside the usual professional channels1 so that his work does not seem to have been subjected to sufficiently critical analysis4 ,without expressing any opinion as to the value of ,cordeiro's results we feel that the subject of the earth's gyroscopic motion and of a possible secular change in the direction of the axis deserves investigation for two chief reasons4 ,in the first place1 evidences of seasonal changes and of seasonal uniformity seem to occur more or less alternately in the geological record4 ,second1 the remarkable discoveries of ,garner and ,allard#fh show that the duration of daylight has a pronounced effect upon the reproduction of plants4 ,we have referred repeatedly to the tree ferns1 corals1 and other forms of life which now live in relatively low latitudes and which cannot endure strong seasonal contrasts1 but which once lived far to the north4 ,on the other hand1 ,sayles1#fi for example1 finds that microscopical examination of the banding of ancient shales and slates indicates distinct seasonal banding like that of recent ,pleistocene clays or of the ,squantum slate formed during or near the ,permian glacial period4 ,such seasonal banding is found in rocks of various ages3 7a7 ,huronian1 in cobalt shales previously reported by ,coleman2 7b7 late ,proterozoic or early ,cambrian in ,hiwassee slate2 7c7 lower ,cambrian1 in ,georgian slates of ,vermont2 7d7 lower ,ordovician1 in ,georgia 7,rockmart slate71 ,tennessee 7,athens shale71 ,vermont 7slates71 and ,quebec 7,beekmantown formation72 and 7e7 ,permian in ,massachusetts 7,squantum slate74 ,how far the periods during which such evidence of seasons was recorded really alternated with mild periods1 when tropical species lived in high latitudes and the contrast of seasons was almost or wholly lacking1 we have as yet no means of knowing4 ,if periods characterized by marked seasonal changes should be found to have alternated with those when the seasons were of little importance1 the fact would be of great geological significance4 ,the discoveries of ,garner and ,allard as to the effect of light on reproduction began with a peculiar tobacco plant which appeared in some experiments at ,washington4 ,the plant grew to unusual size1 and seemed to promise a valuable new variety4 ,it formed no seeds1 however1 before the approach of cold weather4 ,it was therefore removed to a greenhouse where it flowered and produced seed4 ,in succeeding years the flowering was likewise delayed till early winter1 but finally it was discovered that if small plants were started in the greenhouse in the early fall they flowered at the same time as the large ones4 ,experiments soon demonstrated that the time of flowering depends largely upon the length of the daily period when the plants are exposed to light4 ,the same is true of many other plants1 and there is great variety in the conditions which lead to flowering4 ,some plants1 such as witch hazel1 appear to be stimulated to bloom by very short days1 while others1 such as evening primrose1 appear to require relatively long days4 ,so sensitive are plants in this respect that ,garner and ,allard1 by changing the length of the period of light1 have caused a flowerbud in its early stages not only to stop developing but to return once more to a vegetative shoot4 ,common iris1 which flowers in ,may and ,june1 will not blossom under ordinary conditions when grown in the greenhouse in winter1 even under the same temperature conditions that prevail in early summer4 ,again1 one variety of soy beans will regularly begin to flower in ,june of each year1 a second variety in ,july1 and a third in ,august1 when all are planted on the same date4 ,there are no temperature differences during the summer months which could explain these differences in time of flowering2 and1 since internal causes alone cannot be accepted as furnishing a satisfactory explanation1 some external factor other than temperature must be responsible4 ,the ordinary varieties of cosmos regularly flower in the fall in northern latitudes if they are planted in the spring or summer4 ,if grown in a warm greenhouse during the winter months the plants also flower readily1 so that the cooler weather of fall is not a necessary condition4 ,if successive plantings of cosmos are made in the greenhouse during the late winter and early spring months1 maintaining a uniform temperature throughout1 the plantings made after a certain date will fail to blossom promptly1 but1 on the contrary1 will continue to grow till the following fall1 thus flowering at the usual season for this species4 ,this curious reversal of behavior with advance of the season cannot be attributed to change in temperature4 ,some other factor is responsible for the failure of cosmos to blossom during the summer months4 ,in this respect the behavior of cosmos is just the opposite of that observed in iris4 ,certain varieties of soy beans change their behavior in a peculiar manner with advance of the summer season4 ,the variety known as ,biloxi1 for example1 when planted early in the spring in the latitude of ,washington1 ,d4 ,c41 continues to grow throughout the summer1 flowering in ,september4 ,the plants maintain growth without flowering for fifteen to eighteen weeks1 attaining a height of five feet or more4 ,as the dates of successive plantings are moved forward through the months of ,june and ,july1 however there is a marked tendency for the plants to cut short the period of growth which precedes flowering4 ,this means1 of course1 that there is a tendency to flower at approximately the same time of year regardless of the date of planting4 ,as a necessary consequence1 the size of the plants at the time of flowering is reduced in proportion to the delay in planting4 ,the bearing of this on geological problems lies in a query which it raises as to the ability of a genus or family of plants to adapt itself to days of very different length from those to which it is wonted4 ,could tree ferns1 ginkgos1 cycads1 and other plants whose usual range of location never subjects them to daylight for more than perhaps fourteen hours or less than ten1 thrive and reproduce themselves if subjected to periods of daylight ranging all the way from nothing up to about twenty-four hours8 ,no answer to this is yet possible1 but the question raises most interesting opportunities of investigation4 ,if ,cordeiro is right as to the earth's elastic gyroscopic motion1 there may have been certain periods when a vertical or almost vertical axis permitted the days to be of almost equal length at all seasons in all latitudes4 ,if such an absence of seasons occurred when the lands were low1 when the oceans were extensive and widely open toward the poles1 and when storms were relatively inactive1 the result might be great mildness of climate such as appears sometimes to have prevailed in the middle of geological eras4 ,suppose on the other hand that the axis should be tilted more than now1 and that the lands should be widely emergent and the storm belt highly active in low latitudes1 perhaps because of the activity of the sun4 ,the conditions might be favorable for glaciation at latitudes as low as those where the ,permo-,carboniferous ice sheets appear to have centered4 ,the possibilities thus suggested by ,cordeiro's hypothesis are so interesting that the gyroscopic motion of the earth ought to be investigated more thoroughly4 ,even if no such gyroscopic motion takes place1 however1 the other causes of mild climate discussed in this chapter may be enough to explain all the observed phenomena4 ,many important biological consequences might be drawn from this study of mild geological climates1 but this book is not the place for them4 ,in the first chapter we saw that one of the most remarkable features of the climate of the earth is its wonderful uniformity through hundreds of millions of years4 ,as we come down through the vista of years the mild geological periods appear to represent a return as nearly as possible to this standard condition of uniformity4 ,certain changes of the earth itself1 as we shall see in the next chapter1 may in the long run tend slightly to change the exact conditions of this climatic standard1 as we might perhaps call it4 ,yet they act so slowly that their effect during hundreds of millions of years is still open to question4 ,at most they seem merely to have produced a slight increase in diversity from season to season and from zone to zone4 ,the normal climate appears still to be of a milder type than that which happens to prevail at present4 ,some solar condition1 whose possible nature will be discussed later1 seems even now to cause the number of cyclonic storms to be greater than normal4 ,hence the earth's climate still shows something of the great diversity of seasons and of zones which is so marked a characteristic of glacial epochs4 ,,footnotes3 ,footnote #eh3 ,rollin ,t4 ,chamberlin3 ,personal ,communication4 ,footnote #ei3 ,f4 ,h4 ,knowlton3 ,evolution of ,geologic ,climates2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #cj1 #aiai1 pp4 #dii-eff4 ,footnote #fj3 ,chas4 ,schuchert3 ,review of ,knowlton's ,evolution of ,geological ,climates1 in ,am4 ,jour4 ,sci41 #aiba4 ,footnote #fa3 ,g4 ,r4 ,wieland3 ,distribution and ,relationships of the ,cycadeoids2 ,am4 ,jour4 ,bot41 ,vol4 #g1 #aibj1 pp4 #abe-ade4 ,footnote #fb3 ,d4 ,t4 ,mac,dougal3 ,botanical ,features of ,north ,american ,deserts2 ,carnegie ,instit4 of ,wash41 ,no4 #ii1 #aijh4 ,footnote #fc3 ,loc4 cit4 ,footnote #fd3 ,h4 ,h4 ,clayton3 ,variation in ,solar ,radiation and the ,weather2 ,smiths4 ,misc4 ,coll41 ,vol4 #ga1 ,no4 #c1 ,washington1 #aibj4 ,footnote #fe3 ,b4 ,helland ,hansen and ,f4 ,nansen3 ,temperature ,variations in the ,north ,atlantic ,ocean and in the ,atmosphere2 ,misc4 ,coll41 ,smiths4 ,inst41 ,vol4 #gj1 ,no4 #d1 ,washington1 #aibj4 ,footnote #ff3 ,the climatic significance of ocean currents is well discussed in ,croll's ,climate and ,time1 #ahge1 and his ,climate and ,cosmogony1 #ahhi4 ,footnote #fg3 ,f4 ,j4 ,b4 ,cordeiro3 ,the ,gyroscope1 #aiac4 ,footnote #fh3 ,w4 ,w4 ,garner and ,h4 ,a4 ,allard3 ,flowering and ,fruition of ,plants as ,controlled by ,length of ,day2 ,yearbook ,dept4 ,agri41 #aibj1 pp4 #cgg-djj4 ,footnote #fi3 ,report of ,committee on ,sedimentation1 ,national ,research ,council1 ,april1 #aibb4 ,,chapter ,,xi ,,terrestrial ,,causes ,,of ,,climatic ,,changes ,the major portion of this book has been concerned with the explanation of the more abrupt and extreme changes of climate4 ,this chapter and the next consider two other sorts of climatic changes1 the slight secular progression during the hundreds of millions of years of recorded earth history1 and especially the long slow geologic oscillations of millions or tens of millions of years4 ,it is generally agreed among geologists that the progressive change has tended toward greater extremes of climate2 that is1 greater seasonal contrasts1 and greater contrasts from place to place and from zone to zone4#gj ,the slow cyclic changes have been those that favored widespread glaciation at one extreme near the ends of geologic periods and eras1 and mild temperatures even in subpolar regions at the other extreme during the medial portions of the periods4 ,as has been pointed out in an earlier chapter1 it has often been assumed that all climatic changes are due to terrestrial causes4 ,we have seen1 however1 that there is strong evidence that solar variations play a large part in modifying the earth's climate4 ,we have also seen that no known terrestrial agency appears to be able to produce the abrupt changes noted in recent years1 the longer cycles of historical times1 or geological changes of the shorter type1 such as glaciation4 ,nevertheless1 terrestrial changes doubtless have assisted in producing both the progressive change and the slow cyclic changes recorded in the rocks1 and it is the purpose of this chapter and the two that follow to consider what terrestrial changes have taken place and the probable effect of such changes4 ,the terrestrial changes that have a climatic significance are numerous4 ,some1 such as variations in the amount of volcanic dust in the higher air1 have been considered in an earlier chapter4 ,others are too imperfectly known to warrant discussion1 and in addition there are presumably others which are entirely unknown4 ,doubtless some of these little known or unknown changes have been of importance in modifying climate4 ,for example1 the climatic influence of vegetation1 animals1 and man may be appreciable4 ,here1 however1 we shall confine ourselves to purely physical causes1 which will be treated in the following order3 ,first1 those concerned with the solid parts of the earth1 namely3 7,i7 amount of land2 7,,ii7 distribution of land2 7,,iii7 height of land2 7,,iv7 lava flows2 and 7,v7 internal heat4 ,second1 those which arise from the salinity of oceans1 and third1 those depending on the composition and amount of atmosphere4 ,the terrestrial change which appears indirectly to have caused the greatest change in climate is the contraction of the earth4 ,the problem of contraction is highly complex and is as yet only imperfectly understood4 ,since only its results and not its processes influence climate1 the following section as far as page #aif is not necessary to the general reader4 ,it is inserted in order to explain why we assume that there have been oscillations between certain types of distribution of the lands4 ,the extent of the earth's contraction may be judged from the shrinkage indicated by the shortening of the rock formations in folded mountains such as the ,alps1 ,juras1 ,appalachians1 and ,caucasus4 ,geologists are continually discovering new evidence of thrust faults of great magnitude where masses of rock are thrust bodily over other rocks1 sometimes for many miles4 ,therefore1 the estimates of the amount of shrinkage based on the measurements of folds and faults need constant revision upward4 ,nevertheless1 they have already reached a considerable figure4 ,for example1 in #aiai1 ,professor ,a4 ,heim estimated the shortening of the meridian passing through the modern ,alps and the ancient ,hercynian and ,caledonian mountains as fully a thousand miles in ,europe1 and over five hundred miles for the rest of this meridian4#ga ,this is a radial shortening of about #bej miles4 ,possibly the shrinkage has been even greater than this4 ,chamberlin#gb has compared the density of the earth1 moon1 ,mars1 and ,venus with one another1 and found it probable that the radial shrinkage of the earth may be as much as #egj miles4 ,this result is not so different from ,heim's as appears at first sight1 for ,heim made no allowance for unrecognized thrust faults and for the contraction incident to metamorphism4 ,moreover1 ,heim did not include shrinkage during the first half of geological time before the above-mentioned mountain systems were upheaved4 ,according to a well-established law of physics1 contraction of a rotating body results in more rapid rotation and greater centrifugal force4 ,these conditions must increase the earth's equatorial bulge and thereby cause changes in the distribution of land and water4 ,opposed to the rearrangement of the land due to increased rotation caused by contraction1 there has presumably been another rearrangement due to tidal retardation of the earth's rotation and a consequent lessening of the equatorial bulge4 ,g4 ,h4 ,darwin long ago deduced a relatively large retardation due to lunar tides4 ,a few years ago ,w4 ,d4 ,mac,millan1 on other assumptions1 deduced only a negligible retardation4 ,still more recently ,taylor#gc has studied the tides of the ,irish ,sea1 and his work has led ,jeffreys#gd and ,brown#ge to conclude that there has been considerable retardation1 perhaps enough1 according to ,brown1 to equal the acceleration due to the earth's contraction4 ,from a prolonged and exhaustive study of the motions of the moon ,brown concludes that tidal friction or some other cause is now lengthening the day at the rate of one second per thousand years1 or an hour in almost four million years if the present rate continues4 ,he makes it clear that the retardation due to tides would not correspond in point of time with the acceleration due to contraction4 ,the retardation would occur slowly1 and would take place chiefly during the long quiet periods of geologic history1 while the acceleration would occur rapidly at times of diastrophic deformation4 ,as a consequence1 the equatorial bulge would alternately be reduced at a slow rate1 and then somewhat suddenly augmented4 ,the less rigid any part of the earth is1 the more quickly it responds to the forces which lead to bulging or which tend to lessen the bulge4 ,since water is more fluid than land1 the contraction of the earth and the tidal retardation presumably tend alternately to increase and decrease the amount of water near the equator more than the amount of land4 ,thus1 throughout geological history we should look for cyclic changes in the relative area of the lands within the tropics and similar changes of opposite phase in higher latitudes4 ,the extent of the change would depend upon 7a7 the amount of alteration in the speed of rotation1 and 7b7 the extent of low land in low latitudes and of shallow sea in high latitudes4 ,according to ,slichter's tables1 if the earth should rotate in twenty-three hours instead of twenty-four1 the great ,amazon lowland would be submerged by the inflow of oceanic water1 while wide areas in ,hudson ,bay1 the ,north ,sea1 and other northern regions1 would become land because the ocean water would flow away from them4#gf ,following the prompt equatorward movement of water which would occur as the speed of rotation increased1 there must also be a gradual movement or creepage of the solid rocks toward the equator1 that is1 a bulging of the ocean floor and of the lands in low latitudes1 with a consequent emergence of the lands there and a relative rise of sea level in higher latitudes4 ,tidal retardation would have a similar effect4 ,suess#gg has described widespread elevated strand lines in the tropics which he interprets as indicating a relatively sudden change in sea level1 though he does not suggest a cause of the change4 ,however1 in speaking of recent geological times1 ,suess reports that a movement more recent than the old strands was an accumulation of water toward the equator1 a diminution toward the poles1 and 7it appears7 as though this last movement were only one of the many oscillations which succeed each other with the same tendency1 i4e41 with a positive excess at the equator1 a negative excess at the poles4 7,vol4 ,,ii1 p4 #eea47 ,this creepage of the rocks equatorward seemingly might favor the growth of mountains in tropical and subtropical regions1 because it is highly improbable that the increase in the bulge would go on in all longitudes with perfect uniformity4 ,where it went on most rapidly mountains would arise4 ,that such irregularity of movement has actually occurred is suggested not only by the fact that many ,cenozoic and older mountain ranges extend east and west1 but by the further fact that these include some of our greatest ranges1 many of which are in fairly low latitudes4 ,the ,himalayas1 the ,javanese ranges1 and the half-submerged ,caribbean chains are examples4 ,such mountains suggest a thrust in a north and south direction which is just what would happen if the solid mass of the earth were creeping first equatorward and then poleward4 ,a fact which is in accord with the idea of a periodic increase in the oceans in low latitudes because of renewed bulging at the equator is the exposure in moderately high latitudes of the greatest extent of ancient rocks4 ,this seems to mean that in low latitudes the frequent deepening of the oceans has caused the old rocks to be largely covered by sediments1 while the old lands in higher latitudes have been left more fully exposed to erosion4 ,another suggestion of such periodic equatorward movements of the ocean water is found in the reported contrast between the relative stability with which the northern part of ,north ,america has remained slightly above sea level except at times of widespread submergence1 while the southern parts have suffered repeated submergence alternating with great emergence4#gh ,furthermore1 although the northern part of ,north ,america has been generally exposed to erosion since the ,proterozoic1 it has supplied much less sediment than have the more southern land areas4#gi ,this apparently means that much of ,canada has stood relatively low1 while repeated and profound uplift alternating with depression has occurred in subtropical latitudes1 apparently in adjustment to changes in the earth's speed of rotation4 ,the uplifts generally followed the times of submergence due to equatorward movement of the water1 though the buckling of the crust which accompanies shrinkage doubtless caused some of the submergence4 ,the evidence that northern ,north ,america stood relatively low throughout much of geological time depends not only on the fact that little sediment came to the south from the north1 but also on the fact that at times of especially widespread epicontinental seas1 the submergence was initiated at the north4#hj ,this is especially true for ,ordovician1 ,silurian1 ,devonian1 and ,jurassic times in ,north ,america4 ,general submergence of this kind is supposed to be due chiefly to the overflowing of the ocean when its level is slowly raised by the deposition of sediment derived from the erosion of what once were continental highlands but later are peneplains4 ,the fact that such submergence began in high latitudes1 however1 seems to need a further explanation4 ,the bulging of the rock sphere at the equator and the consequent displacement of some of the water in low latitudes would furnish such an explanation1 as would also a decrease in the speed of rotation induced by tidal retardation1 if that retardation were great enough and rapid enough to be geologically effective4 ,the climatic effects of the earth's contraction1 which we shall shortly discuss1 are greatly complicated by the fact that contraction has taken place irregularly4 ,such irregularity has occurred in spite of the fact that the processes which cause contraction have probably gone on quite steadily throughout geological history4 ,these processes include the chemical reorganization of the minerals of the crust1 a process which is illustrated by the metamorphism of sedimentary rocks into crystalline forms4 ,the escape of gases through volcanic action or otherwise has been another important process4 ,although the processes which cause contraction probably go on steadily1 their effect1 as ,chamberlin#ha and others have pointed out1 is probably delayed by inertia4 ,thus the settling of the crust or its movement on a large scale is delayed4 ,perhaps the delay continues until the stresses become so great that of themselves they overcome the inertia1 or possibly some outside agency1 whose nature we shall consider later1 reenforces the stresses and gives the slight impulse which is enough to release them and allow the earth's crust to settle into a new state of equilibrium4 ,when contraction proceeds actively1 the ocean segments1 being largest and heaviest1 are likely to settle most1 resulting in a deepening of the oceans and an emergence of the lands4 ,following each considerable contraction there would be an increase in the speed of rotation4 ,the repeated contractions with consequent growth of the equatorial bulge would alternate with long quiet periods during which tidal retardation would again decrease the speed of rotation and hence lessen the bulge4 ,the result would be repeated changes of distribution of land and water1 with consequent changes in climate4 ,i4 ,we shall now consider the climatic effect of the repeated changes in the relative amounts of land and water which appear to have resulted from the earth's contraction and from changes in its speed of rotation4 ,during many geologic epochs a larger portion of the earth was covered with water than at present4 ,for example1 during at least twelve out of about twenty epochs1 ,north ,america has suffered extensive inundations1#hb and in general the extensive submergence of ,europe1 the other area well known geologically1 has coincided with that of ,north ,america4 ,at other times1 the ocean has been less extensive than now1 as for example during the recent glacial period1 and probably during several of the glacial periods of earlier date4 ,each of the numerous changes in the relative extent of the lands must have resulted in a modification of climate4#hc ,this modification would occur chiefly because water becomes warm far more slowly than land1 and cools off far more slowly4 ,an increase in the lands would cause changes in several climatic conditions4 7a7 ,the range of temperature between day and night and between summer and winter would increase1 for lands become warmer by day and in summer than do oceans1 and cooler at night and in winter4 ,the higher summer temperature when the lands are widespread is due chiefly to the fact that the land1 if not snow-covered1 absorbs more of the sun's radiant energy than does the ocean1 for its reflecting power is low4 ,the lower winter temperature when lands are widespread occurs not only because they cool off rapidly but because the reduced oceans cannot give them so much heat4 ,moreover1 the larger the land1 the more generally do the winds blow outward from it in winter and thus prevent the ocean heat from being carried inland4 ,so long as the ocean is not frozen in high latitudes1 it is generally the chief source of heat in winter1 for the nights are several months long near the poles1 and even when the sun does shine its angle is so low that reflection from the snow is very great4 ,furthermore1 although on the average there is more reflection from water than from land1 the opposite is true in high latitudes in winter when the land is snow-covered while the ocean is relatively dark and is roughened by the waves4 ,another factor in causing large lands to have extremely low temperature in winter is the fact that in proportion to their size they are less protected by fog and cloud than are smaller areas4 ,the belt of cloud and fog which is usually formed when the wind blows from the ocean to the relatively cold land is restricted to the coastal zone4 ,thus the larger the land1 the smaller the fraction in which loss of heat by radiation is reduced by clouds and fogs4 ,hence an increase in the land area is accompanied by an increase in the contrasts in temperature between land and water4 7b7 ,the contrasts in temperature thus produced must cause similar contrasts in atmospheric pressure1 and hence stronger barometric gradients4 7c7 ,the strong gradients would mean strong winds1 flowing from land to sea or from sea to land4 7d7 ,local convection would also be strengthened in harmony with the expansion of the lands1 for the more rapid heating of land than of water favors active convection4 7e7 ,as the extent of the ocean diminished1 there would normally be a decrease in the amount of water vapor for three reasons3 7#a7 ,evaporation from the ocean is the great source of water vapor4 ,other conditions being equal1 the smaller the ocean becomes1 the less the evaporation4 7#b7 ,the amount of water vapor in the air diminishes as convection increases1 since upward convection is a chief method by which condensation and precipitation are produced1 and water vapor removed from the atmosphere4 7#c7 ,nocturnal cooling sufficient to produce dew and frost is very much more common upon land than upon the ocean4 ,the formation of dew and frost diminishes the amount of water vapor at least temporarily4 7f7 ,any diminution in water vapor produced in these ways1 or otherwise1 is significant because water vapor is the most essential part of the atmosphere so far as regulation of temperature is concerned4 ,it tends to keep the days from becoming hot or the nights cold4 ,therefore any decrease in water vapor would increase the diurnal and seasonal range of temperature1 making the climate more extreme and severe4 ,thus a periodic increase in the area of the continents would clearly make for periodic increased climatic contrasts1 with great extremes1 a type of climatic change which has recurred again and again4 ,indeed1 each great glaciation accompanied or followed extensive emergence of the lands4#hd ,whether or not there has been a progressive increase from era to era in the area of the lands is uncertain4 ,good authorities disagree widely4 ,there is no doubt1 however1 that at present the lands are more extensive than at most times in the past1 though smaller1 perhaps1 than at certain periods4 ,the wide expanse of lands helps explain the prominence of seasons at present as compared with the past4 ,,ii4 ,the contraction of the earth1 as we have seen1 has produced great changes in the distribution as well as in the extent of land and water4 ,large parts of the present continents have been covered repeatedly by the sea1 and extensive areas now covered with water have been land4 ,in recent geological times1 that is1 during the ,pliocene and ,pleistocene1 much of the present continental shelf1 the zone less than #fjj feet below sea level1 was land4 ,if the whole shelf had been exposed1 the lands would have been greater than at present by an area larger than ,north ,america4 ,when the lands were most elevated1 or a little earlier1 ,north ,america was probably connected with ,asia and almost with ,europe4 ,asia in turn was apparently connected with the larger ,east ,indian islands4 ,in much earlier times land occupied regions where now the ocean is fairly deep4 ,groups of islands1 such as the ,east ,indies and ,malaysia and perhaps the ,west ,indies1 were united into widespreading land masses4 ,figs4 #g and #i1 illustrating the paleography of the ,permian and the ,cretaceous periods1 respectively1 indicate a land distribution radically different from that of today4 ,so far as appears from the scattered facts of geological history1 the changes in the distribution of land seem to have been marked by the following characteristics3 7#a7 ,accompanying the differentiation of continental and oceanic segments of the earth's crust1 the oceans have become somewhat deeper1 and their basins perhaps larger1 while the continents1 on the average1 have been more elevated and less subject to submergence4 ,hence there have been less radical departures from the present distribution during the relatively recent ,cenozoic era than in the ancient ,paleozoic because the submergence of continental areas has become less general and less frequent4 ,for example1 the last extensive epeiric or interior sea in ,north ,america was in the ,cretaceous1 at least ten million years ago1 and according to ,barrell perhaps fifty million1 while in ,europe1 according to de ,lapparent1#he a smaller share of the present continent has been submerged since the ,cretaceous than before4 ,indeed1 as in ,north ,america1 the submergence has decreased on the average since the ,paleozoic era4 7#b7 ,the changes in distribution of land which have taken place during earth history have been cyclic4 ,repeatedly1 at the close of each of the score or so of geologic periods1 the continents emerged more or less1 while at the