99 99 99 99 99 ,transcriber's ,note3 ,the original publication has been replicated faithfully except as shown in the ,,transcriber',s ,,amendments near the end of the text4 ,to preserve the alignment of tables and headers1 this etext presumes a mono-spaced font on the user's device1 such as ,courier ,new1 but another choice such as the proportional ,lucida ,sans ,unicode font might render odd characters better4 ,words in italics are indicated like this4 ,text emphasized with bold characters or other treatment is shown like this4 99 99 99 99 99 ,,practical ,,exercises ,,in ,,elementary ,,meteorology ,,by ,,robert ,,decourcy ,,ward ,,instructor ,,in ,,climatology ,,in ,,harvard ,,university ,,boston1 ,u4,s4,a4 ,,ginn ,,company1 ,,publishers ,the ,athenum ,press #ahii ,,copyright1 #ahii1 ,,by ,,robert ,,decourcy ,,ward ,,all ,,rights ,,reserved ,,preface4 ,the advance of meteorology as a school study has been much hampered by the lack of a published outline of work in this subject which may be undertaken during the school years4 ,there are several excellent text-books for more advanced study1 but there is no laboratory manual for use in the elementary portions of the science4 ,in many secondary schools some instruction in meteorology is given1 and the keeping of meteorological records by the scholars is every year becoming more general4 ,there is yet1 however1 but little system in this work1 and1 in consequence1 there is little definite result4 ,the object of this book is to supply a guide in the elementary observational and inductive studies in meteorology4 ,this ,manual is not intended to replace the text-books1 but is designed to prepare the way for their more intelligent use4 ,simple preliminary exercises in the taking of meteorological observations1 and in the study of the daily weather maps1 as herein suggested1 will lay a good foundation on which later studies1 in connection with the text-books1 may be built up4 ,explanations of the various facts discovered through these exercises are not considered to lie within the scope of this book4 ,they may be found in any of the newer text-books4 ,this ,manual lays little claim to originality4 ,its essential features are based on the recommendations in the ,report on ,geography of the ,committee of ,ten4 ,a scheme of laboratory exercises1 substantially the same as that proposed in this ,report1 was1 for some fifteen years1 the basis of the work in elementary meteorology done in ,harvard ,college under the direction of ,professor ,william ,m4 ,davis4 ,the plan proposed by the ,committee of ,ten has been thoroughly tested by the writer during the past five years1 not only in college classes1 but also in ,university ,extension work among school teachers1 and the present book embodies such modifications of that scheme and additions to it as have been suggested by experience4 ,emphasis is laid throughout this ,manual on the larger lessons to be learned from the individual exercises1 and on the relations of various atmospheric phenomena to human life and activities4 ,no attempt is made to specify in exactly what school years this work should be undertaken4 ,at present1 and until meteorology attains a recognized position as a school study1 teachers must obviously be left to decide this matter according to the opportunities offered in each school4 ,the general outline of the work1 however1 as herein set forth1 is intended to cover the grammar and the high school years1 and may readily be adapted by the teacher to fit the circumstances of any particular case4 ,this book contains specific instructions to the student as to the use of the instruments2 the carrying out of meteorological observations2 the investigation of special simple problems by means of the instruments2 and the practical use of the daily weather maps4 ,the ,notes for the ,teacher1 at the end of the book1 are explanatory1 and contain suggestions which may be useful in directing the laboratory work of the class4 ,it has been the privilege of the author during the past ten years to study the science of meteorology1 and the methods of teaching that science1 under the constant direction of ,professor ,william ,morris ,davis1 of ,harvard ,university4 ,to ,professor ,davis the author is further indebted for many valuable suggestions in connection with the arrangement and treatment of the subject-matter of this book4 ,thanks