close of the groups of periods known as eras1 the lands were especially large and emergent4 ,after each emergence1 a gradual encroachment of the sea took place1 and toward the close of several of the earlier periods1 the sea appears to have covered a large fraction of the present land areas4 7#c7 ,on the whole1 the amount of land in the middle and high latitudes of the northern hemisphere appears to have increased during geologic time4 ,such an increase does not require a growth of the continents1 however1 in the broader sense of the term1 but merely that a smaller fraction of the continent and its shelf should be submerged4 7#d7 ,in tropical latitudes1 on the other hand1 the extent of the lands seems to have decreased1 apparently by the growth of the ocean basins4 ,south ,america and ,africa are thought by many students to have been connected1 and ,africa was united with ,india via ,madagascar1 as is suggested in ,fig4 #i4 ,the most radical cyclic as well as the most radical progressive changes in land distribution also seem to have taken place in tropical regions4#hf ,illustration3 ,fig4 #i4 ,cretaceous ,paleogeography4 7,after ,schuchert47 ,although there is much evidence of periodic increase of the sea in equatorial latitudes and of land in high latitudes1 it has remained for the zooelogist ,metcalf to present a very pretty bit of evidence that at certain times submergence along the equator coincided with emergence in high latitudes1 and vice versa4 ,certain fresh water frogs which carry the same internal parasite are confined to two widely separated areas in tropical and south temperate ,america and in ,australia4 ,the extreme improbability that both the frogs and the parasites could have originated independently in two unconnected areas and could have developed by convergent evolution so that they are almost identical in the two continents makes it almost certain that there must have been a land connection between ,south ,america and ,australia1 presumably by way of ,antarctica4 ,the facts as to the parasites seem also to prove that while the land connection existed there was a sea across ,south ,america in equatorial latitudes4 ,the parasite infests not only the frogs but the ,american toads known as ,bufo4 ,now ,bufo originated north of the equator in ,america and differs from the frogs which originated in southern ,south ,america in not being found in ,australia4 ,this raises the question of how the frogs could go to ,australia via ,antarctica carrying the parasite with them1 while the toads could not go4 ,metcalf's answer is that the toads were cut off from the southern part of ,south ,america by an equatorial sea until after the ,antarctic connection between the ,old ,world and the ,new was severed4 ,as ,patagonia let go of ,antarctica by subsidence of the intervening land area1 there was a probable concomitant rise of land through what is now middle ,south ,america and the northern and southern portions of this continent came together4#hg ,these various changes in the earth's crust have given rise to certain specific types of distribution of the lands1 which will now be considered4 ,we shall inquire what climatic conditions would arise from changes in 7a7 the continuity of the lands from north to south1 7b7 the amount of land in tropical latitudes1 and 7c7 the amount of land in middle and high latitudes4 7a7 ,at present the westward drift of warm waters1 set in motion by the trade winds1 is interrupted by land masses and turned poleward1 producing the important ,gulf ,stream ,drift and ,japan ,current in the northern hemisphere1 and corresponding1 though less important1 currents in the southern hemisphere4 ,during the past1 quite different sets of ocean currents doubtless have existed in response to a different distribution of land4 ,repeatedly1 in the mid-,cretaceous 7,fig4 #i7 and several other periods1 the present ,american barrier to the westward moving tropical current was broken in ,central ,america4 ,even if the supposed continent of ,gondwana ,land extended from ,africa to ,south ,america in equatorial latitudes1 strong currents must still have flowed westward along its northern shore under the impulse of the peculiarly strong trade winds which the equatorial land would create4 ,nevertheless at such times relatively little warm tropical water presumably entered the ,north ,atlantic1 for it escaped into the ,pacific4 ,at several other times1 such as the late ,ordovician and mid-,devonian1 when the isthmian barrier existed1 it probably turned an important current northward into what is now the ,mississippi ,basin instead of into the ,atlantic4 ,there it traversed an epeiric1 or mid-continental sea open to both north and south4 ,hence its effectiveness in warming ,arctic regions must have been quite different from that of the present ,gulf ,stream4 7b7 ,we will next consider the influences of changes in the amount of equatorial and tropical land4 ,as such lands are much hotter than the corresponding seas1 the intensity and width of the equatorial belt of low pressure must be great when they are extensive4 ,hence the trade winds must have been stronger than now whenever tropical lands were more extensive than at present4 ,this is because the trades are produced by the convection due to excessive heat along the heat equator4 ,there the air expands upward and flows poleward at high altitudes4 ,the trade wind consists of air moving toward the heat equator to take the place of the air which there rises4 ,when the lands in low latitudes were wide the trade winds must also have dominated a wide belt4 ,the greater width of the trade-wind belt today over ,africa than over the ,atlantic illustrates the matter4 ,the belt must have been still wider when ,gondwana ,land was large1 as it is believed to have been during the ,paleozoic era and the early ,mesozoic4 ,an increase in the width of the equatorial belt of low pressure under the influence of broad tropical lands would be accompanied not only by stronger and more widespread trade winds1 but by a corresponding strengthening of the subtropical belts of high pressure4 ,the chief reason would be the greater expansion of the air in the equatorial low pressure belt and the consequent more abundant outflow of air at high altitudes in the form of anti-trades or winds returning poleward above the trades4 ,such winds would pile up the air in the region of the high-pressure belt4 ,moreover1 since the meridians converge as one proceeds away from the equator1 the air of the poleward-moving anti-trades tends to be crowded as it reaches higher latitudes1 thus increasing the pressure4 ,unless there were a corresponding increase in tropical cyclones1 one of the most prominent results of the strengthened trades and the intensified subtropical high-pressure belt at times of broad lands in low latitudes would be great deserts4 ,it will be recalled that the trade-wind lowlands and the extra-tropical belt of highs are the great desert belts at present4 ,the trade-wind lowlands are desert because air moving into warmer latitudes takes up water except where it is cooled by rising on mountain-sides4 ,the belt of highs is arid because there1 too1 air is being warmed1 but in this case by descending from aloft4 ,again1 if the atmospheric pressure in the subtropical belt should be intensified1 the winds flowing poleward from this belt would necessarily become stronger4 ,these would begin as southwesterlies in the northern hemisphere and northwesterlies in the southern4 ,in the preceding chapter we have seen that such winds1 especially when cyclonic storms are few and mild1 are a powerful agent in transferring subtropical heat poleward4 ,if the strength of the westerlies were increased because of broad lands in low latitudes1 their efficacy in transferring heat would be correspondingly augmented4 ,it is thus evident that any change in the extent of tropical lands during the geologic past must have had important climatic consequences in changing the velocity of the atmospheric circulation and in altering the transfer of heat from low latitudes to high4 ,when the equatorial and tropical lands were broad the winds and currents must have been strong1 much heat must have been carried away from low latitudes1 and the contrast between low and high latitudes must have been relatively slight4 ,as we have already remarked1 leading paleogeographers believe that changes in the extent of the lands have been especially marked in low latitudes1 and that on the average there has been a decrease in the extent of land within the tropics4 ,gondwana ,land is the greatest illustration of this4 ,in the same way1 on the numerous paleogeographic maps of ,north ,america1 most paleogeographers have shown fairly extensive lands south of the latitude of the ,united ,states during most of the geologic epochs4#hh 7c7 ,there is evidence that during geologic history the area of the lands in middle and high latitudes1 as well as in low latitudes1 has changed radically4 ,an increase in such lands would cause the winters to grow colder4 ,this would be partly because of the loss of heat by radiation into the cold dry air over the continents in winter1 and partly because of increased reflection from snow and frost1 which gather much more widely upon the land than upon the ocean4 ,furthermore1 in winter when the continents are relatively cold1 there is a strong tendency for winds to blow out from the continent toward the ocean4 ,the larger the land the stronger this tendency4 ,in ,asia it gives rise to strong winter monsoons4 ,the effect of such winds is illustrated by the way in which the westerlies prevent the ,gulf ,stream from warming the eastern ,united ,states in winter4 ,the ,gulf ,stream warms northwestern ,europe much more than the ,united ,states because1 in ,europe1 the prevailing winds are onshore4 ,another effect of an increase in the area of the lands in middle and high latitudes would be to interpose barriers to oceanic circulation and thus lower the temperature of polar regions4 ,this would not mean glaciation in high latitudes1 however1 even when the lands were widespread as in the ,mesozoic and early ,tertiary4 ,students of glaciology are more and more thoroughly convinced that glaciation depends on the availability of moisture even more than upon low temperature4 ,in conclusion it may be noted that each of the several climatic influences of increased land area in the high latitudes would tend to increase the contrasts between land and sea1 between winter and summer1 and between low latitudes and high4 ,in other words1 so far as the effect upon high latitudes themselves is concerned1 an expansion of the lands there would tend in the same direction as a diminution in low latitudes4 ,in so far as the general trend of geological evolution has been toward more land in high latitudes and less in low1 it would help to produce a progressive increase in climatic diversity such as is faintly indicated in the rock strata4 ,on the other hand1 the oscillations in the distribution of the lands1 of which geology affords so much evidence1 must certainly have played an important part in producing the periodic changes of climate which the earth has undergone4 ,,iii4 ,throughout geological history there is abundant evidence that the process of contraction has led to marked differences not only in the distribution and area of the lands1 but in their height4 ,on the whole the lands have presumably increased in height since the ,proterozoic1 somewhat in proportion to the increased differentiation of continents and oceans4#hi ,if there has been such an increase1 the contrast between the climate of ocean and land must have been accentuated1 for highlands have a greater diurnal and seasonal range of temperature than do lowlands4 ,the ocean has very little range of either sort4 ,the large range at high altitudes is due chiefly to the small quantity of water vapor1 for this declines steadily with increased altitude4 ,a diminution in the density of the other constituents of the air also decreases the blanketing effect of the atmosphere4 ,in conformity with the great seasonal range in temperature at times when the lands stand high1 the direction of the wind would be altered4 ,when the lands are notably warmer than the oceans1 the winds commonly flow from land to sea1 and when the continents are much colder than the oceans1 the direction is reversed4 ,the monsoons of ,asia are examples4 ,strong seasonal winds disturb the normal planetary circulation of the trade winds in low latitudes and of the westerlies in middle latitudes4 ,they also interfere with the ocean currents set in motion by the planetary winds4 ,the net result is to hinder the transfer of heat from low latitudes to high1 and thus to increase the contrasts between the zones4 ,local as well as zonal contrasts are also intensified4 ,the higher the land1 the greater1 relatively speaking1 are the cloudiness and precipitation on seaward slopes1 and the drier the interior4 ,indeed1 most highlands are arid4 ,henry's#ij recent study of the vertical distribution of rainfall on mountain-sides indicates that a decrease sets in at about #cejj feet in the tropics and only a little higher in mid-latitudes4 ,in addition to the main effects upon atmospheric circulation and precipitation1 each of the many upheavals of the lands must have been accompanied by many minor conditions which tended toward diversity4 ,for example1 the streams were rejuvenated1 and instead of meandering perhaps over vast flood plains they intrenched their channels and in many cases dug deep gorges4 ,the water table was lowered1 soil was removed from considerable areas1 the bare rock was exposed1 and the type of dominant vegetation altered in many places4 ,an almost barren ridge may represent all that remains of what was once a vast forested flood plain4 ,thus1 increased elevation of the land produces contrasted conditions of slope1 vegetation1 availability of ground water1 exposure to wind and so forth1 and these unite in diversifying climate4 ,where mountains are formed1 strong contrasts are sure to occur4 ,the windward slopes may be very rainy1 while neighboring leeward slopes are parched by a dry foehn wind4 ,at the same time the tops may be snow-covered4 ,increased local contrasts in climatic conditions are known to influence the intensity of cyclonic storms1#ia and these affect the climatic conditions of all middle and high latitudes1 if not of the entire earth4 ,the paths followed by cyclonic storms are also altered by increased contrast between land and water4 ,when the continents are notably colder than the neighboring oceans1 high atmospheric pressure develops on the lands and interferes with the passage of lows1 which are therefore either deflected around the continent or forced to move slowly4 ,the distribution of lofty mountains has an even more striking climatic effect than the general uplift of a region4 ,in ,proterozoic times there was a great range in the ,lake ,superior region2 in the late ,devonian the ,acadian mountains of ,new ,england and the ,maritime ,provinces of ,canada possibly attained a height equal to the present ,rockies4 ,subsequently1 in the late ,paleozoic a significant range stood where the ,ouachitas now are4 ,accompanying the uplift of each of these ranges1 and all others1 the climate of the surrounding area1 especially to leeward1 must have been altered greatly4 ,many extensive salt deposits found now in fairly humid regions1 for example1 the ,pennsylvanian and ,permian deposits of ,kansas and ,oklahoma1 were probably laid down in times of local aridity due to the cutting off of moisture-bearing winds by the mountains of ,llanoria in ,louisiana and ,texas4 ,hence such deposits do not necessarily indicate periods of widespread and profound aridity4 ,when the causes of ancient glaciation were first considered by geologists1 about the middle of the nineteenth century1 it was usually assumed that the glaciated areas had been elevated to great heights1 and thus rendered cold enough to permit the accumulation of glaciers4 ,the many glaciers occurring in the ,alps of central ,europe where glaciology arose doubtless suggested this explanation4 ,however1 it is now known that most of the ancient glaciation was not of the alpine type1 and there is adequate proof that the glacial periods cannot be explained as due directly and solely to uplift4 ,nevertheless1 upheavals of the lands are among the most important factors in controlling climate1 and variations in the height of the lands have doubtless assisted in producing climate oscillations1 especially those of long duration4 ,moreover1 the progressive increase in the height of the lands has presumably played a part in fostering local and zonal diversity in contrast with the relative uniformity of earlier geological times4 ,,iv4 ,the contraction of the earth has been accompanied by volcanic activity as well as by changes in the extent1 distribution1 and altitude of the lands4 ,the probable part played by volcanic dust as a contributory factor in producing short sudden climatic variations has already been discussed4 ,there is1 however1 another though probably less important respect in which volcanic activity may have had at least a slight climatic significance4 ,the oldest known rocks1 those of the ,archean era1 contain so much igneous matter that many students have assumed that they show that the entire earth was once liquid4 ,it is now considered that they merely indicate igneous activity of great magnitude4 ,in the later part of ,proterozoic time1 during the second quarter of the earth's history according to ,schuchert's estimate1 there were again vast outflowings of lava4 ,in the ,lake ,superior district1 for example1 a thickness of more than a mile accumulated over a large area1 and lavas are common in many areas where rocks of this age are known4 ,the next quarter of the earth's history elapsed without any correspondingly great outflows so far as is known1 though several lesser ones occurred4 ,toward the end of the last quarter1 and hence quite recently from the geological standpoint1 another period of outflows1 perhaps as noteworthy as that of the ,proterozoic1 occurred in the ,cretaceous and ,tertiary4 ,the climatic effects of such extensive lava flows would be essentially as follows3 ,in the first place so long as the lavas were hot they would set up a local system of convection with inflowing winds4 ,this would interfere at least a little with the general winds of the area4 ,again1 where the lava flowed out into water1 or where rain fell upon hot lava1 there would be rapid evaporation which would increase the rainfall4 ,then after the lava had cooled1 it would still influence climate a trifle in so far as its color was notably darker or lighter than that of the average surface4 ,dark surfaces absorb solar heat and become relatively warm when the sun shines upon them4 ,dark objects likewise radiate heat more rapidly than light-colored objects4 ,hence they cool more rapidly at night1 and in the winter4 ,as most lavas are relatively dark they increase the average diurnal range of temperature4 ,hence even after they are cool they increase the climatic diversity of the land4 ,the amount of heat given to the atmosphere by an extensive lava flow1 though large according to human standards1 is small compared with the amount received from the sun by a like area1 except during the first few weeks or months before the lava has formed a thick crust4 ,furthermore1 probably only a small fraction of any large series of flows occurred in a given century or millennium4 ,moreover1 even the largest lava flows covered an area of only a few hundredths of one per cent of the earth's surface4 ,nevertheless1 the conditions which modify climate are so complicated that it would be rash to state that this amount of additional heat has been of no climatic significance4 ,like the proverbial straw that broke the camel's back1 the changes it would surely produce in local convection1 atmospheric pressure1 and the direction of the wind may have helped to shift the paths of storms and to produce other complications which were of appreciable climatic significance4 ,v4 ,the last point which we shall consider in connection with the effect of the earth's interior upon climate is internal heat4 ,the heat given off by lavas is merely a small part of that which is emitted by the earth as a whole4 ,in the earliest part of geological history enough heat may have escaped from the interior of the earth to exert a profound influence on the climate4 ,knowlton1#ib as we have seen1 has recently built up an elaborate theory on this assumption4 ,at present1 however1 accurate measurements show that the escape of heat is so slight that it has no appreciable influence except in a few volcanic areas4 ,it is estimated to raise the average temperature of the earth's surface less than #j4a deg4,c4#ic ,in order to contribute enough heat to raise the surface temperature #a deg4,c41 the temperature gradient from the interior of the earth to the surface would need to be ten times as great as now1 for the rate of conduction varies directly with the gradient4 ,if the gradient were ten times as great as now1 the rocks at a depth of two and one-half miles would be so hot as to be almost liquid according to ,barrell's#id estimates4 ,the thick strata of unmetamorphosed ,paleozoic rocks indicate that such high temperatures have not prevailed at such slight depths since the ,proterozoic4 ,furthermore1 the fact that the climate was cold enough to permit glaciation early in the ,proterozoic era and at from one to three other times before the opening of the ,paleozoic suggests that the rate of escape of heat was not rapid even in the first half of the earth's recorded history4 ,yet even if the general escape of heat has never been large since the beginning of the better-known part of geological history1 it was presumably greater in early times than at present4 ,if there actually has been an appreciable decrease in the amount of heat given out by the earth's interior1 its effects would agree with the observed conditions of the geological record4 ,it would help to explain the relative mildness of zonal1 seasonal1 and local contrasts of climate in early geological times1 but it would not help to explain the long oscillations from era to era which appear to have been of much greater importance4 ,those oscillations1 so far as we can yet judge1 may have been due in part to solar changes1 but in large measure they seem to be explained by variations in the extent1 distribution1 and altitude of the lands4 ,such variations appear to be the inevitable result of the earth's contraction4 ,,footnotes3 ,footnote #gj3 ,chas4 ,schuchert3 ,the ,earth's ,changing ,surface and ,climate during ,geologic ,time2 in ,lull3 ,the ,evolution of the ,earth and ,its ,inhabitants1 #aiah1 p4 #ee4 ,footnote #ga3 ,quoted by ,j4 ,cornet3 ,cours de ,geologie1 #aibj1 p4 #ccj4 ,footnote #gb3 ,t4 ,c4 ,chamberlin3 ,the ,order of ,magnitude of the ,shrinkage of the ,earth2 ,jour4 ,geol41 ,vol4 #bh1 #aibj1 pp4 #a-ag1 #abf-aeg4 ,footnote #gc3 ,g4 ,i4 ,taylor3 ,philosophical ,transactions1 ,a4 #bbj1 #aiai1 pp4 #a-cc2 ,monthly ,notices ,royal ,astron4 ,soc41 ,jan41 #aibj1 ,vol4 #hj1 p4 #cjh4 ,footnote #gd3 ,j4 ,jeffreys3 ,monthly ,notices ,royal ,astron4 ,soc41 ,jan41 #aibj1 ,vol4 #hj1 p4 #cji4 ,footnote #ge3 ,e4 ,w4 ,brown3 personal communication4 ,footnote #gf3 ,c4 ,s4 ,slichter3 ,the ,rotational ,period of a ,heterogeneous ,spheroid2 in ,contributions to the ,fundamental ,problems of ,geology1 by ,t4 ,c4 ,chamberlin1 et al41 ,carnegie ,inst4 of ,wash41 ,no4 #ajg1 #aiji4 ,footnote #gg3 ,e4 ,suess3 ,the ,face of the ,earth1 ,vol4 ,,ii1 p4 #eec1 #aija4 ,footnote #gh3 ,chas4 ,schuchert3 ,the ,earth's ,changing ,surface and ,climate2 in ,lull3 ,the ,evolution of the ,earth and ,its ,inhabitants1 #aiah1 p4 #gh4 ,footnote #gi3 ,j4 ,barren3 ,rhythms and the ,measurement of ,geologic ,time2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #bh1 #aiag1 p4 #hch4 ,footnote #hj3 ,chas4 ,schuchert3 loc4 cit41 p4 #gh4 ,footnote #ha3 ,t4 ,c4 ,chamberlin3 ,diastrophism1 the ,ultimate ,basis of ,correlation2 ,jour4 ,geol41 ,vol4 #af1 #aiji2 ,chas4 ,schuchert3 loc4 cit4 ,footnote #hb3 ,pirsson-,schuchert3 ,textbook of ,geology1 #aiae1 ,vol4 ,,ii1 p4 #ihb2 ,chas4 ,schuchert3 ,paleogeography of ,north ,america2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #bj1 pp4 #dbg-fjf2 reference on p4 #dii4 ,footnote #hc3 ,the general subject of the climatic significance of continentality is discussed by ,c4 ,e4 ,p4 ,brooks3 continentality and ,temperature2 ,quart4 ,jour4 ,royal ,meteorol4 ,soc41 ,april1 #aiag1 and ,oct41 #aiah4 ,footnote #hd3 ,chas4 ,schuchert3 ,climates of ,geologic ,time2 in ,the ,climatic ,factor2 ,carnegie ,institution1 #aiad1 p4 #bhf4 ,footnote #he3 ,a4 de ,lapparent3 ,traite de ,geologie1 #aijf4 ,footnote #hf3 ,chas4 ,schuchert3 ,historical ,geology1 #aiae1 p4 #dfd4 ,footnote #hg3 ,m4 ,m4 ,metcalf3 ,upon an important method of studying problems of relationship and of geographical distribution2 ,proceedings ,national ,academy of ,sciences1 ,vol4 #f1 ,july1 #aibj1 pp4 #dcb-dcc4 ,footnote #hh3 ,chas4 ,schuchert3 ,paleogeography of ,north ,america2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #bj1 #aiaj2 and ,willis1 ,salisbury1 and others3 ,outlines of ,geologic ,history1 #aiaj4 ,footnote #hi3 ,chas4 ,schuchert3 ,the ,earth's ,changing ,surface and ,climate2 in ,lull3 ,the ,evolution of the ,earth and ,its ,inhabitants1 #aiah1 p4 #ej4 ,footnote #ij3 ,a4 ,j4 ,henry3 ,the ,decrease of ,precipitation with ,altitude2 ,monthly ,weather ,review1 ,vol4 #dg1 #aiai1 pp4 #cc-da4 ,footnote #ia3 ,chas4 ,f4 ,brooks3 ,monthly ,weather ,review1 ,vol4 #df1 #aiah1 p4 #eaa2 and also ,a4 ,j4 ,henry and others3 ,weather ,forecasting in the ,united ,states1 #aiac4 ,footnote #ib3 ,f4 ,h4 ,knowlton3 ,evolution of ,geologic ,climates2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #cj1 ,dec41 #aiai1 pp4 #dii-eff4 ,footnote #ic3 ,talbert1 quoted by ,i4 ,bowman3 ,forest ,physiography1 #aiaa1 p4 #fc4 ,footnote #id3 ,j4 ,barrell3 ,rhythms and the ,measurement of ,geologic ,time2 ,bull4 ,geol4 ,soc4 ,am41 ,vol4 #bh1 #aiag1 pp4 #gde-ijd4 ,,chapter ,,xii ,,post-,,glacial ,,crustal ,,movements ,,and ,,climatic ,,changes ,an interesting practical application of some of the preceding generalizations is found in an attempt by ,c4 ,e4 ,p4 ,brooks#ie to interpret post-glacial climatic changes almost entirely in terms of crustal movement4 ,we believe that he carries the matter much too far1 but his discussion is worthy of rather full recapitulation1 not only for its theoretical value but because it gives a good summary of post-glacial changes4 ,his climatic table for northwest ,europe as reprinted from the annual report of the ,smithsonian ,institution for #aiag1 p4 #cff1 is as follows3 ,phase ,climate ,date #a4 ,the ,last ,great ,arctic climate4 #cj1jjj-ah1jjj ,b4 ,c4 ,glaciation4 #b4 ,the ,retreat of the ,severe continental #ah1jjj-fjjj ,b4 ,c4 ,glaciers4 climate4 #c4 ,the ,continental ,phase4 ,continental climate4 #fjjj-djjj ,b4 ,c4 #d4 ,the ,maritime ,phase4 ,warm and moist4 #djjj-cjjj ,b4 ,c4 #e4 ,the ,later ,forest ,phase4 ,warm and dry4 #cjjj-ahjj ,b4 ,c4 #f4 ,the ,peat-,bog ,phase4 ,cooler and moister4 #ahjj ,b4 ,c4-#cjj ,a4 ,d4 #g4 ,the ,recent ,phase4 ,becoming drier4 #cjj ,a4 ,d4- ,brooks bases his chronology largely on ,de ,geer's measurements of the annual layers of clay in lake bottoms but makes much use of other evidence4 ,according to ,brooks the last glacial epoch lasted roughly from #cj1jjj to #ah1jjj ,b4 ,c41 but this includes a slight amelioration of climate followed by a readvance of the ice1 known as the ,buhl stage4 ,during the time of maximum glaciation the ,british ,isles stood twenty or thirty feet higher than now and ,scandinavia was considerably more elevated4 ,the author believes that this caused a fall of #a deg4,c4 in the temperature of the ,british ,isles and of #b deg4,c4 in ,scandinavia4 ,by an ingenious though not wholly convincing method of calculation he concludes that this lowering of temperature1 aided by an increase in the area of the lands1 sufficed to start an ice sheet in ,scandinavia4 ,the relatively small area of ice cooled the air and gave rise to an area of high barometric pressure4 ,this in turn is supposed to have caused further expansion of the ice and to have led to full-fledged glaciation4 ,about #ah1jjj ,b4 ,c4 the retreat of the ice began in good earnest4 ,even though no evidence has yet been found1 ,brooks believes there must have been a change in the distribution of land and sea to account for the diminution of the ice4 ,the ensuing millenniums formed the ,magdalenian period in human history1 the last stage of the ,paleolithic1 when man lived in caves and reindeer were abundant in central ,europe4#if ,at first the ice retreated very slowly and there were periods when for scores of years the ice edge remained stationary or even readvanced4 ,about #aj1jjj ,b4 ,c4 the edge of the ice lay along the southern coast of ,sweden4 ,during the next #bjjj years it withdrew more rapidly to about #ei deg4,n4 ,then came the ,fennoscandian pause1 or ,gschnitz stage1 when for about #bjj years the ice edge remained in one position1 forming a great moraine4 ,brooks suggests that this pause about #hjjj ,b4 ,c4 was due to the closing of the connection between the ,atlantic ,ocean and the ,baltic ,sea and the synchronous opening of a connection between the ,baltic and the ,white ,seas1 whereby cold ,arctic waters replaced the warmer ,atlantic waters4 ,he notes1 however1 that about #gejj ,b4 ,c4 the obliquity of the ecliptic was probably nearly #a deg4 greater than at present4 ,this he calculates to have caused the climate of ,germany and ,sweden to be #a deg4,f4 colder than at present in winter and #a deg4,f4 warmer in summer4 ,the next climatic stage was marked by a rise of temperature till about #fjjj ,b4 ,c4 ,during this period the ice at first retreated1 presumably because the climate was ameliorating1 although no cause of such amelioration is assigned4 ,at length the ice lay far enough north to allow a connection between the ,baltic and the ,atlantic by way of ,lakes ,wener and ,wetter in southern ,sweden4 ,this is supposed to have warmed the ,baltic ,sea and to have caused the climate to become distinctly milder4 ,next the land rose once more so that the ,baltic was separated from the ,atlantic and was converted into the ,ancylus lake of fresh water4 ,the southwest ,baltic region then stood #djj feet higher than now4 ,the result was the ,daun stage1 about #ejjj ,b4 ,c41 when the ice halted or perhaps readvanced a little1 its front being then near ,ragunda in about latitude #fc deg44 ,why such an elevation did not cause renewed glaciation instead of merely the slight ,daun pause1 ,brooks does not explain1 although his calculations as to the effect of a slight elevation of the land during the main period of glaciation from #cj1jjj to #ah1jjj ,b4 ,c4 would seem to demand a marked readvance4 ,after #ejjj ,b4 ,c4 there ensued a period when the climate1 although still distinctly continental1 was relatively mild4 ,the winters1 to be sure1 were still cold but the summers were increasingly warm4 ,in ,sweden1 for example1 the types of vegetation indicate that the summer temperature was #g