are due also to ,mr4 ,william ,h4 ,snyder1 of ,worcester 7,mass47 ,academy1 and to ,mr4 ,john ,w4 ,smith1 ,local ,forecast ,official of the ,united ,states ,weather ,bureau1 ,boston1 ,mass41 for valued criticisms4 ,,robert ,,dec4 ,,ward4 ,,harvard ,,university1 ,,cambridge1 ,,mass41 ,september1 #ahii4 ,,contents4 ,,introduction4 ,,page ,,the ,,importance ,,of ,,meteorology3 ,,its ,,relations ,,to ,,man xi ,,part ,i4----,,non-,,instrumental ,,observations4 ,,chapter ,i4----,,observations ,,of ,,temperature1 ,,wind ,,direction ,,and ,,velocity1 ,,state ,,of ,,sky1 ,,and ,,rainfall #a ,,part ,,ii4----,,instrumental ,,observations4 ,,chapter ,,ii4----,,elementary ,,instrumental ,,observations #aa ,,chapter ,,iii4----,,advanced ,,instrumental ,,observations #bf ,,part ,,iii4----,,exercises ,,in ,,the ,,construction ,,of ,,weather ,,maps4 ,,chapter ,,iv4----,,the ,,daily ,,weather ,,map #dg ,,chapter ,v4----,,temperature #ea ,,chapter ,,vi4----,,winds #gj ,,chapter ,,vii4----,,pressure #gf ,,chapter ,,viii4----,,weather #he ,,part ,,iv4----,,the ,,correlations ,,of ,,the ,,weather ,,elements ,,and ,,weather ,,forecasting4 ,,chapter ,,ix4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,pressure #ia ,,chapter ,x4----,,correlation ,,of ,,the ,,velocity ,,of ,,the ,,wind ,,and ,,the ,,pressure #ic ,,chapter ,,xi4----,,form ,,and ,,dimensions ,,of ,,cyclones ,,and ,,anticyclones #if ,,chapter ,,xii4----,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,and ,,their ,,wind ,,circulation #ih ,,chapter ,,xiii4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,temperature #aja ,,chapter ,,xiv4----,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,and ,,their ,,temperatures #ajd ,,chapter ,,xv4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,weather #ajf ,,chapter ,,xvi4----,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,and ,,the ,,weather #aji ,,chapter ,,xvii4----,,progression ,,of ,,cyclones ,,and ,,anticyclones #aaa ,,chapter ,,xviii4----,,sequence ,,of ,,local ,,weather ,,changes #aac ,,chapter ,,xix4----,,weather ,,forecasting #aad ,,part ,v4----,,problems ,,in ,,observational ,,meteorology4 ,,chapter ,,xx4----,,temperature #abe ,,chapter ,,xxi4----,,winds #acj ,,chapter ,,xxii4----,,humidity1 ,,dew1 ,,and ,,frost #acb ,,chapter ,,xxiii4----,,clouds ,,and ,,upper ,,air ,,currents #acf ,,chapter ,,xxiv4----,,precipitation #ach ,,chapter ,,xxv4----,,pressure #aci ,,chapter ,,xxvi4----,,meteorological ,,tables #adb ,,appendix ,a4 ,,suggestions ,,to ,,teachers #aga ,,appendix ,b4 ,,the ,,equipment ,,of ,a ,,meteorological ,,laboratory #ahf ,,index #aig ,,acknowledgment ,,of ,,figures4 #a1 #g1 #h1 #i1 #aj1 #af4 ,meteorological ,instruments4 ,h4 ,j4 ,green1 #aaia ,bedford ,avenue1 ,brooklyn1 ,n4 ,y4 #b1 #d4 ,instrument ,shelter and ,rain ,gauge4 ,instructions for ,voluntary ,observers4 ,united ,states ,weather ,bureau4 #e4 ,mercurial ,barometer4 ,l4 ,e4 ,knott ,apparatus ,co41 #ad ,ashburton ,place1 ,boston1 ,mass4 #ab1 #ae1 #ec4 ,thermograph and ,barograph ,curves1 and ,cyclonic ,composite4 ,davis1 ,elementary ,meteorology4 #ag4 ,nephoscope4 ,annals ,harvard ,college ,observatory1 ,vol4 ,,xx1 ,part ,i4 #dh4 ,north ,atlantic ,cyclone4 ,pilot ,chart of the ,north ,atlantic ,ocean4 ,united ,states ,hydrographic ,office4 #ea4 ,wind ,rose4 ,quarterly ,journal ,royal ,meteorological ,society1 ,vol4 ,,xxiv1 ,no4 #ajh4 ,,introduction4 ,,the ,,importance ,,of ,,meteorology3 ,,its ,,relations ,,to ,,man4 ,we live in the laboratory of the earth's atmosphere4 ,the changes from hot to cold1 wet to dry1 clear to cloudy1 or the reverse1 profoundly affect us4 ,we make and unmake our daily plans2 we study or we enjoy vacations2 we vary our amusements and our clothing according to these changes4 ,the weather forecasts for the day in the newspaper are read even before the telegraphic despatches of important events4 ,sailors about to put to sea govern themselves according to the storm warnings of our ,weather ,bureau4 ,farmers and shippers of fruit1 meat1 and vegetables anxiously watch the bulletins of cold or warm waves1 and guard against damage by frost or excessive heat4 ,steam and electric railways prepare their snow-plows when a severe snowstorm is predicted4 ,meteorology1 the science of the atmosphere1 is thus of very great interest and importance4 ,there is no subject a knowledge of which does more to make our daily