deg4,f4 higher than now4 ,storms1 ,brooks assumes1 were comparatively rare except on the outer fringe of ,great ,britain4 ,there they were sufficiently abundant so that in the ,northwest they gave rise to the first ,peat-,bog period1 during which swamps replaced forests of birch and pine4 ,southern and eastern ,england1 however1 probably had a dry continental climate4 ,even in northwest ,norway storms were rare as is indicated by remains of forests on islands now barren because of the strong winds and fierce storms4 ,farther east most parts of central and northern ,europe were relatively dry4 ,this was the early ,neolithic period when man advanced from the use of unpolished to polished stone implements4 ,not far from #djjj ,b4 ,c4 the period of continental climate was replaced by a comparatively moist maritime climate4 ,brooks believes that this was because submergence opened the mouth of the ,baltic and caused the fresh ,ancylus lake to give place to the so-called ,litorina sea4 ,the temperature in ,sweden averaged about #c deg4,f4 higher than at present and in southwestern ,norway #b deg44 ,more important than this was the small annual range of temperature due to the fact that the summers were cool while the winters were mild4 ,because of the presence of a large expanse of water in the ,baltic region1 storms1 as our author states1 then crossed ,great ,britain and followed the ,baltic depression1 carrying the moisture far inland4 ,in spite of the additional moisture thus available the snow line in southern ,norway was higher than now4 ,at this point ,brooks turns to other parts of the world4 ,he states that not far from #djjj ,b4 ,c41 a submergence of the lands1 rarely amounting to more than twenty-five feet1 took place not only in the ,baltic region but in ,ireland1 ,iceland1 ,spitzbergen1 and other parts of the ,arctic ,ocean1 as well as in the ,white ,sea1 ,greenland1 and the eastern part of ,north ,america4 ,evidences of a mild climate are found in all those places4 ,similar evidence of a mild warm climate is found in ,east ,africa1 ,east ,australia1 ,tierra del ,fuego1 and ,antarctica4 ,the dates are not established with certainty but they at least fall in the period immediately preceding the present epoch4 ,in explanation of these conditions ,brooks assumes a universal change of sea level4 ,he suggests with some hesitation that this may have been due to one of ,pettersson's periods of maximum tide-generating force4 ,according to ,pettersson the varying positions of the moon1 earth1 and sun cause the tides to vary in cycles of about #i1 #ij1 and #ahjj years1 though the length of the periods is not constant4 ,when tides are high there is great movement of ocean waters and hence a great mixture of the water at different latitudes4 ,this is supposed to cause an amelioration of climate4 ,the periods of maximum and minimum tide-generating force are as follows3 ,maxima #cejj ,b4 ,c4--------#bajj ,b4 ,c4--------#cej ,b4 ,c4-------,a4 ,d4 #adcd ,minima ---------#bhjj ,b4 ,c4--------#abjj ,b4 ,c4-------,a4 ,d4 #ecj--------- ,brooks thinks that the big trees in ,california and the ,norse sagas and ,germanic myths indicate a rough agreement of climatic phenomena with ,pettersson's last three dates1 while the mild climate of #djjj ,b4 ,c4 may really belong to #cejj ,b4 ,c4 ,he gives no evidence confirming ,pettersson's view at the other three dates4 ,to return to ,brooks' sketch of the relation of climatic pulsations to the altitude of the lands1 by #cjjj ,b4 ,c41 that is1 toward the close of the ,neolithic period1 further elevation is supposed to have taken place over the central latitudes of western ,europe4 ,southern ,britain1 which had remained constantly above its present level ever since #cj1jjj ,b4 ,c41 was perhaps ninety feet higher than now4 ,ireland was somewhat enlarged by elevation1 the ,straits of ,dover were almost closed1 and parts of the present ,north ,sea were land4 ,to these conditions ,brooks ascribes the prevalence of a dry continental climate4 ,the storms shifted northward once more1 the winds were mild1 as seems to be proved by remains of trees in exposed places2 and forests replaced fields of peat and heath in ,britain and ,germany4 ,the summers were perhaps warmer than now but the winters were severe4 ,the relatively dry climate prevailed as far west as ,ireland4 ,for example1 in ,drumkelin ,bog in ,donegal ,county a corded oak road and a two-story log cabin appear to belong to this time4 ,fourteen feet of bog lie below the floor and twenty-six above4 ,this period1 perhaps #cjjj-bjjj ,b4 ,c41 was the legendary heroic age of ,ireland when the vigour of the ,irish reached a level not since attained4 ,this1 as ,brooks points out1 may have been a result of the relatively dry climate1 for today the extreme moisture of ,ireland seems to be a distinct handicap4 ,in ,scandinavia1 civilization1 or at least the stage of relative progress1 was also high at this time4 ,by #afjj ,b4 ,c4 the land had assumed nearly its present level in the ,british ,isles and the southern ,baltic region1 while northern ,scandinavia still stood lower than now4 ,the climate of ,britain and ,germany was so humid that there was an extensive formation of peat even on high ground not before covered4 ,this moist stage seems to have lasted almost to the time of ,christ1 and may have been the reason why the ,romans described ,britain as peculiarly wet and damp4 ,at this point ,brooks again departs from northwest ,europe to a wider field3 ,it is possible that we have to attribute this damp period in ,northwest ,europe to some more general cause1 for ,ellsworth ,huntington's curves of tree-growth in ,california and climate in ,western ,asia both show moister conditions from about #ajjj ,b4 ,c4 to ,a4 ,d4 #bjj1 and the same author believes that the ,mediterranean lands had a heavier rainfall about #ejj ,b4 ,c4 to ,a4 ,d4 #bjj4 ,it seems that the phase was marked by a general increase of the storminess of the temperate regions of the northern hemisphere at least1 with a maximum between ,ireland and ,north ,germany1 indicating probably that the ,baltic again became the favourite track of depressions from the ,atlantic4 ,brooks ends his paper with a brief resume of glacial changes in ,north ,america1 but as the means of dating events are unreliable the degree of synchronism with ,europe is not clear4 ,he sums up his conclusions as follows3 ,on the whole it appears that though there is a general similarity in the climatic history of the two sides of the ,north ,atlantic1 the changes are not really contemporaneous1 and such relationship as appears is due mainly to the natural similarity in the geographical history of two regions both recovering from an ,ice ,age1 and only very partially to world-wide pulsations of climate4 ,additional evidence on this head will be available when ,baron de ,geer publishes the results of his recent investigations of the seasonal glacial clays of ,north ,america1 especially if1 as he hopes1 he is able to correlate the banding of these clays with the growth-rings of the big trees4 ,when we turn to the northwest of ,north ,america1 this is brought out very markedly4 ,for in ,yukon and ,alaska the ,ice ,age was a very mild affair compared with its severity in eastern ,america and ,scandinavia4 ,as the land had not a heavy ice-load to recover from1 there were no complicated geographical changes4 ,also1 there were no fluctuations of climate1 but simply a gradual passage to present conditions4 ,the latter circumstance especially seems to show that the emphasis laid on geographical rather than astronomical factors of great climatic changes is not misplaced4 ,brooks' painstaking discussion of post-glacial climatic changes is of great value because of the large body of material which he has so carefully wrought together4 ,his strong belief in the importance of changes in the level of the lands deserves serious consideration4 ,it is difficult1 however1 to accept his final conclusion that such changes are the main factors in recent climatic changes4 ,it is almost impossible1 for example1 to believe that movements of the land could produce almost the same series of climatic changes in ,europe1 ,central ,asia1 the western and eastern parts of ,north ,america1 and the southern hemisphere4 ,yet such changes appear to have occurred during and since the glacial period4 ,again there is no evidence whatever that movements of the land have anything to do with the historic cycles of climate or with the cycles of weather in our own day1 which seem to be the same as glacial cycles on a small scale4 ,also1 as ,dr4 ,simpson points out in discussing ,brooks' paper1 there appears no solution along these lines of the problem connected with rich vegetation in both polar circles and the ice-age which produced the ice-sheet at sea-level in ,northern ,india4 ,nevertheless1 we may well believe that ,brooks is right in holding that changes in the relative level and relative area of land and sea have had important local effects4 ,while they are only one of the factors involved in climatic changes1 they are certainly one that must constantly be kept in mind4 ,,footnotes3 ,footnote #ie3 ,c4 ,e4 ,p4 ,brooks3 ,the ,evolution of ,climate in ,northwest ,europe4 ,quart4 ,jour4 ,royal ,meteorol4 ,soc41 ,vol4 #dg1 #aiba1 pp4 #agc-aid4 ,footnote #if3 ,h4 ,f4 ,osborn3 ,men of the ,old ,stone ,age1 ,n4 ,y41 #aiae2 ,j4 ,m4 ,tyler3 ,the ,new ,stone ,age in ,northwestern ,europe1 ,n4 ,y41 #aibj4 ,,chapter ,,xiii ,,the ,,changing ,,composition ,,of ,,oceans ,,and ,,atmosphere ,having discussed the climatic effect of movements of the earth's crust during the course of geological time1 we are now ready to consider the corresponding effects due to changes in the movable envelopes--the oceans and the atmosphere4 ,variations in the composition of sea water and of air and in the amount of air must almost certainly have occurred1 and must have produced at least slight climatic consequences4 ,it should be pointed out at once that such variations appear to be far less important climatically than do movements of the earth's crust and changes in the activity of the sun4 ,moreover1 in most cases1 they are not reversible as are the crustal and solar phenomena4 ,hence1 while most of them appear to have been unimportant so far as climatic oscillations and fluctuations are concerned1 they seemingly have aided in producing the slight secular progression to which we have so often referred4 ,there is general agreement among geologists that the ocean has become increasingly saline throughout the ages4 ,indeed1 calculations of the rate of accumulation of salt have been a favorite method of arriving at estimates of the age of the ocean1 and hence of the earliest marine sediments4 ,so far as known1 however1 no geologist or climatologist has discussed the probable climatic effects of increased salinity4 ,yet it seems clear that an increase in salinity must have a slight effect upon climate4 ,salinity affects climate in four ways3 7#a7 ,it appreciably influences the rate of evaporation2 7#b7 it alters the freezing point2 7#c7 it produces certain indirect effects through changes in the absorption of carbon dioxide2 and 7#d7 it has an effect on oceanic circulation4 7#a7 ,according to the experiments of ,mazelle and ,okada1 as reported by ,kruemmel1#ig evaporation from ordinary sea water is from #i to #cj per cent less rapid than from fresh water under similar conditions4 ,the variation from #i to #cj per cent found in the experiments depends1 perhaps1 upon the wind velocity4 ,when salt water is stagnant1 rapid evaporation tends to result in the development of a film of salt on the top of the water1 especially where it is sheltered from the wind4 ,such a film necessarily reduces evaporation4 ,hence the relatively low salinity of the oceans in the past probably had a tendency to increase the amount of water vapor in the air4 ,even a little water vapor augments slightly the blanketing effect of the air and to that extent diminishes the diurnal and seasonal range of temperature and the contrast from zone to zone4 7#b7 ,increased salinity means a lower freezing temperature of the oceans and hence would have an effect during cold periods such as the present and the ,pleistocene ice age4 ,it would not1 however1 be of importance during the long warm periods which form most of geologic time4 ,a salinity of about #c4e per cent at present lowers the freezing point of the ocean roughly #b deg4,c4 below that of fresh water4 ,if the ocean were fresh and our winters as cold as now1 all the harbors of ,new ,england and the ,middle ,atlantic ,states would be icebound4 ,the ,baltic ,sea would also be frozen each winter1 and even the eastern harbors of the ,british ,isles would be frequently locked in ice4 ,at high latitudes the area of permanently frozen oceans would be much enlarged4 ,the effect of such a condition upon marine life in high latitudes would be like that of a change to a warmer climate4 ,it would protect the life on the continental shelf from the severe battering of winter storms4 ,it would also lessen the severity of the winter temperature in the water for when water freezes it gives up much latent heat1--eighty calories per cubic centimeter4 ,part of this raises the temperature of the underlying water4 ,the expansion of the ice near northern shores would influence the life of the lands quite differently from that of the oceans4 ,it would act like an addition of land to the continents and would1 therefore1 increase the atmospheric contrasts from zone to zone and from continental interior to ocean4 ,in summer the ice upon the sea would tend to keep the coastal lands cool1 very much as happens now near the ,arctic ,ocean1 where the ice floes have a great effect through their reflection of light and their absorption of heat in melting4 ,in winter the virtual enlargement of the continents by the addition of an ice fringe would decrease the snowfall upon the lands4 ,still more important would be the effect in intensifying the anti-cyclonic conditions which normally prevail in winter not only over continents but over ice-covered oceans4 ,hence the outblowing cold winds would he strengthened4#ih ,the net effect of all these conditions would apparently be a diminution of snowfall in high latitudes upon the lands even though the summer snowfall upon the ocean and the coasts may have increased4 ,this condition may have been one reason why widespread glaciation does not appear to have prevailed in high latitudes during the ,proterozoic and ,permian glaciations1 even though it occurred farther south4 ,if the ocean during those early glacial epochs were ice-covered down to middle latitudes1 a lack of extensive glaciation in high latitudes would be no more surprising than is the lack of ,pleistocene glaciation in the northern parts of ,alaska and ,asia4 ,great ice sheets are impossible without a large supply of moisture4 7#c7 ,among the indirect effects of salinity one of the chief appears to be that the low salinity of the water in the past and the greater ease with which it froze presumably allowed the temperature of the entire ocean to be slightly higher than now4 ,this is because ice serves as a blanket and hinders the radiation of heat from the underlying water4 ,the temperature of the ocean has a climatic significance not only directly1 but indirectly through its influence on the amount of carbon dioxide held by the oceans4 ,a change of even #a deg4,c4 from the present mean temperature of #b deg4,c4 would alter the ability of the entire ocean to absorb carbon dioxide by about #d per cent4 ,this1 according to ,f4 ,w4 ,clarke1#ii is because the oceans contain from eighteen to twenty-seven times as much carbon dioxide as the air when only the free carbon dioxide is considered1 and about seventy times as much according to ,johnson and ,williamson#ajj when the partially combined carbon dioxide is also considered4 ,moreover1 the capacity of water for carbon dioxide varies sharply with the temperature4#aja ,hence a rise in temperature of only #a deg4,c4 would theoretically cause the oceans to give up from #cj to #bhj times as much carbon dioxide as the air now holds4 ,this1 however1 is on the unfounded assumption that the oceans are completely saturated4 ,the important point is merely that a slight change in ocean temperature would cause a disproportionately large change in the amount of carbon dioxide in the air with all that this implies in respect to blanketing the earth1 and thus altering temperature4 7#d7 ,another and perhaps the most important effect of salinity upon climate depends upon the rapidity of the deep-sea circulation4 ,the circulation is induced by differences of temperature1 but its speed is affected at least slightly by salinity4 ,the vertical circulation is now dominated by cold water from subpolar latitudes4 ,except in closed seas like the ,mediterranean the lower portions of the ocean are near the freezing point4 ,this is because cold water sinks in high latitudes by reason of its superior density1 and then creeps to low latitudes4 ,there it finally rises and replaces either the water driven poleward by the winds1 or that which has evaporated from the ,surface4#ajb ,during past ages1 when the sea water was less salty1 the circulation was presumably more rapid than now4 ,this was because1 in tropical regions1 the rise of cold water is hindered by the sinking of warm surface water which is relatively dense because evaporation has removed part of the water and caused an accumulation of salt4 ,according to ,kruemmel and ,mill1#ajc the surface salinity of the subtropical belt of the ,north ,atlantic commonly exceeds #c4g per cent and sometimes reaches #c4gg per cent1 whereas the underlying waters have a salinity of less than #c4e per cent and locally as little as #c4dd per cent4 ,the other oceans are slightly less saline than the ,north ,atlantic at all depths1 but the vertical salinity gradients along the tropics are similar4 ,according to the ,smithsonian ,physical ,tables1 the difference in salinity between the surface water and that lying below is equivalent to a difference of 4#jjc in density1 where the density of fresh water is taken as #a4jjj4 ,since the decrease in density produced by warming water from the temperature of its greatest density 7#d deg4,c47 to the highest temperatures which ever prevail in the ocean 7#cj deg4,c4 or #hf deg4,f47 is only 4#jjd1 the more saline surface waters of the dry tropics are at most times almost as dense as the less saline but colder waters beneath the surface1 which have come from higher latitudes4 ,during days of especially great evaporation1 however1 the most saline portions of the surface waters in the dry tropics are denser than the underlying waters and therefore sink1 and produce a temporary local stagnation in the general circulation4 ,such a sinking of the warm surface waters is reported by ,kruemmel1 who detected it by means of the rise in temperature which it produces at considerable depths4 ,if such a hindrance to the circulation did not exist1 the velocity of the deep-sea movements would be greater4 ,if in earlier times a more rapid circulation occurred1 low latitudes must have been cooled more than now by the rise of cold waters4 ,at the same time higher latitudes were presumably warmed by a greater flow of warm water from tropical regions because less of the surface heat sank in low latitudes4 ,such conditions would tend to lessen the climatic contrast between the different latitudes4 ,hence1 in so far as the rate of deep-sea circulation depends upon salinity1 the slowly increasing amount of salt in the oceans must have tended to increase the contrasts between low and high latitudes4 ,thus for several reasons1 the increase of salinity during geologic history seems to deserve a place among the minor agencies which help to explain the apparent tendency toward a secular progression of climate in the direction of greater contrasts between tropical and subpolar latitudes4 ,changes in the composition and amount of the atmosphere have presumably had a climatic importance greater than that of changes in the salinity of the oceans4 ,the atmospheric changes may have been either progressive or cyclic1 or both4 ,in early times1 according to the nebular hypothesis1 the atmosphere was much more dense than now and contained a larger percentage of certain constituents1 notably carbon dioxide and water4 ,the planetesimal hypothesis1 on the other hand1 postulates an increase in the density of the atmosphere1 for according to this hypothesis the density of the atmosphere depends upon the power of the earth to hold gases1 and this power increases as the earth grows bigger with the infall of material from without4#ajd ,whichever hypothesis may be correct1 it seems probable that when life first appeared on the land the atmosphere resembled that of today in certain fundamental respects4 ,it contained the elements essential to life1 and its blanketing effect was such as to maintain temperatures not greatly different from those of the present4 ,the evidence of this depends largely upon the narrow limits of temperature within which the activities of modern life are possible1 and upon the cumulative evidence that ancient life was essentially similar to the types now living4 ,the resemblance between some of the oldest forms and those of today is striking4 ,for example1 according to ,professor ,schuchert3#aje ,many of the living genera of forest trees had their origin in the ,cretaceous1 and the giant sequoias of ,california go back to the ,triassic1 while ,ginkgo is known in the ,permian4 ,some of the fresh-water molluscs certainly were living in the early periods of the ,mesozoic1 and the lung-fish of today 7,ceratodus7 is known as far back as the ,triassic and is not very unlike other lung-fishes of the ,devonian4 ,the higher vertebrates and insects1 on the other hand1 are very sensitive to their environment1 and therefore do not extend back generically beyond the ,cenozoic1 and only in a few instances even as far as the ,oligocene4 ,of marine invertebrates the story is very different1 for it is well known that the horseshoe crab 7,limulus7 lived in the ,upper ,jurassic1 and ,nautilus in the ,triassic1 with forms in the ,devonian not far removed from this genus4 ,still longer-ranging genera occur among the brachiopods1 for living ,lingula and ,crania have specific representatives as far back as the early ,ordovician4 ,among living foraminifers1 ,lagena1 ,globigerina1 and ,nodosaria are known in the later ,cambrian or early ,ordovician4 ,in the ,middle ,cambrian near ,field1 ,british ,columbia1 ,walcott has found a most varied array of invertebrates among which are crustaceans not far removed from living forms4 ,zooelogists who see these wonderful fossils are at once struck with their modernity and the little change that has taken place in certain stocks since that far remote time4 ,back of the ,paleozoic1 little can be said of life from the generic standpoint1 since so few fossils have been recovered1 but what is at hand suggests that the marine environment was similar to that of today4 ,at present1 as we have repeatedly seen1 little growth takes place either among animals or plants at temperatures below #j deg4,c4 or above #dj deg4,c41 and for most species the limiting temperatures are about #aj deg4 and #cj deg44 ,the maintenance of so narrow a scale of temperature is a function of the atmosphere1 as well as of the sun4 ,without an atmosphere1 the temperature by day would mount fatally wherever the sun rides high in the sky4 ,by night it would fall everywhere to a temperature approaching absolute zero1 that is -#bgc deg4,c4 ,some such temperature prevails a few miles above the earth's surface1 beyond the effective atmosphere4 ,indeed1 even if the atmosphere were almost as it is now1 but only lacked one of the minor constituents1 a constituent which is often actually ignored in statements of the composition of the air1 life would be impossible4 ,tyndall concludes that if water vapor were entirely removed from the atmosphere for a single day and night1 all life--except that which is dormant in the form of seeds1 eggs1 or spores--would be exterminated4 ,part would be killed by the high temperature developed by day when the sun was high1 and part1 by the cold night4 ,the testimony of ancient glaciation as to the slight difference in the climate and therefore in the atmosphere of early and late geological times is almost as clear as that of life4 ,just as life proves that the earth can never have been extremely cold during hundreds of millions of years1 so glaciation in moderately low latitudes near the dawn of earth history and at several later times1 proves that the earth was not particularly hot even in those early days4 ,the gentle progressive change of climate which is recorded in the rocks appears to have been only in slight measure a change in the mean temperature of the earth as a whole1 and almost entirely a change in the distribution of temperature from place to place and season to season4 ,hence it seems probable that neither the earth's own emission of heat1 nor the supply of solar heat1 nor the power of the atmosphere to retain heat can have been much greater a few hundred million years ago than now4 ,it is indeed possible that these three factors may have varied in such a way that any variation in one has been offset by variations of the others in the opposite direction4 ,this1 however1 is so highly improbable that it seems advisable to assume that all three have remained relatively constant4 ,this conclusion together with a realization of the climatic significance of carbon dioxide has forced most of the adherents of the nebular hypothesis to abandon their assumption that carbon dioxide1 the heaviest gas in the air1 was very abundant until taken out by coal-forming plants or combined with the calcium oxide of igneous rocks to form the limestone secreted by animals4 ,in the same way the presence of sun cracks in sedimentary rocks of all ages suggests that the air cannot have contained vast quantities of water vapor such as have been assumed by ,knowlton and others in order to account for the former lack of sharp climatic contrast between the zones4 ,such a large amount of water vapor would almost certainly be accompanied by well-nigh universal and continual cloudiness so that there would be little chance for the pools on the earth's water-soaked surface to dry up4 ,furthermore1 there is only one way in which such cloudiness could be maintained and that is by keeping the air at an almost constant temperature night and day4 ,this would require that the chief source of warmth be the interior of the earth1 a condition which the ,proterozoic1 ,permian1 and other widespread glaciations seem to disprove4 ,thus there appears to be strong evidence against the radical changes in the atmosphere which are sometimes postulated4 ,yet some changes must have taken place1 and even minor changes would be accompanied by some sort of climatic effect4 ,the changes would take the form of either an increase or a decrease in the atmosphere as a whole1 or in its constituent elements4 ,the chief means by which the atmosphere has increased appear to be as follows3 7a7 ,by contributions from the interior of the earth via volcanoes and springs and by the weathering of igneous rocks with the consequent release of their enclosed gases2#ajf 7b7 by the escape of some of the abundant gases which the ocean holds in solution2 7c7 by the arrival on the earth of gases from space1 either enclosed in meteors or as free-flying molecules2 7d7 by the release of gases from organic compounds by oxidation1 or by exhalation from animals and plants4 ,on the other hand1 one or another of the constituents of the atmosphere has presumably decreased 7a7 by being locked up in newly formed rocks or organic compounds2 7b7 by being dissolved in the ocean2 7c7 by the escape of molecules into space2 and 7d7 by the condensation of water vapor4 ,the combined effect of the various means of increase and decrease depends partly on the amount of each constituent received from the earth's interior or from space1 and partly on the fact that the agencies which tend to deplete the atmosphere are highly selective in their action4 ,our knowledge of how large a quantity of new gases the air has received is very scanty1 but judging by present conditions the general tendency is toward a slow increase chiefly because of meteorites1 volcanic action1 and the work of deep-seated springs4 ,as to decrease1 the case is clearer4 ,this is because the chemically active gases1 oxygen1 ,,co#b1 and water vapor1 tend to be locked up in the rocks1 while the chemically inert gases1 nitrogen and argon1 show almost no such tendency4 ,though oxygen is by far the most abundant element in the earth's crust1 making up more than #ej per cent of the total1 it forms only about one-fifth of the air4 ,nitrogen1 on the other hand1 is very rare in the rocks1 but makes up nearly four-fifths of the air4 ,it would1 therefore1 seem probable that throughout the earth's history1 there has been a progressive increase in the amount of atmospheric nitrogen1 and presumably a somewhat corresponding increase in the mass of the air4 ,on the other hand1 it is not clear what changes have occurred in the amount of atmospheric oxygen4 ,it may have increased somewhat or perhaps even notably4 ,nevertheless1 because of the greater increase in nitrogen1 it may form no greater percentage of the air now than in the distant past4 ,as to the absolute amounts of oxygen1 ,barrell#ajg thought that atmospheric oxygen began to be present only after plants had appeared4 ,it will be recalled that plants absorb carbon dioxide and separate the carbon from the oxygen1 using the carbon in their tissues and setting free the oxygen4 ,as evidence of a paucity of oxygen in the air in early ,proterozoic times1 ,barrell cites the fact that the sedimentary rocks of that remote time commonly are somewhat greyish or greenish-grey wackes1 or other types1 indicating incomplete oxidation4 ,he admits1 however1 that the stupendous thicknesses of red sandstones1 quartzite1 and hematitic iron ores of the later ,proterozoic prove that by that date there was an abundance of atmospheric oxygen4 ,if so1 the change from paucity to abundance must have occurred before fossils were numerous enough to give much clue to climate4 ,however1 ,barrell's evidence as to a former paucity of atmospheric oxygen is not altogether convincing4 ,in the first place1 it does not seem justifiable to assume that there could be no oxygen until plants appeared to break down the carbon dioxide1 for some oxygen is contributed by volcanoes1#ajh and lightning decomposes water into its elements4 ,part of the hydrogen thus set free escapes into space1 for the earth's gravitative force does not appear great enough to hold this lightest of gases1 but the oxygen remains4 ,thus electrolysis of water results in the accumulation of oxygen4 ,in the second place1 there is no proof that the ancient greywackes are not deoxidized sediments4 ,light colored rock formations do not necessarily indicate a paucity of atmospheric oxygen1 for such rocks are abundant even in recent times4 ,for example1 the ,tertiary formations are characteristically light colored1 a result1 however1 of deoxidation4 ,finally1 the fact that sedimentary rocks1 irrespective of their age1 contain an average of about #a4e per cent more oxygen than do igneous rocks1#aji suggests that oxygen was present in the air in quantity even when the earliest shales and sandstones were formed1 for atmospheric oxygen seems to be the probable source of the extra oxygen they contain4 ,the formation of these particular sedimentary rocks by weathering of igneous rocks involves only a little carbon dioxide and water4 ,although it seems probable that oxygen was present in the atmosphere even at the beginning of the geological record1 it may have been far less abundant then than now4 ,it may have been removed from the atmosphere by animals or by the oxidation of the rocks almost as rapidly as it was added by volcanoes1 plants1 and other agencies4 ,after this chapter was in type1 ,st4 ,john,c announced his interesting discovery that oxygen is apparently lacking in the atmosphere of ,venus4 ,he considers that this proves that ,venus has no life4 ,furthermore he concludes that so active an element as oxygen cannot be abundant in the atmosphere of a planet unless plants continually supply large quantities by breaking down carbon dioxide4 ,but even if the earth has experienced a notable increase in atmospheric oxygen since the appearance of life1 this does not necessarily involve important climatic changes except those due to increased atmospheric density4 ,this is because oxygen has very little effect upon the passage of light or heat1 being transparent to all but a few wave lengths4 ,those absorbed are chiefly in the ultra violet4 ,the distinct possibility that oxygen has increased in amount1 makes it the more likely that there has been an increase in the total atmosphere1 for the oxygen would supplement the increase in the relatively inert nitrogen and argon1 which has presumably taken place4 ,the climatic effects of an increase in the atmosphere include1 in the first place1 an increased scattering of light as it approaches the earth4 ,nitrogen1 argon1 and oxygen all scatter the short waves of light and thus interfere with their reaching the earth4 ,abbot and ,fowle1#aaj who have carefully studied the matter1 believe that at present the scattering is quantitatively important in lessening insolation4 ,hence our supposed general increase in the volume of the air during part of geological times would tend to reduce the amount of solar energy reaching the earth's surface4 ,on the other hand1 nitrogen and argon do not appear to absorb the long wave lengths known as heat1 and oxygen absorbs so little as to be almost a non-absorber4 ,therefore the reduced penetration of the air by solar radiation due to the scattering of light would apparently not be neutralized by any direct increase in the blanketing effect of the atmosphere1 and the temperature near the earth's surface would be slightly lowered by a thicker atmosphere4 ,this would diminish the amount of water vapor which would be held in the air1 and thereby lower the temperature a trifle more4 ,in the second place1 the higher atmospheric pressure which would result from the addition of gases to the air would cause a lessening of the rate of evaporation1 for that rate declines as pressure increases4 ,decreased evaporation would presumably still further diminish the vapor content of the atmosphere4 ,this would mean a greater daily and seasonal range of temperature1 as is very obvious when we compare clear weather with cloudy4 ,cloudy nights are relatively warm while clear nights are cool1 because water vapor is an almost perfect absorber of radiant heat1 and there is enough of it in the air on moist nights to interfere greatly with the escape of the heat accumulated during the day4 ,therefore1 if atmospheric moisture were formerly much more abundant than now1 the temperature must have been much more uniform4 ,the tendency toward climatic severity as time went on would be still further increased by the cooling which would result from the increased wind velocity discussed below2 for cooling by convection increases with the velocity of the wind1 as does cooling by conduction4 ,any persistent lowering of the general temperature of the air would affect not only its ability to hold water vapor1 but would produce a lessening in the amount of atmospheric carbon dioxide1 for the colder the ocean becomes the more carbon dioxide it can hold in solution4 ,when the oceanic temperature falls1 part of the atmospheric carbon dioxide is dissolved in the ocean4 ,this minor constituent of the air is important because although it forms only #j4jjc per cent of the earth's atmosphere1 ,abbot and ,fowle's#aaa calculations indicate that it absorbs over #aj per cent of the heat radiated outward from the earth4 ,hence variations in the amount of carbon dioxide may have caused an appreciable variation in temperature and thus in other climatic conditions4 ,humphreys1 as we have seen1 has calculated that a doubling of the carbon dioxide in the air would directly raise the earth's temperature to the extent of #a4c deg4,c41 and a halving would lower it a like amount4 ,the indirect results of such an increase or decrease might be greater than the direct results1 for the change in temperature due to variations in carbon dioxide would alter the capacity of the air to hold moisture4 ,two conditions would especially help in this respect2 first1 changes in nocturnal cooling1 and second1 changes in local convection4 ,the presence of carbon dioxide diminishes nocturnal cooling because it absorbs the heat radiated by the earth1 and re-radiates part of it back again4 ,hence with increased carbon dioxide and with the consequent warmer nights there would be less nocturnal condensation of water vapor to form dew and frost4 ,local convection is influenced by carbon dioxide because this gas lessens the temperature gradient4 ,in general1 the less the gradient1 that is1 the less the contrast between the temperature at the surface and higher up1 the less convection takes place4 ,this is illustrated by the seasonal variation in convection4 ,in summer1 when the gradient is steepest1 convection reaches its maximum4 ,it will be recalled that when air rises it is cooled by expansion1 and if it ascends far the moisture is soon condensed and precipitated4 ,indeed1 local convection is considered by ,c4 ,p4 ,day to be the chief agency which keeps the lower air from being continually saturated with moisture4 ,the presence of carbon dioxide lessens convection because it increases the absorption of heat in the zone above the level in which water vapor is abundant1 thus warming these higher layers4 ,the lower air may not be warmed correspondingly by an increase in carbon dioxide if ,abbot and ,fowle are right in stating that near the earth's surface there is enough water vapor to absorb practically all the wave lengths which carbon dioxide is capable of absorbing4 ,hence carbon dioxide is chiefly effective at heights to which the low temperature prevents water vapor from ascending4 ,carbon dioxide is also effective in cold winters and in high latitudes when even the lower air is too cold to contain much water vapor4 ,moreover1 carbon dioxide1 by altering the amount of atmospheric water vapor1 exerts an indirect as well as a direct effect upon temperature4 ,other effects of the increase in air pressure which we are here assuming during at least the early part of geological times are corresponding changes in barometric contrasts1 in the strength of winds1 and in the mass of air carried by the winds along the earth's surface4 ,the increase in the mass of the air would reenforce the greater velocity of the winds in their action as eroding and transporting agencies4 ,because of the greater weight of the air1 the winds would be capable of picking up more dust and of carrying it farther and higher2 while the increased atmospheric friction would keep it aloft a longer time4 ,the significance of dust at high levels and its relation to solar radiation have already been discussed in connection with volcanoes4 ,it will be recalled that on the average it lowers the surface temperature4 ,at lower levels1 since dust absorbs heat quickly and gives it out quickly1 its presence raises the temperature of the air by day and lowers it by night4 ,hence an increase in dustiness tends toward greater extremes4 ,from all these considerations it appears that if the atmosphere has actually evolved according to the supposition which is here tentatively entertained1 the general tendency of the resultant climatic changes must have been partly toward long geological oscillations and partly toward a general though very slight increase in climatic severity and in the contrasts between the zones4 ,this seems to agree with the geological record1 although the fact that we are living in an age of relative climatic severity may lead us astray4 ,the significant fact about the whole matter is that the three great types of terrestrial agencies1 namely1 those of the earth's interior1 those of the oceans1 and those of the air1 all seem to have suffered changes which lead to slow variations of climate4 ,many reversals have doubtless taken place1 and the geologic oscillations thus induced are presumably of much greater importance than the progressive change1 yet so far as we can tell the purely terrestrial changes throughout the hundreds of millions of years of geological time have tended toward complexity and toward increased contrasts from continent to ocean1 from latitude to latitude1 from season to season1 and from day to night4 ,throughout geological history the slow and almost imperceptible differentiation of the earth's surface has been one of the most noteworthy of all changes4 ,it has been opposed by the extraordinary conservatism of the universe which causes the average temperature today to be so like that of hundreds of millions of years ago that many types of life are almost identical4 ,nevertheless1 the differentiation has gone on4 ,often1 to be sure1 it has presumably been completely masked by the disturbances of the solar atmosphere which appear to have been the cause of the sharper1 shorter climatic pulsations4 ,but regardless of cosmic conservatism and of solar impulses toward change1 the slow differentiation of the earth's surface has apparently given to the world of today much of the geographical complexity which is so stimulating a factor in organic evolution4 ,such complexity--such diversity from place to place--appears to be largely accounted for by purely terrestrial causes4 ,it may be regarded as the great terrestrial contribution to the climatic environment which guides the development of life4 ,,footnotes3 ,footnote #ig3 ,encyclopaedia ,britannica1 #aath edition3 article ,ocean4 ,footnote #ih3 ,c4 ,e4 ,p4 ,brooks3 ,the ,meteorological ,conditions of an ,ice sheet and ,their ,bearing on the ,desiccation of the ,globe2 ,quart4 ,jour4 ,royal ,meteorol4 ,soc41 ,vol4 #dj1 #aiad1 pp4 #ec-gj4 ,footnote #ii3 ,data of ,geochemistry1 ,fourth ,ed41 #aibj2 ,bull4 ,no4 #fie1 ,u4 ,s4 ,geol4 ,survey4 ,footnote #ajj3 ,quoted by ,schuchert in ,the ,evolution of the ,earth4 ,footnote #aja3 ,smithsonian ,physical ,tables1 ,sixth ,revision1 #aiad1 p4 #adb4 ,footnote #ajb3 ,chamberlin1 in a very suggestive article ,on a possible reversal of oceanic circulation 7,jour4 of ,geol41 ,vol4 #ad1 pp4 #cfc-cgc1 #aijf71 discusses the probable climatic consequences of a reversal in the direction of deep-sea circulation4 ,it is not wholly beyond the bounds of possibility that1 in the course of ages the increasing drainage of salt from the lands not only by nature but by man's activities in agriculture and drainage1 may ultimately cause such a reversal by increasing the ocean's salinity until the more saline tropical portion is heavier than the cooler but fresher subpolar waters4 ,if that should happen1 ,greenland1 ,antarctica1 and the northern shores of ,america and ,asia would be warmed by the tropical heat which had been transferred poleward beneath the surface of the ocean1 without loss en route4 ,subpolar regions1 under such a condition of reversed deep-sea circulation1 might have a mild climate4 ,indeed1 they might be among the world's most favorable regions climatically4 ,footnote #ajc3 ,encyclopaedia ,britannica3 article ,ocean4 ,footnote #ajd3 ,chamberlin and ,salisbury3 ,geology1 ,vol4 ,,ii1 pp4 #a-acb1 #aijf2 and ,t4 ,c4 ,chamberlin3 ,the ,origin of the ,earth1 #aiaf4 ,footnote #aje3 ,personal communication4 ,footnote #ajf3 ,r4 ,t4 ,chamberlin3 ,gases in ,rocks1 ,carnegie ,inst4 of ,wash41 ,no4 #ajf1 #aijh4 ,footnote #ajg3 ,j4 ,barrell3 ,the ,origin of the ,earth1 in ,evolution of the ,earth and ,its ,inhabitants1 #aiah1 p4 #dd1 and more fully in an unpublished manuscript4 ,footnote #ajh3 ,f4 ,w4 ,clarke3 ,data of ,geochemistry1 ,fourth ,ed41 #aibj1 ,bull4 ,no4 #fie1 ,u4 ,s4 ,geol4 ,survey1 p4 #bef4 ,footnote #aji3 ,f4 ,w4 ,clarke3 loc4 cit41 pp4 #bg-cd et al4 ,footnote ,c3 ,chas4 ,e4 ,st4 ,john3 ,science ,service ,press ,reports from the ,mt4 ,wilson ,observatory1 ,may1 #aibb4 ,footnote #aaj3 ,abbot and ,fowle3 ,annals ,astrophysical ,observatory2 ,smiths4 ,inst41 ,vol4 ,,ii1 #aijh1 p4 #afc4 ,f4 ,e4 ,fowle3 ,atmospheric ,scattering of ,light2 ,misc4 ,coll4 ,smiths4 ,inst41 ,vol4 #fi1 #aiah4 ,footnote #aaa3 ,abbot and ,fowle3 loc4 cit41 p4 #agb4 ,,chapter ,,xiv ,,the ,,effect ,,of ,,other ,,bodies ,,on ,,the ,,sun ,if solar activity is really an important factor in causing climatic changes1 it behooves us to subject the sun to the same kind of inquiry to which we have subjected the earth4 ,we have inquired into the nature of the changes through which the earth's crust1 the oceans1 and the atmosphere have influenced the climate of geological times4 ,it has not been necessary1 however1 to study the origin of the earth1 nor to trace its earlier stages4 ,our study of the geological record begins only when the earth had attained practically its present mass1 essentially its present shape1 and a climate so similar to that of today that life as we know it was possible4 ,in other words1 the earth had passed the stages of infancy1 childhood1 youth1 and early maturity1 and had reached full maturity4 ,as it still seems to be indefinitely far from old age1 we infer that during geological times its relative changes have been no greater than those which a man experiences between the ages of perhaps twenty-five and forty4 ,similar reasoning applies with equal or greater force to the sun4 ,because of its vast size it presumably passes through its stages of development much more slowly than the earth4 ,in the first chapter of this book we saw that the earth's relative uniformity of climate for hundreds of millions of years seems to imply a similar uniformity in solar activity4 ,this accords with a recent tendency among astronomers who are more and more recognizing that the stars and the solar system possess an extraordinary degree of conservatism4 ,changes that once were supposed to take place in thousands of years are now thought to have required millions4 ,hence in this chapter we shall assume that throughout geological times the condition of the sun has been almost as at present4 ,it may have been somewhat larger1 or different in other ways1 but it was essentially a hot1 gaseous body such as we see today and it gave out essentially the same amount of energy4 ,this assumption will affect the general validity of what follows only if it departs widely from the truth4 ,with this assumption1 then1 let us inquire into the degree to which the sun's atmosphere has probably been disturbed throughout geological times4 ,in ,earth and ,sun1 as already explained1 a detailed study has led to the conclusion that cyclonic storms are influenced by the electrical action of the sun4 ,such action appears to be most intense in sunspots1 but apparently pertains also to other disturbed areas in the sun's atmosphere4 ,a study of sunspots suggests that their true periodicity is almost if not exactly identical with that of the orbital revolution of ,jupiter1 #aa4h years4 ,other investigations show numerous remarkable coincidences between sunspots and the orbital revolution of the other planets1 including especially ,saturn and ,mercury4 ,this seems to indicate that there is some truth in the hypothesis that sunspots and other related disturbances of the solar atmosphere owe their periodicity to the varying effects of the planets as they approach and recede from the sun in their eccentric orbits and as they combine or oppose their effects according to their relative positions4 ,this does not mean that the energy of the solar disturbances is supposed to come from the planets1 but merely that their variations act like the turning of a switch to determine when and how violently the internal forces of the sun shall throw the solar atmosphere into commotion4 ,this hypothesis is by no means new1 for in one form or another it has been advocated by ,wolfer1 ,birkeland1 ,e4 ,w4 ,brown1 ,schuster1 ,arctowski1 and others4 ,the agency through which the planets influence the solar atmosphere is not yet clear4 ,the suggested agencies are the direct pull of gravitation1 the tidal effect of the planets1 and an electro-magnetic effect4 ,in ,earth and ,sun the conclusion is reached that the first two are out of the question1 a conclusion in which ,e4 ,w4 ,brown acquiesces4 ,unless some unknown cause is appealed to1 this leaves an electro-magnetic hypothesis as the only one which has a reasonable foundation4 ,schuster inclines to this view4 ,the conclusions set forth in ,earth and ,sun as to the electrical nature of the sun's influence on the earth point somewhat in the same direction4 ,hence in this chapter we shall inquire what would happen to the sun1 and hence to the earth1 on their journey through space1 if the solar atmosphere is actually subject to disturbance by the electrical or other effects of other heavenly bodies4 ,it need hardly be pointed out that we are here venturing into highly speculative ground1 and that the verity or falsity of the conclusions reached in this chapter has nothing to do with the validity of the reasoning in previous chapters4 ,those chapters are based on the assumption that terrestrial causes of climatic changes are supplemented by solar disturbances which produce their effect partly through variations in temperature but also through variations in the intensity and paths of cyclonic storms4 ,the present chapter seeks to shed some light on the possible causes and sequence of solar disturbances4 ,let us begin by scanning the available evidence as to solar disturbances previous to the time when accurate sunspot records are available4 ,two rather slender bits of evidence point to cycles of solar activity lasting hundreds of years4 ,one of these has already been discussed in ,chapter ,,vi1 where the climatic stress of the fourteenth century was described4 ,at that time sunspots are known to have been unusually numerous1 and there were great climatic extremes4 ,lakes overflowed in ,central ,asia2 storms1 droughts1 floods1 and cold winters were unusually severe in ,europe2 the ,caspian ,sea rose with great rapidity2 the trees of ,california grew with a vigor unknown for centuries2 the most terrible of recorded famines occurred in ,england and ,india2 the ,eskimos were probably driven south by increasing snowiness in ,greenland2 and the ,mayas of ,yucatan appear to have made their last weak attempt at a revival of civilization under the stimulus of greater storminess and less constant rainfall4 ,the second bit of evidence is found in recent exhaustive studies of periodicities by ,turner#aab and other astronomers4 ,they have sought every possible natural occurrence for which a numerical record is available for a long period4 ,the most valuable records appear to be those of tree growth1 ,nile floods1 ,chinese earthquakes1 and sunspots4 ,turner reaches the conclusion that all four types of phenomena show the same periodicity1 namely1 cycles with an average length of about #bfj to #bhj years4 ,he suggests that if this is true1 the cycles in tree growth and in floods1 both of which are climatic1 are probably due to a non-terrestrial cause4 ,the fact that the sunspots show similar cycles suggests that the sun's variations are the cause4 ,these two bits of evidence are far too slight to form the foundation of any theory as to changes in solar activity in the geological past4 ,nevertheless it may be helpful to set forth certain possibilities as a stimulus to further research4 ,for example1 it has been suggested that meteoric bodies may have fallen into the sun and caused it suddenly to flare up1 as it were4 ,this is not impossible1 although it does not appear to have taken place since men became advanced enough to make careful observations4 ,moreover1 the meteorites which now fall on the earth are extremely small1 the average size being computed as no larger than a grain of wheat4 ,the largest ever found on the earth's surface1 at ,bacubirito in ,mexico1 weighs only about fifty tons1 while within the rocks the evidences of meteorites are extremely scanty and insignificant4 ,if meteorites had fallen into the sun often enough and of sufficient size to cause glacial fluctuations and historic pulsations of climate1 it seems highly probable that the earth would show much more evidence of having been similarly disturbed4 ,and even if the sun should be bombarded by large meteors the result would probably not be sudden cold periods1 which are the most notable phenomena of the earth's climatic history1 but sudden warm periods followed by slow cooling4 ,nevertheless1 the disturbance of the sun by collision with meteoric matter can by no means be excluded as a possible cause of climatic variations4 ,allied to the preceding hypothesis is ,shapley's#aac nebular hypothesis4 ,at frequent intervals1 averaging about once a year during the last thirty years1 astronomers have discovered what are known as novae4 ,these are stars which were previously faint or even invisible1 but which flash suddenly into brilliancy4 ,often their light-giving power rises seven or eight magnitudes--a thousand-fold4 ,in addition to the spectacular novae there are numerous irregular variables whose brilliancy changes in every ratio from a few per cent up to several magnitudes4 ,most of them are located in the vicinity of nebulae1 as is also the case with novae4 ,this1 as well as other facts1 makes it probable that all these stars are friction variables1 as ,shapley calls them4 ,apparently as they pass through the nebulae they come in contact with its highly diffuse matter and thereby become bright much as the earth would become bright if its atmosphere were filled with millions of almost infinitesimally small meteorites4 ,a star may also lose brilliancy if nebulous matter intervenes between it and the observer4 ,if our sun has been subjected to any of these changes some sort of climatic effect must have been produced4 ,in a personal communication ,shapley amplifies the nebular climatic hypothesis as follows3 ,within #gjj light years of the sun in many directions 7,taurus1 ,cygnus1 ,ophiuchus1 ,scorpio7 are great diffuse clouds of nebulosity1 some bright1 most of them dark4 ,the probability that stars moving in the general region of such clouds will encounter this material is very high1 for the clouds fill enormous volumes of space1--e4g41 probably more than a hundred thousand cubic light years in the ,orion region1 and are presumably composed of rarefied gases or of dust particles4 ,probably throughout all our part of space such nebulosity exists 7it is all around us1 we are sure71 but only in certain regions is it dense enough to affect conspicuously the stars involved in it4 ,if a star moving at high velocity should collide with a dense part of such a nebulous cloud1 we should probably have a typical nova4 ,if the relative velocity of nebulous material and star were low or moderate1 or if the material were rare1 we should not expect a conspicuous effect on the star's light4 ,in the nebulous region of ,orion1 which is probably of unusually high density1 there are about #ajj known stars1 varying between #bj and #hj of their total light--all of them irregularly--some slowly1 some suddenly4 ,apparently they are friction variables4 ,some of the variables suddenly lose #dj of their light as if blanketed by nebulous matter4 ,in the ,trifid ,nebula there are variables like those of ,orion1 in ,messier #h also1 and probably many of the #ajj or so around the ,rho ,ophiuchi region belong to this kind4 ,i believe that our sun could not have been a typical nova1 at least not since the ,archeozoic1 that is for perhaps a billion years4 ,i believe we have in geological climates final proof of this1 because an increase in the amount of solar radiation by #ajjj times as in the typical nova1 would certainly punctuate emphatically the life cycle on the earth1 even if the cause of the nova would not at the same time eliminate the smaller planets4 ,but the sun may have been one of these miniature novae or friction variables2 and ,i believe it very probable that its wanderings through this part of space could not long leave its mean temperature unaffected to the amount of a few per cent4 ,one reason we have not had this proposal insisted upon before is that the data back of it are mostly new--the ,orion variables have been only recently discovered and studied1 the distribution and content of the dark nebulae are hardly as yet generally known4 ,this interesting hypothesis cannot be hastily dismissed4 ,if the sun should pass through a nebula it seems inevitable that there would be at least slight climatic effects and perhaps catastrophic effects through the action of the gaseous matter not only on the sun but on the earth's own atmosphere4 ,as an explanation of the general climatic conditions of the past1 however1 ,shapley points out that the hypothesis has the objection of being vague1 and that nebulosity should not be regarded as more than a possible factor4 ,one of the chief difficulties seems to be the enormously wide distribution of as yet undiscovered nebulous matter which must be assumed if any large share of the earth's repeated climatic changes is to be ascribed to such matter4 ,if such matter is actually abundant in space1 it is hard to see how any but the nearest stars would be visible4 ,another objection is that there is no known nebulosity near at hand with which to connect the climatic vicissitudes of the last glacial period4 ,moreover1 the known nebulae are so much less numerous than stars that the chances that the sun will encounter one of them are extremely slight4 ,this1 however1 is not an objection1 for ,shapley points out that during geological times the sun can never have varied as much as do the novae1 or even as most of the friction variables4 ,thus the hypothesis stands as one that is worth investigating1 but that cannot be finally rejected or accepted until it is made more definite and until more information is available4 ,another suggested cause of solar variations is the relatively sudden contraction of the sun such as that which sometimes occurs on the earth when continents are uplifted and mountains upheaved4 ,it seems improbable that this could have occurred in a gaseous body like the sun4 ,lacking1 as it does1 any solid crust which resists a change of form1 the sun probably shrinks steadily4 ,hence any climatic effects thus produced must be extremely gradual and must tend steadily in one direction for millions of years4 ,still another suggestion is that the tidal action of the stars and other bodies which may chance to approach the sun's path may cause disturbances of the solar atmosphere4 ,the vast kaleidoscope of space is never quiet4 ,the sun1 the stars1 and all the other heavenly bodies are moving1 often with enormous speed4 ,hence the effect of gravitation upon the sun must vary constantly and irregularly1 as befits the geological requirements4 ,in the case of the planets1 however1 the tidal effect does not seem competent to produce the movements of the solar atmosphere which appear to be concerned in the inception of sunspots4 ,moreover1 there is only the most remote probability that a star and the sun will approach near enough to one another to produce a pronounced gravitational disturbance in the solar atmosphere4 ,for instance1 if it be assumed that changes in ,jupiter's tidal effect on the sun are the main factor in regulating the present difference between sunspot maxima and sunspot minima1 the chances that a star or some non-luminous body of similar mass will approach near enough to stimulate solar activity and thereby bring on glaciation are only one in twelve billion years1 as will be explained below4 ,this seems to make a gravitational hypothesis impossible4 ,another possible cause of solar disturbances is that the stars in their flight through space may exert an electrical influence which upsets the equilibrium of the solar atmosphere4 ,at first thought this seems even more impossible than a gravitational effect4 ,electrostatic effects1 however1 differ greatly from those of tides4 ,they vary as the diameter of a body instead of as its mass2 their differentials also vary inversely as the square of the distance instead of as the cube4 ,electrostatic effects also increase as the fourth power of the temperature or at least would do so if they followed the law of black bodies2 they are stimulated by the approach of one body to another2 and they are cumulative1 for if ions arrive from space they must accumulate until the body to which they have come begins to discharge them4 ,hence1 on the basis of assumptions such as those used in the preceding paragraph1 the chances of an electrical disturbance of the solar atmosphere sufficient to cause glaciation on the earth may be as high as one in twenty or thirty million years4 ,this seems to put an electrical hypothesis within the bounds of possibility4 ,further than that we cannot now go4 ,there may be other hypotheses which fit the facts much better1 but none seems yet to have been suggested4 ,in the rest of this chapter the tidal and electrical hypotheses of stellar action on the sun will be taken up in detail4 ,the tidal hypothesis is considered because in discussions of the effect of the planets it has hitherto held almost the entire field4 ,the electrical hypothesis will be considered because it appears to be the best yet suggested1 although it still seems doubtful whether electrical effects can be of appreciable importance over such vast distances as are inevitably involved4 ,the discussion of both hypotheses will necessarily be somewhat technical1 and will appeal to the astronomer more than to the layman4 ,it does not form a necessary part of this book1 for it has no bearing on our main thesis of the effect of the sun on the earth4 ,it is given here because ultimately the question of changes in solar activity during geological times must be faced4 ,in the astronomical portion of the following discussion we shall follow ,jeans#aad in his admirable attempt at a mathematical analysis of the motions of the universe4 ,jeans divides the heavenly bodies into five main types4 7#a7 ,spiral nebulae1 which are thought by some astronomers to be systems like our own in the making1 and by others to be independent universes lying at vast distances beyond the limits of our ,galactic universe1 as it is called from the ,galaxy or ,milky ,way4 7#b7 ,nebulae of a smaller type1 called planetary4 ,these lie within the ,galactic portion of the universe and seem to be early stages of what may some day be stars or solar systems4 7#c7 ,binary or multiple stars1 which are extraordinarily numerous4 ,in some parts of the heavens they form #ej or even #fj per cent of the stars and in the galaxy as a whole they seem to form fully one third4 7#d7 ,star clusters4 ,these consist of about a hundred groups of stars in each of which the stars move together in the same direction with approximately the same velocity4 ,these1 like the spiral nebulae1 are thought by some astronomers to lie outside the limits of the galaxy1 but this is far from certain4 7#e7 ,the solar system4 ,according to ,jeans this seems to be unique4 ,it does not fit into the general mathematical theory by which he explains spiral nebulae1 planetary nebulae1 binary stars1 and star clusters4 ,it seems to demand a special explanation1 such as is furnished by tidal disruption due to the passage of the sun close to another star4 ,the part of ,jeans' work which specially concerns us is his study of the probability that some other star will approach the sun closely enough to have an appreciable gravitative or electrical effect1 and thus cause disturbances in the solar atmosphere4 ,of course both the star and the sun are moving1 but to avoid circumlocution we shall speak of such mutual approaches simply as approaches of the sun4 ,for our present purpose the most fundamental fact may be summed up in a quotation from ,jeans in which he says that most stars show evidence of having experienced considerable disturbance by other systems2 there is no reason why our solar system should be expected to have escaped the common fate4 ,jeans gives a careful calculation from which it is possible to derive some idea of the probability of any given degree of approach of the sun and some other star4 ,of course all such calculations must be based on certain assumptions4 ,the assumptions made by ,jeans are such as to make the probability of close approaches as great as possible4 ,for example1 he allows only #efj million years for the entire evolution of the sun1 whereas some astronomers and geologists would put the figure ten or more times as high4 ,nevertheless1 ,jeans' assumptions at least show the order of magnitude which we may expect on the basis of reasonable astronomical conclusions4 ,according to the planetary hypothesis of sunspots1 the difference in the effect of ,jupiter when it is nearest and farthest from the sun is the main factor in starting the sunspot cycle and hence the corresponding terrestrial cycle4 ,the climatic difference between sunspot maxima and minima1 as measured by temperature1 apparently amounts to at least a twentieth and perhaps a tenth of the difference between the climate of the last glacial epoch and the present4 ,we may suppose1 then1 that a body which introduced a gravitative or electrical factor twenty times as great as the difference in ,jupiter's effect at its maximum and minimum distances from the sun would cause a glacial epoch if the effect lasted long enough4 ,of course the other planets combine their effects with that of ,jupiter1 but for the sake of simplicity we will leave the others out of account4 ,the difference between ,jupiter's maximum and minimum tidal effect on the sun amounts to #bi per cent of the planet's average effect4 ,the corresponding difference1 according to the electrical hypothesis1 is about #ai per cent1 for electrostatic action varies as the square of the distance instead of as the cube4 ,let us assume that a body exerting four times ,jupiter's present tidal effect and placed at the average distance of ,jupiter from the sun would disturb the sun's atmosphere twenty times as much as the present difference between sunspot maxima and minima1 and thus1 perhaps1 cause a glacial period on the earth4 ,on the basis of this assumption our first problem is to estimate the frequency with which a star1 visible or dark1 is likely to approach near enough to the sun to produce a tidal effect four times that of ,jupiter4 ,the number of visible stars is known or at least well estimated4 ,as to dark stars1 which have grown cool1 ,arrhenius believed that they are a hundred times as numerous as bright stars2 few astronomers believe that there are less than three or four times as many4 ,dr4 ,shapley of the ,harvard ,observatory states that a new investigation of the matter suggests that eight or ten is probably a maximum figure4 ,let us assume that nine is correct4 ,the average visible star1 so far as measured1 has a mass about twice that of the sun1 or about #bajj times that of ,jupiter4 ,the distances of the stars have been measured in hundreds of cases and thus we can estimate how many stars1 both visible and invisible1 are on an average contained in a given volume of space4 ,on this basis ,jeans estimates that there is only one chance in thirty billion years that a visible star will approach within #b4h times the distance of ,neptune from the sun1 that is1 within about eight billion miles4 ,if we include the invisible stars the chances become one in three billion years4 ,in order to produce four times the tidal effect of ,jupiter1 however1 the average star would have to approach within about four billion miles of the sun1 and the chances of that are only one in twelve billion years4 ,the disturbing star would be only #dj per cent farther from the sun than ,neptune1 and would almost pass within the solar system4 ,even though ,jeans holds that the frequency of the mutual approach of the sun and a star was probably much greater in the distant past than at present1 the figures just given lend little support to the tidal hypothesis4 ,in fact1 they apparently throw it out of court4 ,it will be remembered that ,jeans has made assumptions which give as high a frequency of stellar encounters as is consistent with the astronomical facts4 ,we have assumed nine dark stars for every bright one1 which may be a liberal estimate4 ,also1 although we have assumed that a disturbance of the sun's atmosphere sufficient to cause a glacial period would arise from a tidal effect only twenty times as great as the difference in ,jupiter's effect when nearest the sun and farthest away1 in our computations this has actually been reduced to thirteen4 ,with all these favorable assumptions the chances of a stellar approach of the sort here described are now only one in twelve billion years4 ,yet within a hundred million years1 according to many estimates of geological time1 and almost certainly within a billion1 there have been at least half a dozen glaciations4 ,our use of ,jeans' data interposes another and equally insuperable difficulty to any tidal hypothesis4 ,four billion miles is a very short distance in the eyes of an astronomer4 ,at that distance a star twice the size of the sun would attract the outer planets more strongly than the sun itself1 and might capture them4 ,if a star should come within four billion miles of the sun1 its effect in distorting the orbits of all the planets would be great4 ,if this had happened often enough to cause all the glaciations known to geologists1 the planetary orbits would be strongly elliptical instead of almost circular4 ,the consideration here advanced militate so strongly against the tidal hypothesis of solar disturbances that it seems scarcely worth while to consider it further4 ,let us turn now to the electrical hypothesis4 ,here the conditions are fundamentally different from those of the tidal hypothesis4 ,in the first place the electrostatic effect of a body has nothing to do with its mass1 but depends on the area of its surface2 that is1 it varies as the square of the radius4 ,second1 the emission of electrons varies exponentially4 ,if hot glowing stars follow the same law as black bodies at lower temperatures1 the emission of electrons1 like the emission of other kinds of energy1 varies as the fourth power of the absolute temperature4 ,in other words1 suppose there are two black bodies1 otherwise alike1 but one with a temperature of #bg deg4 ,c4 or #cjj deg4 on the absolute scale1 and the other with #fjj deg4 on the absolute scale4 ,the temperature of one is twice as high as that of the other1 but the electrostatic effect will be sixteen times as great4#aae ,third1 the number of electrons that reach a given body varies inversely as the square of the distance1 instead of as the cube which is the case with tide-making forces4 ,in order to use these three principles in calculating the effect of the stars we must know the diameters1 distances1 temperature1 and number of the stars4 ,the distances and number may safely be taken as given by ,jeans in the calculations already cited4 ,as to the diameters1 the measurements of the stars thus far made indicate that the average mass is about twice that of the sun4 ,the average density1 as deduced by ,shapley#aaf from the movements of double stars1 is about one-eighth the solar density4 ,this would give an average diameter about two and a half times that of the sun4 ,for the dark stars1 we shall assume for convenience that they are ten times as numerous as the bright ones4 ,we shall also assume that their diameter is half that of the sun1 for being cool they must be relatively dense1 and that their temperature is the same as that which we shall assume for ,jupiter4 ,as to ,jupiter we shall continue our former assumption that a body with four times the effectiveness of that planet1 which here means with twice as great a radius1 would disturb the sun enough to cause glaciation4 ,it would produce about twenty times the electrostatic effect which now appears to be associated with the difference in ,jupiter's effect at maximum and minimum4 ,the temperature of ,jupiter must also be taken into account4 ,the planet is supposed to be hot because its density is low1 being only about #a4be that of water4 ,nevertheless1 it is probably not luminous1 for as ,moulton#aag puts it1 shadows upon it are black and its moons show no sign of illumination except from the sun4 ,hence a temperature of about #fjj deg4,c41 or approximately #ijj deg4 on the absolute scale1 seems to be the highest that can reasonably be assigned to the cold outer layer whence electrons are emitted4 ,as to the temperature of the sun1 we shall adopt the common estimate of about #fcjj deg4,c4 on the absolute scale4 ,the other stars will be taken as averaging the same1 although of course they vary greatly4 ,when ,jeans' method of calculating the probability of a mutual approach of the sun and a star is applied to the assumptions given above1 the results are as shown in ,table #e4 ,on that basis the dark stars seem to be of negligible importance so far as the electrical hypothesis is concerned4 ,even though they may be ten times as numerous as the bright ones there appears to be only one chance in #acj billion years that one of them will approach the sun closely enough to cause the assumed disturbance of the solar atmosphere4 ,on the other hand1 if all the visible stars were the size of the sun1 and as hot as that body1 their electrical effect would be fourfold that of our assumed dark star because of their size1 and #bdja times as great because of their temperature1 or approximately #aj1jjj times as great4 ,under such conditions the theoretical chance of an approach that would cause glaciation is one in #acj million years4 ,if the average visible star is somewhat cooler than the sun and has a radius about two and one-half times as great1 as appears to be the fact1 the chances rise to one in thirty-eight million years4 ,a slight and wholly reasonable change in our assumptions would reduce this last figure to only five or ten million4 ,for instance1 the earth's mean temperature during the glacial period has been assumed as #aj deg4,c4 lower than now1 but the difference may have been only #f deg44 ,again1 the temperature of the outer atmosphere of ,jupiter where the electrons are shot out may be only #ejj deg4 or #gjj deg4 absolute1 instead of #ijj deg44 ,or the diameter of the average star may be five or ten times that of the sun1 instead of only two and one-half times as great4 ,all this1 however1 may for the present be disregarded4 ,the essential point is that even when the assumptions err on the side of conservatism1 the results are of an order of magnitude which puts the electrical hypothesis within the bounds of possibility1 whereas similar assumptions put the tidal hypothesis1 with its single approach in twelve billion years1 far beyond those limits4 ,the figures for ,betelgeuse in ,table #e are interesting4 ,at a meeting of the ,american ,association for the ,advancement of ,science in ,december1 #aibj1 ,michelson reported that by measurements of the interference of light coming from the two sides of that bright star in ,orion1 the observers at ,mount ,wilson had confirmed the recent estimates of three other authorities that the star's diameter is about #bah million miles1 or #bej times that of the sun4 ,if other stars so much surpass the estimates of only a decade or two ago1 the average diameter of all the visible stars must be many times that of the sun4 ,the low figure for ,betelgeuse in section ,d of the table means that if all the stars were as large as ,betelgeuse1 several might often be near enough to cause profound disturbances of the solar atmosphere4 ,nevertheless1 because of the low temperature of the giant red stars of the ,betelgeuse type1 the distance at which one of them would produce a given electrical effect is only about five times the distance at which our assumed average star would produce the same effect4 ,this1 to be sure1 is on the assumption that the radiation of energy from incandescent bodies varies according to temperature in the same ratio as the radiation from black bodies4 ,even if this assumption departs somewhat from the truth1 it still seems almost certain that the lower temperature of the red compared with the high temperature of the white stars must to a considerable degree reduce the difference in electrical effect which would otherwise arise from their size4 ,,table #e ,,theoretical ,,probability ,,of ,,stellar ,,approaches ---------------------------------------- ----------------------------- #a #b #c #d ,average ,dark ,stars ,sun ,star ,betelgeuse ---------------------------------------- ----------------------------- ,a4 ,approximate radius in miles #dcj1jjj #hfj1jjj #b1aej1jjjbah1jjj1jjj ,b4 ,assumed temperature above absolute zero4 #ijj deg4 ,c4 #fcjj deg4 ,c4 #edjj deg4 ,c4 #caej deg4 ,c4 ,c4 ,approximate theoretical distance at which star would cause solar disturbance great enough to cause glaciation 7billions#aah of miles74 #a4b #abj #bbj #cbjj ,d4 ,average interval between approaches close enough to cause glaciation if all stars #acj1jjj1jjj1jjj were of given #aai type4 ,years4 #acj1jjj1jjjch1jjj1jjj #gjj1jjj ---------------------------------------- ----------------------------- ,thus far in our attempt to estimate the distance at which a star might disturb the sun enough to cause glaciation on the earth1 we have considered only the star's size and temperature4 ,no account has been taken of the degree to which its atmosphere is disturbed4 ,yet in the case of the sun this seems to be one of the most important factors4 ,the magnetic field of sunspots is sometimes #ej or #ajj times as strong as that of the sun in general4 ,the strength of the magnetic field appears to depend on the strength of the electrical currents in the solar atmosphere4 ,but the intensity of the sunspots and1 by inference1 of the electrical currents1 may depend on the electrical action of ,jupiter and the other planets4 ,if we apply a similar line of reasoning to the stars1 we are at once led to question whether the electrical activity of double stars may not be enormously greater than that of isolated stars like the sun4 ,if this line of reasoning is correct1 the atmosphere of every double star must be in a state of commotion vastly greater than that of the sun's atmosphere even when it is most disturbed4 ,for example1 suppose the sun were accompanied by a companion of equal size at a distance of one million miles1 which would make it much like many known double stars4 ,suppose also that in accordance with the general laws of physics the electrical effect of the two suns upon one another is proportional to the fourth power of the temperature1 the square of the radius1 and the inverse square of the distance4 ,then the effect of each sun upon the other would be sixty billion 7#f x #ajaj7 times as great as the present electrical effect of ,jupiter upon the sun4 ,just what this would mean as to the net effect of a pair of such suns upon the electrical potential of other bodies at a distance we can only conjecture4 ,the outstanding fact is that the electrical conditions of a double star must be radically different and vastly more intense than those of a single star like the sun4 ,this conclusion carries weighty consequences4 ,at present twenty or more stars are known to be located within about #ajj trillion miles of the sun 7five parsecs1 as the astronomers say71 or #af4e light years4 ,according to the assumptions employed in ,table #e an average single star would influence the sun enough to cause glaciation if it came within approximately #bjj billion miles4 ,if the star were double1 however1 it might have an electrical capacity enormously greater than that of the sun4 ,then it would be able to cause glaciation at a correspondingly great distance4 ,today ,alpha ,centauri1 the nearest known star about twenty-five trillion miles1 or #d4c light years from the sun1 and ,sirius1 the brightest star in the heavens1 is about fifty trillion miles away1 or #h4e light years4 ,if these stars were single and had a diameter three times that of the sun1 and if they were of the same temperature as has been assumed for ,betelgeuse1 which is about fifty times as far away as ,alpha ,centauri1 the relative effects of the three stars upon the sun would be1 approximately1 ,betelgeuse #gjj1 ,alpha ,centauri #bej1 ,sirius #a4 ,but ,alpha ,centauri is triple and ,sirius double1 and both are much hotter than ,betelgeuse4 ,hence ,alpha ,centauri and even ,sirius may be far more effective than ,betelgeuse4 ,the two main components of ,alpha ,centauri are separated by an average distance of about #b1bjj1jjj1jjj miles1 or somewhat less than that of ,neptune from the sun4 ,a third and far fainter star1 one of the faintest yet measured1 revolves around them at a great distance4 ,in mass and brightness the two main components are about like the sun1 and we will assume that the same is true of their radius4 ,then1 according to the assumptions made above1 their effect in disturbing one another electrically would be about #aj1jjj times the total effect of ,jupiter upon the sun1 or #bejj times the effect that we have assumed to be necessary to produce a glacial period4 ,we have already seen in ,table #e that1 according to our assumptions1 a single star like the sun would have to approach within #abj billion miles of the solar system1 or within #b per cent of a light year1 in order to cause glaciation4 ,by a similar process of reasoning it appears that if the mutual electrical excitation of the two main parts of ,alpha ,centauri1 regardless of the third part1 is proportional to the apparent excitation of the sun by ,jupiter1 ,alpha ,centauri would be #ejjj times as effective as the sun4 ,in other words1 if it came within #h1ejj1jjj1jjj1jjj miles of the sun1 or #a4d light years1 it would so change the electrical conditions as to produce a glacial epoch4 ,in that case ,alpha ,centauri is now so near that it introduces a disturbing effect equal to about one-sixth of the effect needed to cause glaciation on the earth4 ,sirius and perhaps others of the nearer and brighter or larger stars may also create appreciable disturbances in the electrical condition of the sun's atmosphere1 and may have done so to a much greater degree in the past1 or be destined to do so in the future4 ,thus an electrical hypothesis of solar disturbances seems to indicate that the position of the sun in respect to other stars may be a factor of great importance in determining the earth's climate4 ,,footnotes3 ,footnote #aab3 ,h4 ,h4 ,turner3 ,on a ,long ,period in ,chinese ,earthquake ,records2 ,mon4 ,not4 ,royal ,astron4 ,soc41 ,vol4 #gi1 #aiai1 pp4 #eca-eci2 ,vol4 #hj1 #aibj1 pp4 #fag-fai2 ,long ,period ,terms in the ,growth of ,trees2 idem1 pp4#gic-hjh4 ,footnote #aac3 ,harlow ,shapley3 ,note on a ,possible ,factor in ,geologic ,climates2 ,jour4 ,geol41 ,vol4 #bi1 ,no4 #d1 ,may1 #aiba2 ,novae and ,variable ,stars1 ,pub4 ,astron4 ,soc4 ,pac41 ,no4 #aid1 ,aug41 #aiba4 ,footnote #aad3 ,j4 ,h4 ,jeans3 ,problems of ,cosmogony and ,stellar ,dynamics1 ,cambridge1 #aiai4 ,footnote #aae3 ,this fact is so important and at the same time so surprising to the layman1 that a quotation from ,the ,electron ,theory of ,matter by ,o4 ,w4 ,richardson1 #aiad1 pp4 #cbf and #ccd is here added4 ,it is a very familiar fact that when material bodies are heated they emit electromagnetic radiations1 in the form of thermal1 luminous1 and actinic rays1 in appreciable quantities4 ,such an effect is a natural consequence of the electron and kinetic theories of matter4 ,on the kinetic theory1 temperature is a measure of the violence of the motion of the ultimate particles2 and we have seen that on the electron theory1 electromagnetic radiation is a consequence of their acceleration4 ,the calculation of this emission from the standpoint of the electron theory alone is a very complex problem which takes us deeply into the structure of matter and which has probably not yet been satisfactorily resolved4 ,fortunately1 we can find out a great deal about these phenomena by the application of general principles like the conservation of energy and the second law of thermodynamics without considering special assumptions about the ultimate constitution of matter4 ,it is to be borne in mind that the emission under consideration occurs at all temperatures although it is more marked the higher the temperature4444 ,the energy per unit volume1 in vacuo1 of the radiation in equilibrium in an enclosure at the absolute temperature1 ,t1 is equal to a universal constant1 ,a1 multiplied by the fourth power of the absolute temperature4 ,since the intensity of the radiation is equal to the energy per unit volume multiplied by the velocity of light1 it follows that the former must also be proportional to the fourth power of the absolute temperature4 ,moreover1 if ,e is the total emission from unit area of a perfectly black body1 we see from p4 #ccj that ,e,a',t#d1 where ,a' is a new universal constant4 ,this result is usually known as ,stefan's ,law4 ,it was suggested by ,stefan in the inaccurate form that the total radiant energy of emission from bodies varies as the fourth power of the absolute temperature1 as a generalization from the results of experiments4 ,the credit for showing that it is a consequence of the existence of radiation pressure combined with the principles of thermodynamics is due to ,bartoli and ,boltzmann4 ,footnote #aaf3 ,quoted by ,moulton in his ,introduction to ,astronomy4 ,footnote #aag3 ,introduction to ,astronomy4 ,footnote #aah3 ,the term billions1 here and elsewhere1 is used in the ,american sense1 #aji4 ,footnote #aai3 ,the assumed number of stars here is ten times as great as in the other parts of this line4 ,,chapter ,,xv ,,the ,,sun',s ,,journey ,,through ,,space ,having gained some idea of the nature of the electrical hypothesis of solar disturbances and of the possible effect of other bodies upon the sun's atmosphere1 let us now compare the astronomical data with those of geology4 ,let us take up five chief points for which the geologist demands an explanation1 and which any hypothesis must meet if it is to be permanently accepted4 ,these are 7#a7 the irregular intervals at which glacial periods occur2 7#b7 the division of glacial periods into epochs separated sometimes by hundreds of thousands of years2 7#c7 the length of glacial periods and epochs2 7#d7 the occurrence of glacial stages and historic pulsations in the form of small climatic waves superposed upon the larger waves of glacial epochs2 7#e7 the occurrence of climatic conditions much milder than those of today1 not only in the middle portion of the great geological eras1 but even in some of the recent inter-glacial epochs4 #a4 ,the irregular duration of the interval from one glacial epoch to another corresponds with the irregular distribution of the stars4 ,if glaciation is indirectly due to stellar influences1 the epochs might fall close together1 or might be far apart4 ,if the average interval were ten million years1 one interval might be thirty million or more and the next only one or two hundred thousand4 ,according to ,schuchert1 the known periods of glacial or semi-glacial climate have been approximately as follows3 ,,list ,,of ,,glacial ,,periods #a4 ,archeozoic4 7#a_/d of geological time or perhaps much more7 ,no known glacial periods4 #b4 ,proterozoic4 7#a_/d of geological time7 a4 ,oldest known glacial period near base of ,proterozoic in ,canada4 ,evidence widely distributed4 b4 ,indian glacial period2 time unknown4 c4 ,african glacial period2 time unknown4 d4 ,glaciation near end of ,proterozoic in ,australia1 ,norway1 and ,china4 #c4 ,paleozoic4 7#a_/d of geological time7 a4 ,late ,ordovician7874 ,local in ,arctic ,norway4 b4 ,silurian4 ,local in ,alaska4 c4 ,early ,devonian4 ,local in ,south ,africa4 d4 ,early ,permian4 ,world-wide and very severe4 #d4 ,mesozoic and ,cenozoic4 7#a_/d of geological time7 a-b4 ,none definitely determined during ,mesozoic1 although there appears to have been periods of cooling 7a7 in the late ,triassic1 and 7b7 in the late ,cretacic1 with at least local glaciation in early ,eocene4 c4 ,severe glacial period during ,pleistocene4 ,this table suggests an interesting inquiry4 ,during the last few decades there has been great interest in ancient glaciation and geologists have carefully examined rocks of all ages for signs of glacial deposits4 ,in spite of the large parts of the earth which are covered with deposits belonging to the ,mesozoic and ,cenozoic1 which form the last quarter of geological time1 the only signs of actual glaciation are those of the great ,pleistocene period and a few local occurrences at the end of the ,mesozoic or beginning of the ,cenozoic4 ,late in the ,triassic and early in the ,jurassic1 the climate appears to have been rigorous1 although no tillites have been found to demonstrate glaciation4 ,in the preceding quarter1 that is1 the ,paleozoic1 the ,permian glaciation was more severe than that of the ,pleistocene1 and the ,devonian than that of the ,eocene1 while the ,ordovician evidences of low temperature are stronger than those at the end of the ,triassic4 ,in view of the fact that rocks of ,paleozoic age cover much smaller areas than do those of later age1 the three ,paleozoic glaciations seem to indicate a relative frequency of glaciation4 ,going back to the ,proterozoic1 it is astonishing to find that evidence of two highly developed glacial periods1 and possibly four1 has been discovered4 ,since the ,indian and the ,african glaciations of ,proterozoic times are as yet undated1 we cannot be sure that they are not of the same date as the others4 ,nevertheless1 even two is a surprising number1 for not only are most ,proterozoic rocks so metamorphosed that possible evidences of glacial origin are destroyed1 but rocks of that age occupy far smaller areas than either those of ,paleozoic or1 still more1 ,mesozoic and ,cenozoic age4 ,thus the record of the last three-quarters of geological time suggests that if rocks of all ages were as abundant and as easily studied as those of the later periods1 the frequency of glacial periods would be found to increase as one goes backward toward the beginnings of the earth's history4 ,this is interesting1 for ,jeans holds that the chances that the stars would approach one another were probably greater in the past than at present4 ,this conclusion is based on the assumption that our universe is like the spiral nebulae in which the orbits of the various members are nearly circular during the younger stages4 ,jeans considers it certain that in such cases the orbits will gradually become larger and more elliptical because of the attraction of one body for another4 ,thus as time goes on the stars will be more widely distributed and the chances of approach will diminish4 ,if this is correct1 the agreement between astronomical theory and geological conclusions suggests that the two are at least not in opposition4 ,the first quarter of geological time as well as the last three must be considered in this connection4 ,during the ,archeozoic1 no evidence of glaciation has yet been discovered4 ,this suggests that the geological facts disprove the astronomical theory4 ,but our knowledge of early geological times is extremely limited1 so limited that lack of evidence of glaciation in the ,archeozoic may have no significance4 ,archeozoic rocks have been studied minutely over a very small percentage of the earth's land surface4 ,moreover1 they are highly metamorphosed so that1 even if glacial tills existed1 it would be hard to recognize them4 ,third1 according to both the nebular and the planetesimal hypotheses1 it seems possible that during the earliest stages of geological history the earth's interior was somewhat warmer than now1 and the surface may have been warmed more than at present by conduction1 by lava flows1 and by the fall of meteorites4 ,if the earth during the ,archeozoic period emitted enough heat to raise its surface temperature a few degrees1 the heat would not prevent the development of low forms of life but might effectively prevent all glaciation4 ,this does not mean that it would prevent changes of climate1 but merely changes so extreme that their record would be preserved by means of ice4 ,it will be most interesting to see whether future investigations in geology and astronomy indicate either a semi-uniform distribution of glacial periods throughout the past1 or a more or less regular decrease in frequency from early times down to the present4 #b4 ,the ,pleistocene glacial period was divided into at least four epochs1 while in the ,permian at least one inter-glacial epoch seems certain1 and in some places the alternation between glacial and non-glacial beds suggests no less than nine4 ,in the other glaciations the evidence is not yet clear4 ,the question of periodicity is so important that it overthrows most glacial hypotheses4 ,indeed1 had their authors known the facts as established in recent years1 most of the hypotheses would never have been advanced4 ,the carbon dioxide hypothesis is the only one which was framed with geologically rapid climatic alternations in mind4 ,it certainly explains the facts of periodicity better than does any of its predecessors1 but even so it does not account for the intimate way in which variations of all degrees from those of the weather up to glacial epochs seem to grade into one another4 ,according to our stellar hypothesis1 occasional groups of glacial epochs would be expected to occur close together and to form