life interesting4 ,since we live in the midst of the atmosphere and cannot escape from the changes that take place in it1 we must1 consciously or unconsciously1 become observers of these changes4 ,examples of the varying processes at work in the atmosphere are always with us4 ,there is no end to the number and the variety of our illustrations of these processes4 ,man is so profoundly affected by weather changes from day to day that all civilized countries have established weather services4 ,observers taking regular weather records are stationed at thousands of different places in all parts of the world1 and the observations which they make are used by meteorologists in preparing daily weather maps and forecasts1 and in studying the conditions of temperature1 winds1 and rainfall4 ,in the ,united ,states alone there are about #cjjj of these observers4 ,these observations are not made on land only4 ,hundreds of ship captains on all the oceans of the world are making their regular daily meteorological records1 which at the end of the voyage are sent to some central office1#a where they are studied and employed in the preparation of ,pilot ,charts for the use of mariners4 ,by means of these ocean meteorological observations1 which were first systematized and carried out on a large scale under the direction of ,lieutenant ,matthew ,fontaine ,maury 7born1 #ahjf2 died1 #ahgc71 of the ,united ,states ,navy1 it has become possible to lay out the most favorable sailing routes for vessels engaged in commerce in all parts of the world4 ,footnote #a3 ,in the ,united ,states1 marine meteorological observations are forwarded to the ,united ,states ,hydrographic ,office1 ,navy ,department1 ,washington4 ,so important is a knowledge of the conditions of the winds and the weather1 that scientific expeditions into unexplored or little-known regions give much of their time to meteorological observations4 ,on the famous ,lady ,franklin ,bay ,expedition 7#ahha-ahhd7 of ,lieutenant 7now ,general7 ,a4 ,w4 ,greely1 of the ,united ,states ,army1 meteorological observations were kept up by the few feeble survivors1 after death by disease and starvation had almost wiped out the party altogether1 and when those who were left had but a few hours to live unless rescue came at once4 ,on ,nansen's expedition to the 8,farthest ,north10 on ,peary's trips to ,greenland1 and on every recent voyage to the ,arctic or the ,antarctic1 meteorological instruments have formed an important part of the equipment4 ,not content with obtaining records from the air near the earth's surface1 meteorologists have sent up their instruments by means of small1 un-manned balloons to heights of #aj miles2 and the use of kites for carrying up such instruments has been so successful that1 at ,blue ,hill ,observatory1 near ,boston1 ,mass41 records have been obtained from a height of over #b miles4 ,observatories have also been established on mountain summits1 where meteorological observations have been made with more or less regularity4 ,such observatories are those on ,pike's ,peak1 ,colorado 7#ad1acd feet71 ,mont ,blanc1 ,switzerland 7#ae1ghj feet71 and on ,el ,misti1 in southern ,peru4 ,the latter1 #ai1bjj feet above sea level1 is the highest meteorological station in the world4 ,the study of the meteorological conditions prevailing over the earth has thus become of world-wide importance4 ,in the following exercises we shall carry out1 in a small way1 investigations similar to those which have occupied and are now occupying the attention of meteorologists all over the world4 ,,practical ,,exercises ,,in ,,elementary ,,meteorology4 ,,part ,i4----,,non-,,instrumental ,,observations4 ,,chapter ,i4 ,,observations ,,of ,,temperature2 ,,wind ,,direction ,,and ,,velocity2 ,,state ,,of ,,sky1 ,,and ,,rainfall4 ,before beginning observations with the ordinary instruments1 accustom yourself to making and recording observations of a general character1 such as may be carried out without the use of any instruments whatever4 ,such records include3 ,temperature2 ,wind ,direction and ,velocity2 ,state of the ,sky1 and ,rainfall4 ,temperature4----,in keeping a record#b of temperature without the use of a thermometer1 excellent practice is given in observations of the temperature actually felt by the human body4 ,our bodies are not thermometers4 ,they do not indicate1 by our sensations of heat