long glacial periods4 ,this is because many of the stars belong to groups or clusters in which the stars move in parallel paths4 ,a good example is the cluster in the ,hyades1 where ,boss has studied thirty-nine stars with special care4#abj ,the stars are grouped about a center about #acj light years from the sun4 ,the stars themselves are scattered over an area about thirty light years in diameter4 ,they average about the same distance apart as do those near the sun1 but toward the center of the group they are somewhat closer together4 ,the whole thirty-nine sweep forward in essentially parallel paths4 ,boss estimates that #hjj1jjj years ago the cluster was only half as far from the sun as at present1 but probably that was as near as it has been during recent geological times4 ,all of the thirty-nine stars of this cluster1 as ,moulton#aba puts it1 are much greater in light-giving power than the sun4 ,the luminosities of even the five smallest are from five to ten times that of the sun1 while the largest are one hundred times greater in light-giving power than our own luminary4 ,their masses are probably much greater than that of the sun4 ,if the sun were to pass through such a cluster1 first one star and then another might come so near as to cause a profound disturbance in the sun's atmosphere4 #c4 ,another important point upon which a glacial hypothesis may come to grief is the length of the periods or rather of the epochs which compose the periods4 ,during the last or ,pleistocene glacial period the evidence in ,america and ,europe indicates that the inter-glacial epochs varied in length and that the later ones were shorter than the earlier4 ,chamberlin and ,salisbury1 from a comparison of various authorities1 estimate that the intervals from one glacial epoch to another form a declining series1 which may be roughly expressed as follows3 #af-h-d-b-a1 where unity is the interval from the climax of the late ,wisconsin1 or last glacial epoch1 to the present4 ,most authorities estimate the culmination of the late ,wisconsin glaciation as twenty or thirty thousand years ago4 ,penck estimates the length of the last inter-glacial period as #fj1jjj years and the preceding one as #bdj1jjj4abb ,r4 ,t4 ,chamberlin1 as already stated1 finds that the consensus of opinion is that inter-glacial epochs have averaged five times as long as glacial epochs4 ,the actual duration of the various glaciations probably did not vary in so great a ratio as did the intervals from one glaciation to another4 ,the main point1 however1 is the irregularity of the various periods4 ,the relation of the stellar electrical hypothesis to the length of glacial epochs may be estimated from column ,c1 in ,table #e4 ,there we see that the distances at which a star might possibly disturb the sun enough to cause glaciation range all the way from #abj billion miles in the case of a small star like the sun1 to #cbjj billion in the case of ,betelgeuse1 while for double stars the figure may rise a hundred times higher4 ,from this we can calculate how long it would take a star to pass from a point where its influence would first amount to a quarter of the assumed maximum to a similar point on the other side of the sun4 ,in making these calculations we will assume that the relative rate at which the star and the sun approach each other is about twenty-two miles per second1 or #gjj million miles per year1 which is the average rate of motion of all the known stars4 ,according to the distances in ,table #e this gives a range from about #ejj years up to about #aj1jjj1 which might rise to a million in the case of double stars4 ,of course the time might be relatively short if the sun and a rapidly moving star were approaching one another almost directly1 or extremely long if the sun and the star were moving in almost the same direction and at somewhat similar rates1--a condition more common than the other4 ,here1 as in so many other cases1 the essential point is that the figures which we thus obtain seem to be of the right order of magnitude4 #d4 ,post-glacial climatic stages are so well known that in ,europe they have definite names4 ,their sequence has already been discussed in ,chapter ,,xii4 ,fossils found in the peat bogs of ,denmark and ,scandinavia1 for example1 prove that since the final disappearance of the continental ice cap at the close of the ,wisconsin there has been at least one period when the climate of ,europe was distinctly milder than now4 ,directly overlying the sheets of glacial drift laid down by the ice there is a flora corresponding to that of the present tundras4 ,next come remains of a forest vegetation dominated by birches and poplars1 showing that the climate was growing a little warmer4 ,third1 there follow evidences of a still more favorable climate in the form of a forest dominated by pines2 fourth1 one where oak predominates2 and fifth1 a flora similar to that of the ,black ,forest of ,germany1 indicating that in ,scandinavia the temperature was then decidedly higher than today4 ,this fifth flora has retreated southward once more1 having been driven back to its present latitude by a slight recurrence of a cool stormy climate4#abc ,in central ,asia evidence of post-glacial stages is found not only in five distinct moraines but in a corresponding series of elevated strands surrounding salt lakes and of river terraces in non-glaciated arid regions4#abd ,in historic as well as prehistoric times1 as we have already seen1 there have been climatic fluctuations4 ,for instance1 the twelfth or thirteenth century ,b4 ,c4 appears to have been almost as mild as now1 as does the seventh century ,b4 ,c4 ,on the other hand about #ajjj ,b4 ,c41 at the time of ,christ1 and in the fourteenth century there were times of relative severity4 ,thus it appears that both on a large and on a small scale pulsations of climate are the rule4 ,any hypothesis of climatic changes must satisfy the periods of these pulsations4 ,these conditions furnish a problem which makes difficulty for almost all hypotheses of climatic change4 ,according to the present hypothesis1 earth movements such as are discussed in ,chapter ,,xii may cooeperate with two astronomical factors4 ,one is the constant change in the positions of the stars1 a change which we have already called kaleidoscopic1 and the other is the fact that a large proportion of the stars are double or multiple4 ,when one star in a group approaches the sun closely enough to cause a great solar disturbance1 numerous others may approach or recede and have a minor effect4 ,thus1 whenever the sun is near groups of stars we should expect that the earth would show many minor climatic pulsations and stages which might or might not be connected with glaciation4 ,the historic pulsations shown in the curve of tree growth in ,california1 ,fig4 #d1 are the sort of changes that would be expected if movements of the stars have an effect on the solar atmosphere4 ,not only are fully a third of all the visible stars double1 as we have already seen1 but at least a tenth of these are known to be triple or multiple4 ,in many of the double stars the two bodies are close together and revolve so rapidly that whatever periodicity they might create in the sun's atmosphere would be very short4 ,in the triplets1 however1 the third star is ordinarily at least ten times as far from the other two as they are from each other1 and its period of rotation sometimes runs into hundreds or thousands of years4 ,an actual multiple star in the constellation ,polaris will serve as an example4 ,the main star is believed by ,jeans to consist of two parts which are almost in contact and whirl around each other with extraordinary speed in four days4 ,if this is true they must keep each other's atmospheres in a state of intense commotion4 ,much farther away a third star revolves around this pair in twelve years4 ,at a much greater distance a fourth star revolves around the common center of gravity of itself and the other three in a period which may be #bj1jjj years4 ,still more complicated cases probably exist4 ,suppose such a system were to traverse a path where it would exert a perceptible influence on the sun for thirty or forty thousand years4 ,the varying movements of its members would produce an intricate series of cycles which might show all sorts of major and minor variations in length and intensity4 ,thus the varied and irregular stages of glaciation and the pulsations of historic times might be accounted for on the hypothesis of the proximity of the sun to a multiple star1 as well as on that of the less pronounced approach and recession of a number of stars4 ,in addition to all this1 an almost infinitely complex series of climatic changes of long and short duration might arise if the sun passed through a nebula4 #e4 ,we have seen in ,chapter ,,viii that the contrast between the somewhat severe climate of the present and the generally mild climate of the past is one of the great geological problems4 ,the glacial period is not a thing of the distant past4 ,geologists generally recognize that it is still with us4 ,greenland and ,antarctica are both shrouded in ice sheets in latitudes where fossil floras prove that at other periods the climate was as mild as in ,england or even ,new ,zealand4 ,the present glaciated regions1 be it noted1 are on the polar borders of the world's two most stormy oceanic areas1 just where ice would be expected to last longest according to the solar cyclonic hypothesis4 ,in contrast with the semi-glacial conditions of the present1 the last inter-glacial epoch was so mild that not only men but elephants and hippopotamuses flourished in central ,europe1 while at earlier times in the middle of long eras1 such as the ,paleozoic and ,mesozoic1 corals1 cycads1 and tree ferns flourished within the ,arctic circle4 ,if the electro-stellar hypothesis of solar disturbances proves well founded1 it may explain these peculiarities4 ,periods of mild climate would represent a return of the sun and the earth to their normal conditions of quiet4 ,at such times the atmosphere of the sun is assumed to be little disturbed by sunspots1 faculae1 prominences1 and other allied evidences of movements2 and the rice-grain structure is perhaps the most prominent of the solar markings4 ,the earth at such times is supposed to be correspondingly free from cyclonic storms4 ,its winds are then largely of the purely planetary type1 such as trade winds and westerlies4 ,its rainfall also is largely planetary rather than cyclonic4 ,it falls in places such as the heat equator where the air rises under the influence of heat1 or on the windward slopes of mountains1 or in regions where warm winds blow from the ocean over cold lands4 ,according to the electro-stellar hypothesis1 the conditions which prevailed during hundreds of millions of years of mild climate mean merely that the solar system was then in parts of the heavens where stars--especially double stars--were rare or small1 and electrical disturbances correspondingly weak4 ,today1 on the other hand1 the sun is fairly near a number of stars1 many of which are large doubles4 ,hence it is supposed to be disturbed1 although not so much as at the height of the last glacial epoch4 ,after the preceding parts of this book had been written1 the assistance of ,dr4 ,schlesinger made it possible to test the electro-stellar hypothesis by comparing actual astronomical dates with the dates of climatic or solar phenomena4 ,in order to make this possible1 ,dr4 ,schlesinger and his assistants have prepared ,table #f1 giving the position1 magnitude1 and motions of the thirty-eight nearest stars1 and especially the date at which each was nearest the sun4 ,in column #aj where the dates are given1 a minus sign indicates the past and a plus sign the future4 ,dr4 ,shapley has kindly added column #ab1 giving the absolute magnitudes of the stars1 that of the sun being #d4h1 and column #ac1 showing their luminosity or absolute radiation1 that of the sun being unity4 ,finally1 column #ad shows the effective radiation received by the sun from each star when the star is at a minimum distance4 ,unity in this case is the effect of a star like the sun at a distance of one light year4 ,it is well known that radiation of all kinds1 including light1 heat1 and electrical emissions1 varies in direct proportion to the exposed surface1 that is1 as the square of the radius of a sphere1 and inversely as the square of the distance4 ,from black bodies1 as we have seen1 the total radiation varies as the fourth power of the absolute temperature4 ,it is not certain that either light or electrical emissions from incandescent bodies vary in quite this same proportion1 nor is it yet certain whether luminous and electrical emissions vary exactly together4 ,nevertheless they are closely related4 ,since the light coming from each star is accurately measured1 while no information is available as to electrical emissions1 we have followed ,dr4 ,shapley's suggestion and used the luminosity of the stars as the best available measure of total radiation4 ,this is presumably an approximate measure of electrical activity1 provided some allowance be made for disturbances by outside bodies such as companion stars4 ,hence the inclusion of column #ad4 ,,table #f ,,thirty-,,eight ,,stars ,,having ,,largest ,,known ,,parallaxes ,star ,code #a ,groombr4 #cd #b ,greek3 e ,cassiop4 #c #d ,greek3 k ,tucanae #e ,greek3 t ,ceti #f ,greek3 d#b ,eridani #g ,greek3 e ,eridani #h #dj7j7b ,eridani #i ,cordoba ,z4 #bdc #aj ,weisse #eib #aa ,greek3 a ,can4 ,maj4 7,sirius7 #ab ,greek3 a ,can4 ,min4 7,procyon7 #ac ,fedorenko #adeg-h #ad ,groombr4 #afah #ae ,weisse #bcd #af ,lalande #baahe #ag ,lalande #babeh #ah #ai ,lalande #becgb #bj ,greek3 a ,centauri #ba ,greek3 x ,bootes #bb ,lalande #bgagc #bc ,weisse #abei #bd ,lacaille #gaid #be ,greek3 b #daf #bf ,argel -#j4agdae-f #bg ,barnard's star #bh #gjp ,ophiuchi #bi ,greek3 ,s #bcih #cj ,greek3 s ,draconis #ca ,greek3 a ,aquilae 7,altair7 #cb #fa ,cygni #cc ,lacaille #hgfj #cd ,greek3 e ,indi #ce ,krueger #fj #cf ,lacaille #iceb #cg ,lalande #dffej #ch ,c4 ,g4 ,a4 #cbdaf 7 ,double star47 7#a7 7#b7 7#c7 7#d7 7#e7 7#f7 ,right ,declination ,visual ,spectrum ,proper ,radial ,star ,ascension ,greek3 d ,mag4 m ,motion ,velocity code ,greek3 a #aijj km4 per #aijj sec4 ---------------------------------------- -------------------------- #a #j;h #abm4#g #dc deg4#bg' #h4a ,ma #b4hi #c #b #dc 4#j #eg #ag #c4f ,f#h #a 4#bd #aj #c #dc 4#i #d #ee #ab4c ,f#j #c 4#ja 44444 #d #a #ab 4#d -#fi #bd #e4j ,f#h 4#ci #ab #e #ci 4#d -#af #bh #c4f ,k#j #a 4#ib - #af ---------------------------------------- -------------------------- #f #c #ae 4#i -#dc #bg #d4c ,g#e #c 4#af #hg #g #bh 4#b - #i #dh #c4h ,k#j 4#ig #af #h #d #aj 4#g - #g #di #d4e ,g#e #d 4#jh - #db #i #e #g 4#g -#dd #ei #i4b ,k#b #h 4#ge #bdb #aj #bf 4#d - #c #db #h4h ,k#b #b 4#bb 44444 ---------------------------------------- -------------------------- #aa #f #dj 4#g -#af #ce -#a4f ,a#j #a 4#cb - #h #ab #g #cd 4#a #e #bi #j4e ,f#e #a 4#bd - #d #ac #i #g 4#f #ec #g #g4i ,ma #a 4#fh #aj #ad #aj #e 4#c #di #eh #f4h ,k#ep #a 4#de - #cj #ae #ad 4#b #bj #bb #i4j 444 4#di 44444 ---------------------------------------- -------------------------- #af #eg 4#i #cf #ch #g4f ,mb #d 4#gh - #hg #ag #aa #j 4#e #dd #b #h4e ,k#e #d 4#eb #fe #ah #ab 4#j -#eg #b #ab4j 444 #b 4#fi 44444 #ai #ac #dj 4#g #ae #bf #h4e ,k#e #b 4#cj 44444 #bj #ad #cb 4#h -#fj #be #j4b ,g #c 4#fh #bb ---------------------------------------- -------------------------- #ba #ad #df 4#h #ai #ca #d4f ,k#ep 4#ag #d #bb #ea 4#f -#bj #eh #e4h ,kp #a 4#if #bj #bc #af #da 4#d #cc #da #h4d 444 4#cg 44444 #bd #ag #aa 4#e -#df #cb #e4g ,k 4#ig 44444 #be #ab 4#a -#cd #ec #e4i ,k#e #a 4#ai - #d ---------------------------------------- -------------------------- #bf #cg 4#j #fh #bf #i4a ,k #a 4#cc 44444 #bg #eb 4#i #d #be #i4g ,mb #aj 4#cj - #hj #bh #ah #j 4#d #b #ca #d4c ,k #a 4#ac 44444 #bi #da 4#g #ei #bi #h4h ,k #b 4#ca 44444 #cj #ai #cb 4#e #fi #bi #d4h ,g#e #a 4#hd #bf ---------------------------------------- -------------------------- #ca #de 4#i #h #cf #a4b ,a#e 4#ff - #cc #cb #ba #b 4#d #ch #ae #e4f ,k#e #e 4#bj - #fd #cc #aa 4#d -#ci #ae #f4f ,g #c 4#ec #ac #cd #ee 4#g -#eg #ab #d4h ,k#e #d 4#gj - #ci #ce #bb #bd 4#d #eg #ab #i4b 444 4#hg 44444 ---------------------------------------- -------------------------- #cf #ei 4#d -#cf #bf #g4a ,k #f 4#ij #ab #cg #bc #dd 4#j #a #eb #h4g ,ma #a 4#ci 44444 #ch #ei 4#e -#cg #ea #h4b ,g #f 4#je #bf 7#g7 7#i7 7#aa7 7#ac7 7#ad7 ,present ,minimum ,magnitude ,luminosity ,effective ,parallax ,distance at ,min4 ,dist4 radiation ,greek3 p ,light ,yrs4 at minimum 7#h7 7#aj7 7#ab7 distance ,star ,maximum ,time of ,absolute from sun ,code ,parallax ,minimum ,magnitude ,distance ---------------------------------------- ------------------------------- #a 4#bh 4#bh #aa4f -#djjj #h4a #aj4c #j4jjfc #j4jjjjea #b 4#ah 4#ai #ag4a -#dgjjj #c4e #d4i #j4ia #j4jjcaaj #c 4#bd 4444 4444 444444 4444 #ad4b #j4jjjag 44444444 #d 4#af 4#bc #ad4b -#bfdjjj #d4b #f4j #j4cc #j4jjafaj #e 4#cb 4#cg #h4h #dfjjj #c4c #f4a #j4cj #j4jjchdj ---------------------------------------- ------------------------------- #f 4#af 4#bb #ad4h -#ccjjj #c4f #e4c #j4fc #j4jjbifj #g 4#ca 4#df #g4a -#ajfjjj #c4j #f4c #j4be #j4jjdigj #h 4#ba 4#bc #ad4b #aijjj #d4c #f4a #j4cj #j4jjadgj #i 4#cb 4#fh #d4h -#ajjjj #g4f #aa4g #j4jjag #j4jjjjgd #aj 4#ag 4444 4444 444444 4444 #i4i #j4jji 44444444 ---------------------------------------- ------------------------------- #aa 4#cg 4#da #h4j #fejjj -#a4h #a4b #bg4ej #j4dbijjj #ab 4#ca 4#cb #aj4b #cdjjj #j4e #c4j #e4be #j4jeacjj #ac 4#af 4#af #bj4d -#bdjjj #g4i #h4i #j4jbc #j4jjjjee #ad 4#ah 4#bc #ad4b #fijjj #f4c #h4a #j4jdh #j4jjjbch #ae 4#ai 4444 4444 444444 4444 #aj4d #j4jjeg 44444444 ---------------------------------------- ------------------------------- #af 4#da 4#gf #d4c #bjjjj #f4b #aj4g #j4jjdd #j4jjjbch #ag 4#ai 4#bb #ad4h -#bjjjj #h4b #i4i #j4jji #j4jjjjda #ah 4#cd 4444 4444 444444 4444 #ad4g #j4jjjaa 44444444 #ai 4#ai 4444 4444 444444 4444 #i4i #j4jji 44444444 #bj 4#gf #a4jc #c4b -#bhjjj -#j4e #d4f #a4bj #j4aagejj ---------------------------------------- ------------------------------- #ba 4#ag 4#bb #ad4h -#eihjjj #d4j #e4h #j4dj #j4jjahae #bb 4#ah 4#ai #ag4a -#cfjjj #e4f #g4a #j4ab #j4jjjdab #bc 4#ah 4444 4444 444444 4444 #i4g #j4jaa 44444444 #bd 4#ai 4444 4444 444444 4444 #g4a #j4ab 44444444 #be 4#ag 4#ag #ai4b #bajjj #e4g #g4a #j4ab #j4jjjcbi ---------------------------------------- ------------------------------- #bf 4#bb 4444 4444 444444 4444 #aj4h #j4jjd 44444444 #bg 4#ec 4#gj #d4g #ajjjj #i4a #ac4c #j4jjbe #j4jjjaad #bh 4#ai 4444 4444 444444 4444 #e4g #j4dd 44444444 #bi 4#bi 4444 4444 444444 4444 #aa4a #j4jjcj 44444444 #cj 4#bj 4#bc #ad4b -#dijjj #d4e #f4c #j4be #j4jjabch ---------------------------------------- ------------------------------- #ca 4#ba 4#ea #f4d #aagjjj -#j4g #b4h #f4cj #j4aecfjj #cb 4#cj 4#ch #h4f #aijjj #e4a #h4j #j4jec #j4jjjgae #cc 4#be 4#bf #ab4f -#aajjj #f4f #h4f #j4jcj #j4jjjahi #cd 4#bh 4#ca #aj4e #agjjj #d4f #g4j #j4ac #j4jjabcj #ce 4#bf 4444 4444 4444444 4444 #aa4c #j4jjbe 44444444 ---------------------------------------- ------------------------------- #cf 4#bi 4#bi #aa4b -#cjjj #g4a #i4d #j4jad #j4jjjaaa #cg 4#ag 4444 4444 4444444 4444 #i4i #j4jji 44444444 #ch 4#bb 4#bb #ad4h -#gjjj #h4b #i4i #j4jji #j4jjjjda ---------------------------------------- ------------------------------- ,on the basis of column #ad and of the movements and distances of the stars as given in the other columns ,fig4 #aj has been prepared4 ,this gives an estimate of the approximate electrical energy received by the sun from the nearest stars for #gj1jjj years before and after the present4 ,it is based on the twenty-six stars for which complete data are available in ,table #f4 ,the inclusion of the other twelve would not alter the form of the curve1 for even the largest of them would not change any part by more than about half of #a per cent1 if as much4 ,nor would the curve be visibly altered by the omission of all except four of the twenty-six stars actually used4 ,the four that are important1 and their relative luminosity when nearest the sun1 are ,sirius #dbi1jjj1 ,altair #aec1jjj1 ,alpha ,centauri #aag1ejj1 and ,procyon #ea1cjj4 ,the figure for the next star is only #digj1 while for this star combined with the other twenty-one that are unimportant it is only #bd1hej4 ,figure #aj is not carried more than #gj1jjj years into the past or into the future because the stars near the sun at more remote times are not included among the thirty-eight having the largest known parallaxes4 ,that is1 they have either moved away or are not yet near enough to be included4 ,indeed1 as ,dr4 ,schlesinger strongly emphasizes1 there may be swiftly moving1 bright or gigantic stars which are now quite far away1 but whose inclusion would alter ,fig4 #aj even within the limits of the #adj1jjj years there shown4 ,it is almost certain1 however1 that the most that these would do would be to raise1 but not obliterate1 the minima on either side of the main maximum4 ,illustration3 ,fig4 #aj4 ,climatic changes of #adj1jjj years as inferred from the stars4 ,in preparing ,fig4 #aj it has been necessary to make allowance for double stars4 ,passing by the twenty-two unimportant stars1 it appears that the companion of ,sirius is eight or ten magnitudes smaller than that star1 while the companions of ,procyon and ,altair are five or more magnitudes smaller than their bright comrades4 ,this means that the luminosity of the faint components is at most only #a per cent of that of their bright companions and in the case of ,sirius not a hundredth of #a per cent4 ,hence their inclusion would have no visible effect on ,fig4 #aj4 ,in ,alpha ,centauri1 on the other hand1 the two components are of almost the same magnitude4 ,for this reason the effective radiation of that star as given in column #ad is doubled in ,fig4 #aj1 while for another reason it is raised still more4 ,the other reason is that if our inferences as to the electrical effect of the sun on the earth and of the planets on the sun are correct1 double stars1 as we have seen1 must be much more effective electrically than single stars4 ,by the same reasoning two bright stars close together must excite one another much more than a bright star and a very faint one1 even if the distances in both cases are the same4 ,so1 too1 other things being equal1 a triple star must be more excited electrically than a double star4 ,hence in preparing ,fig4 #aj all double stars receive double weight and each part of ,alpha ,centauri receives an additional #ej per cent because both parts are bright and because they have a third companion to help in exciting them4 ,according to the electro-stellar hypothesis1 ,alpha ,centauri is more important climatically than any other star in the heavens not only because it is triple and bright1 but because it is the nearest of all stars1 and moves fairly rapidly4 ,sirius and ,procyon move slowly in respect to the sun1 only about eleven and eight kilometers per second respectively1 and their distances at minimum are fairly large1 that is1 #h and #aj4b light years4 ,hence their effect on the sun changes slowly4 ,altair moves faster1 about twenty-six kilometers per second1 and its minimum distance is #f4d light years1 so that its effect changes fairly rapidly4 ,alpha ,centauri moves about twenty-four kilometers per second1 and its minimum distance is only #c4b light years4 ,hence its effect changes very rapidly1 the change in its apparent luminosity as seen from the sun amounting at maximum to about #cj per cent in #aj1jjj years against #ad per cent for ,altair1 #d for ,sirius1 and #b for ,procyon4 ,the vast majority of the stars change so much more slowly than even ,procyon that their effect is almost uniform4 ,all the stars at a distance of more than perhaps twenty or thirty light years may be regarded as sending to the sun a practically unchanging amount of radiation4 ,it is the bright stars within this limit which are important1 and their importance increases with their proximity1 their speed of motion1 and the brightness and number of their companions4 ,hence ,alpha ,centauri causes the main maximum in ,fig4 #aj1 while ,sirius1 ,altair1 and ,procyon combine to cause a general rise of the curve from the past to the future4 ,let us now interpret ,fig4 #aj geologically4 ,the low position of the curve fifty to seventy thousand years ago suggests a mild inter-glacial climate distinctly less severe than that of the present4 ,geologists say that such was the case4 ,the curve suggests a glacial epoch culminating about #bh1jjj years ago4 ,the best authorities put the climax of the last glacial epoch between twenty-five and thirty thousand years ago4 ,the curve shows an amelioration of climate since that time1 although it suggests that there is still considerable severity4 ,the retreat of the ice from ,north ,america and ,europe1 and its persistence in ,greenland and ,antarctica agree with this4 ,and the curve indicates that the change of climate is still persisting1 a conclusion in harmony with the evidence as to historic changes4 ,if ,alpha ,centauri is really so important1 the effect of its variations1 provided it has any1 ought perhaps to be evident in the sun4 ,the activity of the star's atmosphere presumably varies1 for the orbits of the two components have an eccentricity of #j4ea4 ,hence during their period of revolution1 #ha4b years1 the distance between them ranges from #a1ajj1jjj1jjj to #c1cjj1jjj1jjj miles4 ,they were at a minimum distance in #achh1 #adei1 #aeej1 #afca1 #agac1 #agid1 #ahge1 and will be again in #aief4 ,in ,fig4 #aa1 showing sunspot variations1 it is noticeable that the years #agid and #ahge come just at the ends of periods of unusual solar activity1 as indicated by the heavy horizontal line4 ,a similar period of great activity seems to have begun about #aiad4 ,if its duration equals the average of its two predecessors1 it will end about #aiej4 ,back in the fourteenth century a period of excessive solar activity1 which has already been described1 culminated from #acgj to #ache1 or just before the two parts of ,alpha ,centauri were at a minimum distance4 ,thus in three and perhaps four cases the sun has been unusually active during a time when the two parts of the star were most rapidly approaching each other and when their atmospheres were presumably most disturbed and their electrical emanations strongest4 ,illustration3 ,fig4 #aa4 ,sunspot curve showing cycles1 #agej to #aibj4 ,note4 ,the asterisks indicate two absolute minima of sunspots in #ahaj and #aiac1 and the middle years 7#aghj and #ahed7 of two periods when the sunspot maxima never fell below #ie4 ,if ,alpha ,centauri has an effect on the sun's atmosphere1 the end of another such period would be expected not far from #aieg4 ,the fact that ,alpha ,centauri1 the star which would be expected most strongly to influence the sun1 and hence the earth1 was nearest the sun at the climax of the last glacial epoch1 and that today the solar atmosphere is most active when the star is presumably most disturbed may be of no significance4 ,it is given for what it is worth4 ,its importance lies not in the fact that it proves anything but that no contradiction is found when we test the electro-stellar hypothesis by facts which were not thought of when the hypothesis was framed4 ,a vast amount of astronomical work is still needed before the matter can be brought to any definite conclusion4 ,in case the hypothesis stands firm1 it may be possible to use the stars as a help in determining the exact chronology of the later part of geological times4 ,if the hypothesis is disproved1 it will merely leave the question of solar variations where it is today4 ,it will not influence the main conclusions of this book as to the causes and nature of climatic changes4 ,its value lies in the fact that it calls attention to new lines of research4 ,,footnotes3 ,footnote #abj3 ,lewis ,boss3 ,convergent of a ,moving ,cluster in ,taurus2 ,astronom4 ,jour41 ,vol4 #bf1 ,no4 #d1 #aijh1 pp4 #ca-cf4 ,footnote #aba3 ,f4 ,r4 ,moulton3 in ,introduction to ,astronomy1 #aiaf4 ,footnote #abb3 ,a4 ,penck3 ,die ,alpen im ,eiszeitalter1 ,leipzig1 #aiji4 ,footnote #abc3 ,r4 ,d4 ,salisbury3 ,physical ,geography of the ,pleistocene1 in ,outlines of ,geologic ,history1 by ,willis and ,salisbury1 #aiaj1 pp4 #bgc-bgd4 ,footnote #abd3 ,davis1 ,pumpelly1 and ,huntington3 ,explorations in ,turkestan1 ,carnegie ,inst4 of ,wash41 ,no4 #bf1 #aije4 ,in ,north ,america the stages have been the subject of intensive studies on the part of ,taylor1 ,leverett1 ,goldthwait1 and many others4 ,,chapter ,,xvi ,,the ,,earth',s ,,crust ,,and ,,the ,,sun ,although the problems of this book may lead far afield1 they ultimately bring us back to the earth and to the present4 ,several times in the preceding pages there has been mention of the fact that periods of extreme climatic fluctuations are closely associated with great movements of the earth's crust whereby mountains are uplifted and continents upheaved4 ,in attempting to explain this association the general tendency has been to look largely at the past instead of the present4 ,hence it has been almost impossible to choose among three possibilities1 all beset with difficulties4 ,first1 the movements of the crust may have caused the climatic fluctuations2 second1 climatic changes may cause crustal movements2 and third1 variations in solar activity or in some other outside agency may give rise to both types of terrestrial phenomena4 ,the idea that movements of the earth's crust are the main cause of geological changes of climate is becoming increasingly untenable as the complexity and rapidity of climatic changes become more clear1 especially during post-glacial times4 ,it implies that the earth's surface moves up and down with a speed and facility which appear to be out of the question4 ,if volcanic activity be invoked the problem becomes no clearer4 ,even if volcanic dust should fill the air frequently and completely1 neither its presence nor absence would produce such peculiar features as the localization of glaciers1 the distribution of loess1 and the mild climate of most parts of geological time4 ,nevertheless1 because of the great difficulties presented by the other two possibilities many geologists still hold that directly or indirectly the greater climatic changes have been mainly due to movements of the earth's crust and to the reaction of the crustal movements on the atmosphere4 ,the possibility that climatic changes are in themselves a cause of movements of the earth's crust seems so improbable that no one appears to have investigated it with any seriousness4 ,nevertheless1 it is worth while to raise the question whether climatic extremes may cooeperate with other agencies in setting the time when the earth's crust shall be deformed4 ,as to the third possibility1 it is perfectly logical to ascribe both climatic changes and crustal deformation to some outside agency1 solar or otherwise1 but hitherto there has been so little evidence on this point that such an ascription has merely begged the question4 ,if heavenly bodies should approach the earth closely enough so that their gravitational stresses caused crustal deformation1 all life would presumably be destroyed4 ,as to the sun1 there has hitherto been no conclusive evidence that it is related to crustal movements1 although various writers have made suggestions along this line4 ,in this chapter we shall carry these suggestions further and shall see that they are at least worthy of study4 ,as a preliminary to this study it may be well to note that the coincidence between movements of the earth's crust and climatic changes is not so absolute as is sometimes supposed4 ,for example1 the profound crustal changes at the end of the ,mesozoic were not accompanied by widespread glaciation so far as is yet known1 although the temperature appears to have been lowered4 ,nor was the violent volcanic and diastrophic activity in the ,miocene associated with extreme climates4 ,indeed1 there appears to have been little contrast from zone to zone1 for figs1 bread fruit trees1 tree ferns1 and other plants of low latitudes grew in ,greenland4 ,nevertheless1 both at the end of the ,mesozoic and in the ,miocene the climate may possibly have been severe for a time1 although the record is lost4 ,on the other hand1 ,kirk's recent discovery of glacial till in ,alaska between beds carrying an undoubted ,middle ,silurian fauna indicates glaciation at a time when there was little movement of the crust so far as yet appears4#abe ,thus we conclude that while climatic changes and crustal movements usually occur together1 they may occur separately4 ,according to the solar-cyclonic hypothesis such a condition is to be expected4 ,if the sun were especially active when the terrestrial conditions prohibited glaciation1 changes of climate would still occur1 but they would be milder than under other circumstances1 and would leave little record in the rocks4 ,or there might be glaciation in high latitudes1 such as that of southern ,alaska in the ,middle ,silurian1 and none elsewhere4 ,on the other hand1 when the sun was so inactive that no great storminess occurred1 the upheaval of continents and the building of mountains might go on without the formation of ice sheets1 as apparently happened at the end of the ,mesozoic4 ,the lack of absolute coincidence between glaciation and periods of widespread emergence of the lands is evident even today1 for there is no reason to suppose that the lands are notably lower or less extensive now than they were during the ,pleistocene glaciation4 ,in fact1 there is much evidence that many areas have risen since that time4 ,yet glaciation is now far less extensive than in the ,pleistocene4 ,any attempt to explain this difference on the basis of terrestrial changes is extremely difficult1 for the shape and altitude of continents and mountains have not changed much in twenty or thirty thousand years4 ,yet the present moderately mild epoch1 like the puzzling inter-glacial epochs of earlier times1 is easily explicable on the assumption that the sun's atmosphere may sometimes vary in harmony with crustal activity1 but does not necessarily do so at all times4 ,turning now to the main problem of how climatic changes may be connected with movements of the earth's crust1 let us follow our usual method and examine what is happening today4 ,let us first inquire whether earthquakes1 which are one of the chief evidences that crustal movements are actually taking place in our own times1 show any connection with sunspots4 ,in order to test this1 we have compared ,milne's ,catalogue of ,destructive ,earthquakes from #ahjj to #ahii1 with ,wolf's sunspot numbers for the same period month by month4 ,the earthquake catalogue1 as its compiler describes it1 is an attempt to give a list of earthquakes which have announced changes of geological importance in the earth's crust2 movements which have probably resulted in the creation or the extension of a line of fault1 the vibrations accompanying which could1 with proper instruments1 have been recorded over a continent or the whole surface of our world4 ,small earthquakes have been excluded1 while the number of large earthquakes both for ancient and modern times has been extended4 ,as an illustration of exclusion1 ,i may mention that between #ahjj and #ahjh1 which are years taken at random1 ,i find in ,mallet's catalogue #djg entries4 ,only thirty-seven of these1 which were accompanied by structural damage1 have been retained4 ,other catalogues such as those of ,perry and ,fuchs have been treated similarly4#abf ,if the earthquakes in such a carefully selected list bear a distinct relation to sunspots1 it is at least possible and perhaps probable that a similar relation may exist between solar activity and geological changes in the earth's crust4 ,the result of the comparison of earthquakes and sunspots is shown in ,table #g4 ,the first column gives the sunspot numbers2 the second1 the number of months that had the respective spot numbers during the century from #ahjj to #ahii4 ,column ,c shows the total number of earthquakes during the months having any particular degree of spottedness2 while ,d1 which is the significant column1 gives the average number of destructive earthquakes per month under each of the six conditions of solar spottedness4 ,the regularity of column ,d is so great as to make it almost certain that we are here dealing with a real relationship4 ,column ,f1 which shows the average number of earthquakes in the month succeeding any given condition of the sun1 is still more regular except for the last entry4 ,,table #g ,,destructive ,,earthquakes ,,from #ahjj ,,to #ahii ,,compared ,,with ,,sunspots ,a3 ,sunspot numbers ,b3 ,number of months per ,wolf's ,table ,c3 ,number of earthquakes ,d3 ,average number of earthquakes per month ,e3 ,number of earthquakes in succeeding month ,f3 ,average number of earthquakes in succeeding month ,a ,b ,c ,d ,e ,f #j-ae #cdd #ebb #a4eb #eab #a4di #ae-cj #aid #cjf #a4eh #caj #a4fj #cj-ej #bcg #dcc #a4hc #dci #a4he #ej-gj #aie #djb #b4jf #cij #b4jj #gj-ajj #ace #bhf #b4ab #caj #b4cj over #ajj #ie #bah #b4cj #age #a4hd ,the chance that six numbers taken at random will arrange themselves in any given order is one in #gbj4 ,in other words1 there is one chance in #gbj that the regularity of column ,d is accidental4 ,but column ,f is as regular as column ,d except for the last entry4 ,if columns ,d and ,e were independent there would be one chance in about #ejj1jjj that the six numbers in both columns would fall in the same order1 and one chance in #ad1djj that five numbers in each would fall in the same order4 ,but the two columns are somewhat related1 for although the after-shocks of a great earthquake are never included in ,milne's table1 a world-shaking earthquake in one region during a given month probably creates conditions that favor similar earthquakes elsewhere during the next month4 ,hence the probability that we are dealing with a purely accidental arrangement in ,table #g is less than one in #ad1djj and greater than one in #ejj1jjj4 ,it may be one in #bj1jjj or #ajj1jjj4 ,in any event it is so slight that there is high probability that directly or indirectly sunspots and earthquakes are somehow connected4 ,in ascertaining the relation between sunspots and earthquakes it would be well if we could employ the strict method of correlation coefficients4 ,this1 however1 is impossible for the entire century1 for the record is by no means homogeneous4 ,the earlier decades are represented by only about one-fourth as many earthquakes as the later ones1 a condition which is presumably due to lack of information4 ,this makes no difference with the method employed in ,table #g1 since years with many and few sunspots are distributed almost equally throughout the entire nineteenth century1 but it renders the method of correlation coefficients inapplicable4 ,during the period from #ahej onward the record is much more nearly homogeneous1 though not completely so4 ,even in these later decades1 however1 allowance must be made for the fact that there are more earthquakes in winter than in summer1 the average number per month for the fifty years being as follows3 ,jan4 #b4h ,may #b4d ,sept4 #b4e ,feb4 #b4d ,june #b4c ,oct4 #b4f ,mar4 #b4e ,july #b4d ,nov4 #b4g ,apr4 #b4d ,aug4 #b4d ,dec4 #b4h ,the correlation coefficient between the departures from these monthly averages and the corresponding departures from the monthly averages of the sunspots for the same period1 #ahej-ahii1 are as follows3 ,sunspots and earthquakes of same month3 #j4jdb1 or #a4e times the probable error4 ,sunspots of a given month and earthquakes of that month and the next3 #j4jhd1 or #c4a times the probable error4 ,sunspots of three consecutive months and earthquakes of three consecutive months allowing a lag of one month1 i4e41 sunspots of ,january1 ,february1 and ,march compared with earthquakes of ,february1 ,march1 and ,april2 sunspots of ,february1 ,march1 and ,april with earthquakes of ,march1 ,april1 and ,may1 etc42 #j4aab1 or #d4a times the probable error4 ,these coefficients are all small1 but the number of individual cases1 #fjj months1 is so large that the probable error is greatly reduced1 being only -#j4jbg or -#j4jbh4 ,moreover1 the nature of our data is such that even if there is a strong connection between solar changes and earth movements1 we should not expect a large correlation coefficient4 ,in the first place1 as already mentioned1 the earthquake data are not strictly homogeneous4 ,second1 an average of about two and one-half strong earthquakes per month is at best only a most imperfect indication of the actual movement of the earth's crust4 ,third1 the sunspots are only a partial and imperfect measure of the activity of the sun's atmosphere4 ,fourth1 the relation between solar activity and earthquakes is almost certainly indirect4 ,in view of all these conditions1 the regularity of ,table #g and the fact that the most important correlation coefficient rises to more than four times the probable error makes it almost certain that the solar and terrestrial phenomena are really connected4 ,we are now confronted by the perplexing question of how this connection can take place4 ,thus far only three possibilities present themselves1 and each is open to objections4 ,the chief agencies concerned in these three possibilities are heat1 electricity1 and atmospheric pressure4 ,heat may be dismissed very briefly4 ,we have seen that the earth's surface becomes relatively cool when the sun is active4 ,theoretically even the slightest change in the temperature of the earth's surface must influence the thermal gradient far into the interior and hence cause a change of volume which might cause movements of the crust4 ,practically the heat of the surface ceases to be of appreciable importance at a depth of perhaps twenty feet1 and even at that depth it does not act quickly enough to cause the relatively prompt response which seems to be characteristic of earthquakes in respect to the sun4 ,the second possibility is based on the relationship between solar and terrestrial electricity4 ,when the sun is active the earth's atmospheric electrical potential is subject to slight variations4 ,it is well known that when two opposing points of an ionized solution are oppositely charged electrically1 a current passes through the liquid and sets up electrolysis whereby there is a segregation of materials1 and a consequent change in the volume of the parts near the respective electrical poles4 ,the same process takes place1 although less freely1 in a hot mass such as forms the interior of the earth4 ,the question arises whether internal electrical currents may not pass between the two oppositely charged poles of the earth1 or even between the great continental masses and the regions of heavier rock which underlie the oceans4 ,could this lead to electrolysis1 hence to differentiation in volume1 and thus to movements of the earth's crust8 ,could the results vary in harmony with the sun8 ,bowie#abg has shown that numerous measurements of the strength and direction of the earth's gravitative pull are explicable only on the assumption that the upheaval of a continent or a mountain range is due in part not merely to pressure1 or even to flowage of the rocks beneath the crust1 but also to an actual change in volume whereby the rocks beneath the continent attain relatively great volume and those under the oceans a small volume in proportion to their weight4 ,the query arises whether this change of volume may be related to electrical currents at some depth below the earth's surface4 ,the objections to this hypothesis are numerous4 ,first1 there is little evidence of electrolytic differentiation in the rocks4 ,second1 the outer part of the earth's crust is a very poor conductor so that it is doubtful whether even a high degree of electrification of the surface would have much effect on the interior4 ,third1 electrolysis due to any such mild causes as we have here postulated must be an extremely slow process1 too slow1 presumably1 to have any appreciable result within a month or two4 ,other objections join with these three in making it seem improbable that the sun's electrical activity has any direct effect upon movements of the earth's crust4 ,the third1 or meteorological hypothesis1 which makes barometric pressure the main intermediary between solar activity and earthquakes1 seems at first sight almost as improbable as the thermal and electrical hypotheses4 ,nevertheless1 it has a certain degree of observational support of a kind which is wholly lacking in the other two cases4 ,among the extensive writings on the periodicity of earthquakes one main fact stands out with great distinctness3 earthquakes vary in number according to the season4 ,this fact has already been shown incidentally in the table of earthquake frequency by months4 ,if allowance is made for the fact that ,february is a short month1 there is a regular decrease in the frequency of severe earthquakes from ,december and ,january to ,june4 ,since most of ,milne's earthquakes occurred in the northern hemisphere1 this means that severe earthquakes occur in winter about #bj per cent oftener than in summer4 ,the most thorough investigation of this subject seems to have been that of ,davisson4#abh ,his results have been worked over and amplified by ,knott1#abi who has tested them by ,schuster's exact mathematical methods4 ,his results are given in ,table #h4acj ,here the northern hemisphere is placed first2 then come the ,east ,indies and the ,malay ,archipelago lying close to the equator2 and finally the southern hemisphere4 ,in the northern hemisphere practically all the maxima come in the winter1 for the month of ,december appears in fifteen cases out of the twenty-five in column ,d1 while ,january1 ,february1 or ,november appears in six others4 ,it is also noticeable that in sixteen cases out of twenty-five the ratio of the actual to the expected amplitude in column ,g is four or more1 so that a real relationship is indicated1 while the ratio falls below three only in ,japan and ,zante4 ,the equatorial data1 unlike those of the northern hemisphere1 are indefinite1 for in the ,east ,indies no month shows a marked maximum and the expected amplitude exceeds the actual amplitude4 ,even in the ,malay ,archipelago1 which shows a maximum in ,may1 the ratio of actual to expected amplitude is only #b4f4 ,turning to the southern hemisphere1 the winter months of that hemisphere are as strongly marked by a maximum as are the winter months of the northern hemisphere4 ,july or ,august appears in five out of six cases4 ,here the ratio between the actual and expected amplitudes is not so great as in the northern hemisphere4 ,nevertheless1 it is practically four in ,chile1 and exceeds five in ,peru and ,bolivia1 and in the data for the entire southern hemisphere4 ,,table #h ,,seasonal ,,march ,,of ,,earthquakes ,,after ,,davisson ,,and ,,knott ,a3 ,region ,b3 ,limiting ,dates ,c3 ,number of ,shocks ,d3 ,maximum ,month ,e3 ,amplitude ,f3 ,expected ,amplitude ,g3 ,ratio of ,actual to ,expected ,amplitude ,a ,b ,c ,d ,e ,f ,g ,northern ,hemisphere #bbc-ahej #ehgi ,dec4 #j4aaj #j4jbc #d4h ,northern ,hemisphere #ahfe-ahhd #hacc ,dec4 #j4bij #j4jbj #ad4e ,europe #ahfe-ahhd #edii ,dec4 #j4cej #j4jbd #ad4f ,europe #cjf-ahdc #aifa ,dec4 #j4bbj #j4jdj #e4e ,southeast ,europe #ahei-ahhg #cdgj ,dec4 #j4baj #j4jcj #g4j ,vesuvius ,district #ahfe-ahhc #eac ,dec4 #j4bej #j4jgh #c4b ,italy3 ,old ,tromometre #ahgb-ahhg #fagcb ,dec4 #j4dij #j4jjg #gj4j ,old ,tromometre #ahgf-ahhg #chedf ,dec4 #j4dfj #j4jji #di4e ,normal ,tromometre #ahgf-ahhg #chedf ,dec4 #j4dij #j4jji #eb4h ,balkan1 etc4 #ahfe-ahhd #fbd ,dec4 #j4bgj #j4jga #c4h ,hungary1 etc4 #ahfe-ahhd #chd ,dec4 #j4caj #j4jij #c4d ,italy #ahfe-ahhc #bcej ,dec47,sept47#j4adj #j4jcg #c4h ,grecian ,archip4 #ahei-ahha #cegh ,dec4-,jan4 #j4afd #j4jcj #e4e ,austria #ahfe-ahhd #dfa ,jan4 #j4cgj #j4jhc #d4d ,switzerland1 etc4 #ahfe-ahhc #ebd ,jan4 #j4efj #j4jgg #g4c ,asia #ahfe-ahhd #deh ,feb4 #j4ccj #j4jhc #d4j ,north ,america #ahfe-ahhd #eeb ,nov4 #j4cej #j4jge #d4g ,california #ahej-ahhf #idi ,oct4 #j4cjj #j4jeh #e4b ,japan #ahgh-ahha #bdf ,dec4 #j4dfj #j4aac #d4a ,japan #ahgb-ahhj #cfg ,dec4-,jan4 #j4bef #j4jic #b4h ,japan #ahgf-ahia #aajd ,feb4 #j4aij #j4jec #c4f ,japan #ahhe-ahhi #biig ,oct4 #j4jhj #j4jcb #b4e ,zante #ahbe-ahfc #acbf ,aug4 #j4ajj #j4jdi #b4j ,italy1 ,north #ahfe-ahhc #aeac ,sept47,nov47 #j4baj #j4jdf #d4f of ,naples ,east ,indies #ahgc-ahha #eae ,aug41 ,oct41 #j4jga8 #j4jgh #j4i or ,dec48 ,malay ,archip4 #ahfe-ahhd #eih ,may #j4aij #j4jgb #b4f ,new ,zealand #ahfi-ahgi #ehe ,aug4-,sept4 #j4bjc #j4jgc #b4h ,chile #ahgc-ahha #bab ,july #j4dhj #j4abb #c4i ,southern ,hemisphere #ahfe-ahhd #gea ,july #j4cgj #j4jfe #e4g ,new ,zealand #ahfh-ahij #fda ,march1 ,may #j4jej #j4jgj #j4g ,chile #ahfe-ahhc8 #caf ,july1 ,dec4 #j4bgj #j4ajj #b4g ,peru1 ,bolivia #ahfe-ahhd #cej ,july #j4dhj #j4jie #e4a ,the whole relationship between earthquakes and the seasons in the northern and southern hemispheres is summed up in ,fig4 #ab taken from ,knott4 ,the northern hemisphere shows a regular diminution in earthquake frequency from ,december until ,june1 and an increase the rest of the year4 ,in the southern hemisphere the course of events is the same so far as summer and winter are concerned1 for ,august with its maximum comes in winter1 while ,february with its minimum comes in summer4 ,in the southern hemisphere the winter month of greatest seismic activity has over #ajj per cent more earthquakes than the summer month of least activity4 ,in the northern hemisphere this difference is about #hj per cent1 but this smaller figure occurs partly because the northern data include certain interesting and significant regions like ,japan and ,china where the usual conditions are reversed4#aca ,if equatorial regions were included in ,fig4 #ab1 they would give an almost straight line4 ,the connection between earthquakes and the seasons is so strong that almost no students of seismology question it1 although they do not agree as to its cause4 ,a meteorological hypothesis seems to be the only logical explanation4#acb ,wherever sufficient data are available1 earthquakes appear to be most numerous when climatic conditions cause the earth's surface to be most heavily loaded or to change its load most rapidly4 ,the main factor in the loading is apparently atmospheric pressure4 ,this acts in two ways4 ,first1 when the continents become cold in winter the pressure increases4 ,on an average the air at sea level presses upon the earth's surface at the rate of #ad4g pounds per square inch1 or over a ton per square foot1 and only a little short of thirty million tons per square mile4 ,an average difference of one inch between the atmospheric pressure of summer and winter over ten million square miles of the continent of ,asia1 for example1 means that the continent's load in winter is about ten million million tons heavier than in summer4 ,second1 the changes in atmospheric pressure due to the passage of storms are relatively sharp and sudden4 ,hence they are probably more effective than the variations in the load from season to season4 ,this is suggested by the rapidity with which the terrestrial response seems to follow the supposed solar cause of earthquakes4 ,it is also suggested by the fact that violent storms are frequently followed by violent earthquakes4 ,earthquake weather1 as ,dr4 ,schlesinger suggests1 is a common phrase in the typhoon region of ,japan1 ,china1 and the ,east ,indies4 ,during tropical hurricanes a change of pressure amounting to half an inch in two hours is common4 ,on ,september #bb1 #ahhe1 at ,false ,point ,lighthouse on the ,bay of ,bengal1 the barometer fell about an inch in six hours1 then nearly an inch and a half in not much over two hours1 and finally rose fully two inches inside of two hours4 ,a drop of two inches in barometric pressure means that a load of about two million tons is removed from each square mile of land2 the corresponding rise of pressure means the addition of a similar load4 ,such a storm1 and to a less degree every other storm1 strikes a blow upon the earth's surface1 first by removing millions of tons of pressure and then by putting them on again4#acc ,such storms1 as we have seen1 are much more frequent and severe when sunspots are numerous than at other times4 ,moreover1 as ,veeder#acd long ago showed1 one of the most noteworthy evidences of a connection between sunspots and the weather is a sudden increase of pressure in certain widely separated high pressure areas4 ,in most parts of the world winter is not only the season of highest pressure and of most frequent changes of ,veeder's type1 but also of severest storms4 ,hence a meteorological hypothesis would lead to the expectation that earthquakes would occur more frequently in winter than in summer4 ,on the ,chinese coast1 however1 and also on the oceanic side of ,japan1 as well as in some more tropical regions1 the chief storms come in summer in the form of typhoons4 ,these are the places where earthquakes also are most abundant in summer4 ,thus1 wherever we turn1 storms and the related barometric changes seem to be most frequent and severe at the very times when earthquakes are also most frequent4 ,illustration3 ,fig4 #ab4 ,seasonal distribution of earthquakes4 7,after ,davisson and ,knott47 solid line ---- ,northern ,hemisphere4 dashed line 4444 ,southern ,hemisphere4 ,other meteorological factors1 such as rain1 snow1 winds1 and currents1 probably have some effect on earthquakes through their ability to load the earth's crust4 ,the coming of vegetation may also help4 ,these agencies1 however1 appear to be of small importance compared with the storms4 ,in high latitudes and in regions of abundant storminess most of these factors generally combine with barometric pressure to produce frequent changes in the load of the earth's crust1 especially in winter4 ,in low latitudes1 on the other hand1 there are few severe storms1 and relatively little contrast in pressure and vegetation from season to season2 there is no snow2 and the amount of ground water changes little4 ,with this goes the twofold fact that there is no marked seasonal distribution of earthquakes1 and that except in certain local volcanic areas1 earthquakes appear to be rare4 ,in proportion to the areas concerned1 for example1 there is little evidence of earthquakes in equatorial ,africa and ,south ,america4 ,the question of the reality of the connection between meteorological conditions and crustal movements is so important that every possible test should be applied4 ,at the suggestion of ,professor ,schlesinger we have looked up a very ingenious line of inquiry4 ,during the last decades of the nineteenth century1 a long series of extremely accurate observations of latitude disclosed a fact which had previously been suspected but not demonstrated1 namely1 that the earth wabbles a little about its axis4 ,the axis itself always points in the same direction1 and since the earth slides irregularly around it the latitude of all parts of the earth keeps changing4 ,chandler has shown that the wabbling thus induced consists of two parts4 ,the first is a movement in a circle with a radius of about fifteen feet which is described in approximately #dcj days4 ,this so-called ,eulerian movement is a normal gyroscopic motion like the slow gyration of a spinning top4 ,this depends on purely astronomical causes1 and no terrestrial cause can stop it or eliminate it4 ,the period appears to be constant1 but there are certain puzzling irregularities4 ,the usual amplitude of this movement1 as ,schlesinger#ace puts it1 is about #j4bg1 but twice in recent years it has jumped to #j4dj4 ,such a change could be accounted for by supposing that the earth had received a severe blow or a series of milder blows tending in the same direction4 ,these blows1 which were originally suggested by ,helmert are most interesting in view of our suggestion as to the blows struck by storms4 ,the second movement of the pole has a period of a year1 and is roughly an ellipse whose longest radius is fourteen feet and the shortest1 four feet2 or1 to put it technically1 there is an annual term with a maximum amplitude of about #j4bj4 ,this1 however1 varies irregularly4 ,the result is that the pole seems to wander over the earth's surface in the spiral fashion illustrated in ,fig4 #ac4 ,it was early suggested that this peculiar wandering of the pole in an annual period must be due to meteorological causes4 ,jeffreys#acf has investigated the matter exhaustively4 ,he assumes certain reasonable values for the weight of air added or subtracted from different parts of the earth's surface according to the seasons4 ,he also considers the effect of precipitation1 vegetation1 and polar ice1 and of variations of temperature and atmospheric pressure in their relation to movements of the ocean4 ,then he proceeds to compare all these with the actual wandering of the pole from #aijg to #aiac4 ,while it is as yet too early to say that any special movement of the pole was due to the specific meteorological conditions of any particular year1 ,jeffreys' work makes it clear that meteorological causes1 especially atmospheric pressure1 are sufficient to cause the observed irregular wanderings4 ,slight wanderings may arise from various other sources such as movements of the rocks when geological faults occur or the rush of a great wave due to a submarine earthquake4 ,so far as known1 however1 all these other agencies cause insignificant displacements compared with those arising from movements of the air4 ,this fact coupled with the mathematical certainty that meteorological phenomena must produce some wandering of the pole1 has caused most astronomers to accept ,jeffreys' conclusion4 ,if we follow their example we are led to conclude that changes in atmospheric pressure and in the other meteorological conditions strike blows which sometimes shift the earth several feet from its normal position in respect to the axis4 ,illustration3 ,fig4 #ac4 ,wandering of the pole from #ahij to #ahih4 7,after ,moulton47 ,if the foregoing reasoning is correct1 the great and especially the sudden departures from the smooth gyroscopic circle described by the pole in the ,eulerian motion would be expected to occur at about the same time as unusual earthquake activity4 ,this brings us to an interesting inquiry carried out by ,milne#acg and amplified by ,knott4#ach ,taking ,albrecht's representation of the irregular spiral-like motion of the pole1 as given in ,fig4 #ac1 they show that there is a preponderance of severe earthquakes at times when the direction of motion of the earth in reference to its axis departs from the smooth ,eulerian curve4 ,a summary of their results is given in ,table #i4 ,the table indicates that during the period from #ahib to #aije there were nine different times when the curve of ,fig4 #ac changed its direction or was deflected by less than #aj deg4 during a tenth of a year4 ,in other words1 during those periods it did not curve as much as it ought according to the ,eulerian movement4 ,at such times there were #agi world-shaking earthquakes1 or an average of about #ai4i per tenth of a year4 ,according to the other lines of ,table #i1 in thirty-two cases the deflection during a tenth of a year was between #aj deg4 and #be deg41 while in fifty-six cases it was from #be deg4 to #dj deg44 ,during these periods the curve remained close to the ,eulerian path and the world-shaking earthquakes averaged only #h4b and #ab4i4 ,then1 when the deflection was high1 that is1 when meteorological conditions threw the earth far out of its ,eulerian course1 the earthquakes were again numerous1 the number rising to #bc4d when the deflection amounted to more than #ee deg44 ,,table #i ,,deflection ,,of ,,path ,,of ,,pole ,,compared ,,with ,,earthquakes ,no4 of ,no4 of ,average ,no4 ,deflection ,deflections ,earthquakes of ,earthquakes #j-aj deg4 #i #agi #ai4i #aj-be deg4 #cb #bfc #h4b #be-dj deg4 #ef #gbb #ab4i #dj-ee deg4 #ai #cff #ai4c over #ee deg4 #g #afd #bc4d ,in order to test this conclusion in another way we have followed a suggestion of ,professor ,schlesinger4 ,under his advice the ,eulerian motion has been eliminated and a new series of earthquake records has been compared with the remaining motions of the poles which presumably arise largely from meteorological causes4 ,for this purpose use has been made of the very full records of earthquakes published under the auspices of the ,international ,seismological ,commission for the years #aijc to #aijh1 the only years for which they are available4 ,these include every known shock of every description which was either recorded by seismographs or by direct observation in any part of the world4 ,each shock is given the same weight1 no matter what its violence or how closely it follows another4 ,the angle of deflection has been measured as ,milne measured it1 but since the ,eulerian motion is eliminated1 our zero is approximately the normal condition which would prevail if there were no meteorological complications4 ,dividing the deflections into six equal groups according to the size of the angle1 we get the result shown in ,table #aj4 ,,table #aj ,,earthquakes ,,in #aijc-aijh ,,compared ,,with ,,departures ,,of ,,the ,,projected ,,curve ,,of ,,the ,,earth',s ,,axis ,,from ,,the ,,eulerian ,,position ,average angle of deflection ,average daily number 7#aj periods of #a_/aj year each7 of earthquakes -#aj4e deg4 #h4ca #aa4e deg4 #h4ce #be4h deg4 #h4bc #dj4b deg4 #h4ad #ed4g deg4 #h4hf #ij4c deg4 #aa4ha ,here where some twenty thousand earthquakes are employed the result agrees closely with that of ,milne for a different series of years and for a much smaller number of earthquakes4 ,so long as the path of the pole departs less than about #de deg4 from the smooth gyroscopic ,eulerian path1 the number of earthquakes is almost constant1 about eight and a quarter per day4 ,when the angle becomes large1 however1 the number increases by nearly #ej per cent4 ,thus the work of ,milne1 ,knott1 and ,jeffreys is confirmed by a new investigation4 ,apparently earthquakes and crustal movements are somehow related to sudden changes in the load imposed on the earth's crust by meteorological conditions4 ,this conclusion is quite as surprising to the authors as to the reader--perhaps more so4 ,at the beginning of this investigation we had no faith whatever in any important relation between climate and earthquakes4 ,at its end we are inclined to believe that the relation is close and important4 ,it must not be supposed1 however1 that meteorological conditions are the cause of earthquakes and of movements of the earth's crust4 ,even though the load that the climatic agencies can impose upon the earth's crust runs into millions of tons per square mile1 it is a trifle compared with what the crust is able to support4 ,there is1 however1 a great difference between the cause and the occasion of a phenomenon4 ,suppose that a thick sheet of glass is placed under an increasing strain4 ,if the strain is applied slowly enough1 even so rigid a material as glass will ultimately bend rather than break4 ,but suppose that while the tension is high the glass is tapped4 ,a gentle tap may be followed by a tiny crack4 ,a series of little taps may be the signal for small cracks to spread in every direction4 ,a few slightly harder taps may cause the whole sheet to break suddenly into many pieces4 ,yet even the hardest tap may be the merest trifle compared with the strong force which is keeping the glass in a state of strain and which would ultimately bend it if given time4 ,the earth as a whole appears to stand between steel and glass in rigidity4 ,it is a matter of common observation that rocks stand high in this respect and in the consequent difficulty with which they can be bent without breaking4 ,because of the earth's contraction the crust endures a constant strain1 which must gradually become enormous4 ,this strain is increased by the fact that sediment is transferred from the lands to the borders of the sea and there forms areas of thick accumulation4 ,from this has arisen the doctrine of isostasy1 or of the equalization of crustal pressure4 ,an important illustration of this is the oceanward and equatorial creep which has been described in ,chapter ,,xi4 ,there we saw that when the lands have once been raised to high levels or when a shortening of the earth's axis by contraction has increased the oceanic bulge at the equator1 or when the reverse has happened because of tidal retardation1 the outer part of the earth appears to creep slowly back toward a position of perfect isostatic adjustment4 ,if the sun had no influence upon the earth1 either direct or indirect1 isostasy and other terrestrial processes might flex the earth's crust so gradually that changes in the form and height of the lands would always take place slowly1 even from the geological point of view4 ,thus erosion would usually be able to remove the rocks as rapidly as they were domed above the general level4 ,if this happened1 mountains would be rare or unknown1 and hence climatic contrasts would be far less marked than is actually the case on our earth where crustal movements have repeatedly been rapid enough to produce mountains4 ,nature's methods rarely allow so gradual an adjustment to the forces of isostasy4 ,while the crust is under a strain1 not only because of contraction1 but because of changes in its load through the transference of sediments and the slow increase or decrease in the bulge at the equator1 the atmosphere more or less persistently carries on the tapping process4 ,the violence of that process varies greatly1 and the variations depend largely on the severity of the climatic contrasts4 ,if the main outlines of the cyclonic hypothesis are reliable1 one of the first effects of a disturbance of the sun's atmosphere is increased storminess upon the earth4 ,this is accompanied by increased intensity in almost every meteorological process4 ,the most important effect1 however1 so far as the earth's crust is concerned would apparently be the rapid and intense changes of atmospheric pressure which would arise from the swift passage of one severe storm after another4 ,each storm would be a little tap on the tensely strained crust4 ,any single tap might be of little consequence1 even though it involved a change of a billion tons in the pressure on an area no larger than the state of ,rhode ,island4 ,yet a rapid and irregular succession of such taps might possibly cause the crust to crack1 and finally to collapse in response to stresses arising from the shrinkage of the earth4 ,another and perhaps more important effect of variations in storminess and especially in the location of the stormy areas would be an acceleration of erosion in some places and a retardation elsewhere4 ,a great increase in rainfall may almost denude the slopes of soil1 while a diminution to the point where much of the vegetation dies off has a similar effect4 ,if such changes should take place rapidly1 great thicknesses of sediment might be concentrated in certain areas in a short time1 thus disturbing the isostatic adjustment of the earth's crust4 ,this might set up a state of strain which would ultimately have to be relieved1 thus perhaps initiating profound crustal movements4 ,changes in the load of the earth's crust due to erosion and the deposition of sediment1 no matter how rapid they may be from the geological standpoint1 are slow compared with those due to changes in barometric pressure4 ,a drop of an inch in barometric pressure is equivalent to the removal of about five inches of solid rock4 ,even under the most favorable circumstances1 the removal of an average depth of five inches of rock or its equivalent in soil over millions of square miles would probably take several hundred years1 while the removal of a similar load of air might occur in half a day or even a few hours4 ,thus the erosion and deposition due to climatic variations presumably play their part in crustal deformation chiefly by producing crustal stresses1 while the storms1 as it were1 strike sharp1 sudden blows4 ,suppose now that a prolonged period of world-wide mild climate1 such as is described in ,chapter ,x1 should permit an enormous accumulation of stresses due to contraction and tidal retardation4 ,suppose that then a sudden change of climate should produce a rapid shifting of the deep soil that had accumulated on the lands1 with a corresponding localization and increase in strains4 ,suppose also that frequent and severe storms play their part1 whether great or small1 by producing an intensive tapping of the crust4 ,in such a case the ultimate collapse would be correspondingly great1 as would be evident in the succeeding geological epoch4 ,the sea floor might sink lower1 the continents might be elevated1 and mountain ranges might be shoved up along lines of special weakness4 ,this is the story of the geological period as known to historical geology4 ,the force that causes such movements would be the pull of gravity upon the crust surrounding the earth's shrinking interior4 ,nevertheless climatic changes might occasionally set the date when the gravitative pull would finally overcome inertia1 and thus usher in the crustal movements that close old geologic periods and inaugurate new ones4 ,this1 however1 could occur only if the crust were under sufficient strain4 ,as ,lawson#aci says in his discussion of the elastic rebound theory1 the sudden shifts of the crust which seem to be the underlying cause of earthquakes can occur only after the accumulation of strain to a limit and 444 this accumulation involves a slow creep of the region affected4 ,in the long periods between great earthquakes the energy necessary for such shocks is being stored up in the rocks as elastic compression4 ,if a period of intense storminess should occur when the earth as a whole was in such a state of strain1 the sudden release of the strains might lead to terrestrial changes which would alter the climate still further1 making it more extreme1 and perhaps permitting the storminess due to the solar disturbances to bring about glaciation4 ,at the same time if volcanic activity should increase it would add its quota to the tendency toward glaciation4 ,nevertheless1 it might easily happen that a very considerable amount of crustal movement would take place without causing a continental ice sheet or even a marked alpine ice sheet4 ,or again1 if the strains in the earth's crust had already been largely released through other agencies before the stormy period began1 the climate might become severe enough to cause glaciation in high latitudes without leading to any very marked movements of the earth's crust1 as apparently happened in the ,mid-,silurian period4 ,,footnotes3 ,footnote #abe3 ,e4 ,kirk3 ,paleozoic ,glaciation in ,alaska2 ,am4 ,jour4 ,sci41 #aiah1 p4 #eaa4 ,footnote #abf3 ,j4 ,milne3 ,catalogue of ,destructive ,earthquakes2 ,rep4 ,brit4 ,asso4 ,adv4 ,sci41 #aiaa4 ,footnote #abg3 ,wm4 ,bowie3 ,lecture before the ,geological ,club of ,yale ,university4 ,see ,am4 ,jour4 ,sci41 #aiba4 ,footnote #abh3 ,chas4 ,davisson3 ,on the ,annual and ,semi-annual ,seismic ,periods2 ,roy4 ,soc4 of ,london1 ,philosophical ,transactions1 ,vol4 #ahd1 #ahic1 #aajg ff4 ,footnote #abi3 ,c4 ,g4 ,knott3 ,the ,physics of ,earthquake ,phenomena1 ,oxford1 #aijh4 ,footnote #acj3 ,in ,table #h the first column indicates the region2 the second1 the dates2 and the third1 the number of shocks4 ,the fourth column gives the month in which the annual maximum occurs when the crude figures are smoothed by the use of overlapping six-monthly means4 ,in other words1 the average for each successive six months has been placed in the middle of the period4 ,thus the average of ,january to ,june1 inclusive1 is placed between ,march and ,april1 that for ,february to ,july between ,april and ,may1 and so on4 ,this method eliminates the minor fluctuations and also all periodicities having a duration of less than a year4 ,if there were no annual periodicity the smoothing would result in practically the same figure for each month4 ,the column marked ,amplitude gives the range from the highest month to the lowest divided by the number of earthquakes and then corrected according to ,schuster's method which is well known to mathematicians1 but which is so confusing to the layman that it will not be described4 ,next1 in the column marked ,expected ,amplitude1 we have the amplitude that would be expected if a series of numbers corresponding to the earthquake numbers and having a similar range were arranged in accidental order throughout the year4 ,this also is calculated by ,schuster's method in which the expected amplitude is equal to the square root of pi divided by the number of shocks4 ,when the actual amplitude is four or more times the expected amplitude1 the probability that there is a real periodicity in the observed phenomena becomes so great that we may regard it as practically certain4 ,if there is no periodicity the two are equal4 ,the last column gives the number of times by which the actual exceeds the expected amplitude1 and thus is a measure of the probability that earthquakes vary systematically in a period of a year4 ,footnote #aca3 ,n4 ,f4 ,drake3 ,destructive ,earthquakes in ,china2 ,bull4 ,seism4 ,soc4 ,am41 ,vol4 #b1 #aiab1 pp4 #dj-ia1 #abd-acc4 ,footnote #acb3 ,the only other explanation that seems to have any standing is the psychological hypothesis of ,montessus de ,ballore as given in ,les ,tremblements de ,terre4 ,he attributes the apparent seasonal variation in earthquakes to the fact that in winter people are within doors1 and hence notice movements of the earth much more than in summer when they are out of doors4 ,there is a similar difference between people's habits in high latitudes and low4 ,undoubtedly this does have a marked effect upon the degree to which minor earthquake shocks are noticed4 ,nevertheless1 de ,ballore's contention1 as well as any other psychological explanation1 is completely upset by two facts3 ,first1 instrumental records show the same seasonal distribution as do records based on direct observation1 and instruments certainly are not influenced by the seasons4 ,second1 in some places1 notably ,china1 as ,drake has shown1 the summer rather than the winter is very decidedly the time when earthquakes are most frequent4 ,footnote #acc3 ,a comparison of tropical hurricanes with earthquakes is interesting4 ,taking all the hurricanes recorded in ,august1 ,september1 and ,october1 from #ahhj to #ahii1 and the corresponding earthquakes in ,milne's catalogue1 the correlation coefficient between hurricanes and earthquakes is #j4bcf1 with a probable error of -#j4jhb1 the month being used as the unit4 ,this is not a large correlation1 yet when it is remembered that the hurricanes represent only a small part of the atmospheric disturbances in any given month1 it suggests that with fuller data the correlation might be large4 ,footnote #acd3 ,ellsworth ,huntington3 ,the ,geographic ,work of ,dr4 ,m4 ,a4 ,veeder2 ,geog4 ,rev41 ,vol4 #c1 ,march and ,april1 #aiag1 ,nos4 #c and #d4 ,footnote #ace3 ,frank ,schlesinger3 ,variations of ,latitude2 ,their ,bearing upon ,our ,knowledge of the ,interior of the ,earth2 ,proc4 ,am4 ,phil4 ,soc41 ,vol4 #ed1 #aiae1 pp4 #cea-ceh4 ,also ,smithsonian ,report for #aiaf1 pp4 #bdh-bed4 ,footnote #acf3 ,harold ,jeffreys3 ,causes ,contributory to the ,annual ,variations of ,latitude2 ,monthly ,notices1 ,royal ,astronomical ,soc41 ,vol4 #gf1 #aiaf1 pp4 #dii-ebe4 ,footnote #acg3 ,john ,milne3 ,british ,association ,reports for #aijc and #aijf4 ,footnote #ach3 ,c4 ,g4 ,knott3 ,the ,physics of ,earthquake ,phenomena1 ,oxford1 #aijh4 ,footnote #aci3 ,a4 ,c4 ,lawson3 ,the ,mobility of the ,coast ,ranges of ,california2 ,univ4 of ,calif4 ,pub41 ,geology1 ,vol4 #ab1 ,no4 #g1 pp4 #dca-dgc4 ,,conclusion ,here we must bring this study of the earth's evolution to a close4 ,its fundamental principle has been that the present1 if rightly understood1 affords a full key to the past4 ,with this as a guide we have touched on many hypotheses1 some essential and some unessential to the general line of thought4 ,the first main hypothesis is that the earth's present climatic variations are correlated with changes in the solar atmosphere4 ,this is the keynote of the whole book4 ,it is so well established1 however1 that it ranks as a theory rather than as an hypothesis4 ,next comes the hypothesis that variations in the solar atmosphere influence the earth's climate chiefly by causing variations not only in temperature but also in atmospheric pressure and thus in storminess1 wind1 and rainfall4 ,this1 too1 is one of the essential foundations on which the rest of the book is built1 but though this cyclonic hypothesis is still a matter of discussion1 it seems to be based on strong evidence4 ,these two hypotheses might lead us astray were they not balanced by another4 ,this other is that many climatic conditions are due to purely terrestrial causes1 such as the form and altitude of the lands1 the degree to which the continents are united1 the movement of ocean currents1 the activity of volcanoes1 and the composition of the atmosphere and the ocean4 ,only by combining the solar and the terrestrial can the truth be perceived4 ,finally1 the last main hypothesis of this book holds that if the climatic conditions which now prevail at times of solar activity were magnified sufficiently and if they occurred in conjunction with certain important terrestrial conditions of which there is good evidence1 they would produce most of the notable phenomena of glacial periods4 ,for example1 they would explain such puzzling conditions as the localization and periodicity of glaciation1 the formation of loess1 and the occurrence of glaciation in low latitudes during ,permian and ,proterozoic times4 ,the converse of this is that if the conditions which now prevail at times when the sun is relatively inactive should be intensified1 that is1 if the sun's atmosphere should become calmer than now1 and if the proper terrestrial conditions of topographic form and atmospheric composition should prevail1 there would arise the mild climatic conditions which appear to have prevailed during the greater part of geological time4 ,in short1 there seems thus far to be no phase of the climate of the past which is not in harmony with an hypothesis which combines into a single unit the three main hypotheses of this book1 solar1 cyclonic1 and terrestrial4 ,outside the main line of thought lie several other hypotheses4 ,several of these1 as well as some of the main hypotheses1 are discussed chiefly in ,earth and ,sun1 but as they are given a practical application in this book they deserve a place in this final summary4 ,each of these secondary hypotheses is in its way important4 ,yet any or all may prove untrue without altering our main conclusions4 ,this point cannot be too strongly emphasized1 for there is always danger that differences of opinion as to minor hypotheses and even as to details may divert attention from the main point4 ,among the non-essential hypotheses is the idea that the sun's atmosphere influences that of the earth electrically as well as thermally4 ,this idea is still so new that it has only just entered the stage of active discussion1 and naturally the weight of opinion is against it4 ,although not necessary to the main purpose of this book1 it plays a minor role in the chapter dealing with the relation of the sun to other astronomical bodies4 ,it also has a vital bearing on the further advance of the science of meteorology and the art of weather forecasting4 ,another secondary hypothesis holds that sunspots are set in motion by the planets4 ,whether the effect is gravitational or more probably electrical1 or perhaps of some other sort1 does not concern us at present1 although the weight of evidence seems to point toward electronic emissions4 ,this question1 like that of the relative parts played by heat and electricity in terrestrial climatic changes1 can be set aside for the moment4 ,what does concern us is a third hypothesis1 namely1 that if the planets really determine the periodicity of sunspots1 even though not supplying the energy1 the sun in its flight through space must have been repeatedly and more strongly influenced in the same way by many other heavenly bodies4 ,in that case1 climatic changes like those of the present1 but sometimes greatly magnified1 have presumably arisen because of the constantly changing position of the solar system in respect to other parts of the universe4 ,finally1 the fourth of our secondary hypotheses postulates that at present the date of movements of the earth's crust is often determined by the fact that storms and other meteorological conditions keep changing the load upon first one part of the earth's surface and then upon another4 ,thus stresses that have accumulated in the earth's isostatic shell during the preceding months are released4 ,in somewhat the same way epochs of extreme storminess and rapid erosion in the past may possibly have set the date for great movements of the earth's crust4 ,this hypothesis1 like the other three in our secondary or non-essential group1 is still so new that only the first steps have been taken in testing it4 ,yet it seems to deserve careful study4 ,in testing all the hypotheses here discussed1 primary and secondary alike1 the first necessity is a far greater amount of quantitative work4 ,in this book there has been a constant attempt to subject every hypothesis to the test of statistical facts of observation4 ,nevertheless1 we have been breaking so much new ground that in many cases exact facts are not yet available1 while in others they can be properly investigated only by specialists in physics1 astronomy1 or mathematics4 ,in most cases the next great step is to ascertain whether the forces here called upon are actually great enough to produce the observed results4 ,even though they act only as a means of releasing the far greater forces due to the contraction of the earth and the sun1 they need to be rigidly tested as to their ability to play even this minor role4 ,still another line of study that cries aloud for research is a fuller comparison between earthquakes on the one hand and meteorological conditions and the wandering of the poles on the other4 ,finally1 an extremely interesting and hopeful quest is the determination of the positions and movements of additional stars and other celestial bodies1 the faint and invisible as well as the bright1 in order to ascertain the probable magnitude of their influence upon the sun and thus upon the earth at various times in the past and in the future4 ,perhaps we are even now approaching some star that will some day give rise to a period of climatic stress like that of the fourteenth century1 or possibly to a glacial epoch4 ,or perhaps the variations in others of the nearer stars as well as ,alpha ,centauri may show a close relation to changes in the sun4 ,throughout this volume we have endeavored to discover new truth concerning the physical environment that has molded the evolution of all life4 ,we have seen how delicate is the balance among the forces of nature1 even though they be of the most stupendous magnitude4 ,we have seen that a disturbance of this balance in one of the heavenly bodies may lead to profound changes in another far away4 ,yet during the billion years1 more or less1 of which we have knowledge1 there appears never to have been a complete cataclysm involving the destruction of all life4 ,one star after another1 if our hypothesis is correct1 has approached the solar system closely enough to set the atmosphere of the sun in such commotion that great changes of climate have occurred upon the earth4 ,yet never has the solar system passed so close to any other body or changed in any other way sufficiently to blot out all living things4 ,the effect of climatic changes has always been to alter the environment and therefore to destroy part of the life of a given time1 but with this there has invariably gone a stimulus to other organic types4 ,new adaptations have occurred1 new lines of evolutionary progress have been initiated1 and the net result has been greater organic diversity and richness4 ,temporarily a great change of climate may seem to retard evolution1 but only for a moment as the geologist counts time4 ,then it becomes evident that the march of progress has actually been more rapid than usual4 ,thus the main periods of climatic stress are the most conspicuous milestones upon the upward path toward more varied adaptation4 ,the end of each such period of stress has found the life of the world nearer to the high mentality which reaches out to the utmost limits of space1 of time1 and of thought in the search for some explanation of the meaning of the universe4 ,each approach of the sun to other bodies1 if such be the cause of the major climatic changes1 has brought the organic world one step nearer to the solution of the greatest of all problems1--the problem of whether there is a psychic goal beyond the mental goal toward which we are moving with ever accelerating speed4 ,throughout the vast eons of geological time the adjustment of force to force1 of one body of matter to another1 and of the physical environment to the organic response has been so delicate1 and has tended so steadily toward the one main line of mental progress that there seems to be a purpose in it all4 ,if the cosmic uniformity of climate continues to prevail and if the uniformity is varied by changes as stimulating as those of the past1 the imagination can scarcely picture the wonders of the future4 ,in the course of millions or even billions of years the development of mind1 and perhaps of soul1 may excel that of today as far as the highest known type of mentality excels the primitive plasma from which all life appears to have arisen4 ,,index 99 ,indicates illustrations4 ,abbot1 ,c4 ,g41 cited1 #de1 #eb1 #bcg1 #bch1 #bci4 ,aboskun1 #ajd4 ,africa1 earthquakes1 #cja2 ,east1 see ,east ,africa2 lakes1 #adc2 ,north1 see ,north ,africa4 ,african glaciation1 #bff4 ,air1 see ,atmosphere4 ,alaska1 glacial till in1 #bhg2 ,ice ,age in1 #bba4 ,albrecht1 cited1 #cjd4 ,alexander1 march of1 #hh f4 ,allard1 ,h4 ,a41 cited1 #ahc1 #ahd4 ,alpha ,centauri1 companion of1 #bhj2 distance from sun1 #bfb2 luminosity1 #bgh2 speed of1 #bha2 variations1 #bhb4 ,alps1 loess in1 #aei2 precipitation in1 #ada2 snow level in1 #aci4 ,altair1 companion of1 #bhj2 luminosity1 #bgh2 speed of1 #bha4 ,amazon forest1 temperature1 #ag4 ,ancylus lake1 #bag4 ,andes1 snow line1 #aci4 ,animals1 climate and1 #a4 ,antarctica1 mild climate1 #bai2 thickness of ice in1 #abe2 winds1 #ace1 #afa4 ,anti-cyclonic hypothesis1 #ace ff4 ,appalachians1 effect on ice sheet1 #aba4 ,arabia1 civilization in1 #fg4 ,aral1 ,sea of1 #ajh4 ,archean rocks1 #baa4 ,archeozoic1 #c f42 climate of1 #bfg4 ,arctic ,ocean1 submergence1 #bai4 ,arctowski1 ,h41 cited1 #bi1 #df1 #bdd4 ,argon1 increase of1 #bcf4 ,arizona1 rainfall1 #hi1 #ajh2 trees measured in1 #gc4 ,arrhenius1 ,s41 cited1 #cf1 #bed4 ,arsis1 of pulsation1 #bd4 ,asbjoern ,selsbane1 corn of1 #aja4 ,asia1 atmospheric pressure1 #bih2 central1 changes of climate1 99#ge2 central1 post-glacial climate1 #bga2 climate1 #ff2 glaciation in1 #aca2 storminess in1 #fj2 western1 climate in1 #hd f4 ,atlantic ,ocean1 storminess1 #eg4 ,atmosphere1 changes1 #ai f41 #bbi2 composition of1 #bbc-bda2 effect on temperature1 #bca4 ,atmospheric circulation1 glaciation and1 #db4 ,atmospheric electricity1 solar relations of1 #ef4 ,atmospheric pressure1 earthquakes and1 #bih2 evaporation and1 #bcg2 increase in1 #bci2 redistribution of1 #di2 variation1 #ec4 ,australia1 ,east1 mild climate1 #bai2 precipitation1 #add4 ,axis1 earth's1 #dh2 wabbling of1 #cja4 ,bacon1 ,sir ,francis1 cited1 #bg4 ,bacubirito1 meteor at1 #bdf4 ,baltic ,sea1 as lake1 #bag2 freezing of1 #ajj2 ice1 #bf2 storm-floods1 #ii2 submergence1 #bai4 ,bardsson1 ,ivar1 #ajf4 ,barkow1 cited1 #ace4 ,barometric pressure1 solar relations of1 #ef4 ,barrell1 ,j41 cited1 #c1 #bjj1 #bac1 #bcd4 ,bartoli1 ,a4 ,g41 cited1 #beg4 ,bauer1 ,l4 ,a41 cited1 #aej4 ,beaches1 under water1 #ig4 ,beadnell1 ,h4 ,j4 ,l41 cited1 #adc4 ,beluchistan1 rainfall1 #hi4 ,bengal1 ,bay of1 cyclones in1 #adi4 ,bengal1 famine in1 #ajd f4 ,berlin1 rainfall and temperature1 #ic4 ,betelgeuse1 #bei f42 distance from sun1 #bfb4 ,bible1 climatic evidence in1 #ia f42 palms in1 #ib4 ,binary stars1 #beb4 ,birkeland1 ,k41 cited1 #bdd4 ,black ,earth region1 loess in1 #aei4 ,boca1 ,cal41 correlation coefficients1 #hc1 #he4 ,boltzmann1 ,l41 cited1 #beg4 ,bonneville1 ,lake1 #adb1 #adc4 ,borkum1 storm-flood in1 #ii4 ,boss1 ,l4 cited1 #bfh1 #bfi4 ,botanical evidence of mild climates1 #afg ff4 ,boulders1 on ,irish coast1 #aai4 ,bowie1 ,w41 cited1 #bic4 ,bowman1 ,i41 cited1 #bac4 ,britain1 forests1 #bbj2 level of land1 #bbj4 ,british ,isles1 height of land1 #aaa2 temperature1 #baf4 ,brooks1 ,c4 ,e4 ,p41 cited1 #aae1 #adc1 #aif1 #bae1 #bbe4 ,brooks1 ,c4 ,f41 cited1 #bji4 ,brown1 ,e4 ,w41 cited1 #aia1 #bdd4 ,brueckner1 ,e41 cited1 #bg4 ,brueckner periods1 #bg f4 ,bufo1 habitat of1 #bjb4 ,buhl stage1 #baf4 ,bull1 ,dr41 cited1 #ajj1 #aja4 ,butler1 ,h4 ,c41 cited1 #ff1 #fg ff41 #gj1 #gf4 ,california1 changes of climate1 99#ge2 correlations of rainfall1 #hf2 measurements of sequoias in1 #gc1 #gd ff42 rainfall1 #ajh4 ,cambrian period1 #d f4 ,canada1 storminess1 #ec f41 #eg2 storm tracks in1 #aac4 ,cape ,farewell1 shore ice at1 #aje4 ,carbon dioxide1 erosion and1 #aai f42 from volcanoes1 #bc2 hypothesis1 #aci2 importance of1 #i1 #aa f42 in ,permian1 #adh2 in atmosphere1 #bj1 #if1 #bch2 in ocean1 #bbf2 nebular hypothesis and1 #bcb2 theory of glaciation1 #cf ff4 ,caribbean mountains1 origin of1 #aic4 ,carnegie ,institution of ,washington1 #gd4 ,caspian ,sea1 climatic stress1 #ajd2 rainfall1 #ajg f42 rise and fall1 #bg2 ruins in1 #ga4 ,cenozoic1 climate1 #bff2 fossils1 #ba4 ,central ,america1 ,maya ruins1 #ie4 ,chad1 ,lake1 swamps of1 #aga4 ,chamberlin1 ,r4 ,t41 cited1 #aff1 #bcc1 #bfi4 ,chamberlin1 ,t4 ,c41 cited1 #ai1 #cf1 #ch1 #ci1 #db f41 #dh1 #abb1 #abe1 #aeb1 #aef1 #aij1 #aie1 #bbg1 #bfi4 ,chandler1 ,s4 ,c41 cited1 #cja4 ,chinese earthquakes1 periodicity of1 #bde4 ,chinese1 sunspot observations1 #ajh f4 ,chinese ,turkestan1 desiccation in1 #ff4 ,chronology1 glacial1 #bae4 ,clarke1 ,f4 ,w41 cited1 #bbf1 #bce4 ,clayton1 ,h4 ,h41 cited1 #agc f4 ,climate1 effect of contraction1 #ahi ff42 affect of salinity1 #bbd2 in history1 #fd-ig2 uniformity1 #a-ae2 variability1 #af-cb4 ,climates1 mild1 causes of1 #aff-ahg2 mild1 periods of1 #bgd4 ,climatic changes1 and crustal movements1 #bhe ff42 hypotheses of1 #cc-ej2 mountain-building and1 99#be2 post-glacial crustal movements and1 #bae-bbb2 terrestrial causes of1 #ahh-bad4 ,climatic sequence1 #af f4 ,climatic stages1 post-glacial1 #bgj4 ,climatic stress1 in fourteenth century1 #ih-aji4 ,climatic uniformity1 hypothesis of1 #fe1 #ga f4 ,climatic zoning1 #afi4 ,cloudiness1 glaciation and1 #aad1 #adg4 ,clouds1 as protection1 #aig4 ,colfax1 ,cal41 correlation coefficients1 #hc4 ,cologne1 flood at1 #ii4 ,compass1 variations1 #aej4 ,continental climate1 variations1 #ajc4 ,continents1 effect on climate1 #aaa f4 ,contraction1 effect on climate1 #ahi ff41 #aii1 #bjg2 effect on lands1 #bjg2 heat of sun and1 #ac f42 irregular1 #aie2 of the earth1 #ah2 of the sun1 #bdi2 stresses caused by1 #caj4 ,convection1 carbon dioxide and1 #bci4 ,corals1 in high latitudes1 #ba1 #ci1 #afg1 #agh4 ,cordeiro1 ,f4 ,j4 ,b41 cited1 #aha1 #ahc1 #ahf4 ,correlation coefficients1 earthquakes and sunspots1 #bia2 ,jerusalem rainfall and sequoia growth1 #hc ff42 rainfall and tree growth1 #gi ff4 ,cosmos1 effect of light1 #ahe4 ,cressey1 ,g4 ,b41 cited1 #hj4 ,cretaceous1 lava1 #baa2 mountain ranges1 #dd2 paleogeography1 99#bja2 submergence of ,north ,america1 #bjj4 ,croll1 ,j41 cited1 #cd ff41 #agf4 ,croll's hypothesis1 snow line1 #aci4 ,crust1 climate and movements of1 #fc1 #bhg1 #caj2 movements of1 #dc2 strains in1 #bb4 ,currents and planetary winds1 #agd4 ,cycads1 #afi4 ,cyclonic hypothesis1 #ig2 loess and1 #afc2 ,permian glaciation and1 #adh2 snow line1 #aci4 ,cyclonic storms1 in glacial epochs1 #adj f42 solar electricity and1 #bdc 7see ,storms1 ,storminess74 ,cyclonic vacillations1 #cj f42 nature of1 #eg ff4 ,daily vibrations1 #bh f4 ,danube1 frozen1 #ih4 ,darwin1 ,g4 ,h41 cited1 #aia4 ,daun stage1 #bag4 ,davis1 ,w4 ,m41 cited1 #bga4 ,davisson1 ,c41 cited1 #bid1 #bie1 #bii4 ,day1 ,c4 ,p41 cited1 #bci4 ,day1 length of1 #ah1 #aia4 ,dead ,sea1 palms near1 #ib4 ,death ,valley1 #adb4 ,de ,ballore1 ,m41 cited1 #big1 #bih4 ,deep-sea circulation1 rapidity1 #bbg2 salinity and1 #agf2 solar activity and1 #agi4 ,de ,geer1 ,s41 cited1 #bae1 #bba4 ,de ,lapparent1 ,a41 cited1 #bjj4 ,denmark1 fossils1 #bga4 ,desert pavements1 #afa4 ,deserts1 abundant flora of1 #aga2 and pulsations theory1 #hh ff42 red beds of1 #agj4 ,devonian1 climate1 #bff2 mountains1 #bji4 ,dog1 climate and1 #a4 ,donegal ,county1 ,ireland1 #bbj4 ,double stars1 #bgb1 #bhj2 electrical effect of1 #bfa4 ,douglass1 ,a4 ,e41 cited1 #bh1 #gc1 #gd f41 #hd1 #he1 #ajg4 ,dragon ,town1 destruction of1 #ajd1 #ajh4 ,drake1 ,n4 ,f41 cited1 #big1 #bih4 ,droughts1 and pulsations theory1 #hg f42 in ,england1 #ajb2 in ,india1 #ajd f4 ,drumkelin ,bog1 ,ireland1 log cabin in1 #bbj4 ,dust1 at high levels1 #bdj4 ,earth1 crust of and the sun1 #bhe-cag2 internal heat1 #bab2 nature of mild climate1 #bgd2 position of axis1 #aha2 rigidity of1 #cjg2 temperature gradient1 #bac2 temperature of surface1 #h4 ,earthquakes1 and seasons1 #bid1 #big2 and sunspots1 #bhh f42 and tropical hurricanes1 #cjj2 and wandering of pole1 #cjd f42 cause of1 #cjg2 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