or cold1 just what is the temperature of the surrounding air1 but they try to adjust themselves to the conditions in which they are4 ,this adjustment depends on many things beside the temperature of the air2 e4g41 the moisture or humidity of the air2 the movement of the air2 the temperature and the nearness of surrounding objects4 ,in summer1 a day on which the temperature reaches #hj or #he often seems much hotter than another day on which the temperature rises to #ie4 ,in winter1 temperatures registered by the thermometer as #aj or #ae above zero often feel a great deal colder than temperatures of -#e or -#aj4 ,in recording your observations on temperature1 the record book may be divided into columns as follows3---- ,footnote #b3 ,each scholar will need a blank book in which to preserve the observations4 ,,sample ,,record ,,of ,,temperature4 ---------------------------------------- ---------------------------- ,,date4 ,,hour4 ,,temperature4 ,,remarks4 ---------------------------------------- --------------------------- ,jan4 #af #i ,a4,m4 ,chilly 8 8 #ab ,m4 ,warmer 8 8 #d ,p4,m4 8 ,growing slowly warmer all day4 8 #ag #h ,a4,m4 ,warm ,about the same as ,jan4 #af1 #d ,p4,m4 8 8 #aa ,a4,m4 ,cooler ,began to grow cooler about #aj ,a4,m4 8 8 #c ,p4,m4 ,colder ,steadily becoming colder4 ---------------------------------------- ---------------------------- ,the following are some of the questions you should ask yourself in carrying out this work4 ,it is not expected that you will be able to answer all these questions at once1 but that you will keep them in mind during your studies1 and try to discover the answers1 as a result of your own observations4 ,how does it feel to you out of doors to-day8 ,is it hot1 warm1 cool1 or cold8 ,what is the difference between your feelings yesterday and to-day8 ,between day before yesterday and to-day8 ,have you noticed any regular change in your feelings as to warmth and cold during three or four successive days8 ,during the past week or two8 ,during the past month8 ,is there any difference between the temperature of morning1 noon1 afternoon1 and evening8 ,is there any regular variation in temperature during the day8 ,have there been any sudden changes in temperature during the last few days8 ,have these sudden changes brought warmer or cooler weather8 ,has the warmer or cooler weather continued for a day or so1 or has another change quickly followed the first8 ,have the sudden changes1 if you have noted any1 come at any regular times 7as morning1 afternoon1 evening7 or at irregular intervals8 ,does there seem to you to be any definite system1 of any kind1 in our changes of temperature8 ,in what ways are people in general affected by hot weather8 ,by cold weather8 ,what difference does a very hot or a very cold day make in your own case8 ,wind ,direction and ,velocity4----,wind is an important meteorological element because it has many close relations to human life4 ,it affects very markedly our bodily sensations of heat or cold4 ,a cold1 calm day is pleasanter than a cold1 windy day4 ,on the other hand1 a hot1 calm day is usually much more uncomfortable than a hot1 windy day4 ,high winds cause wrecks along seacoasts and damage houses1 crops1 and fruit trees4 ,sea breezes bring in fresh1 cool1 pure air from the ocean on hot summer days4 ,in the tropics the sea breeze is so important in preserving the health of ,europeans in many places that it is known as 8the doctor40 ,the movement of wind through large cities carries off the foul air which has collected in the narrow streets and alleys1 and is thus a great purifying agent4 ,record the direction of the wind according to the four cardinal points of the compass 7,n41 ,e41 ,s41 and ,w47 and the four intermediate points 7,,ne41 ,,se41 ,,sw41 and ,,nw474 ,the direction of the wind is the point from which the wind blows4 ,you can determine the points of the compass roughly by noting where the sun rises and where it sets4 ,note the velocity of the wind according to the following scale1 proposed by ,professor ,h4 ,a4 ,hazen of the ,united ,states ,weather ,bureau4 #j ,,calm4 #a ,,light2 just moving the leaves of trees4 #b ,,moderate2 moving branches4 #c ,,brisk2 swaying branches2 blowing up dust4 #d ,,high2 blowing up twigs from the ground1 swaying whole trees4 #e ,,gale2 breaking small branches1 loosening bricks on chimneys4 #f ,,hurricane or ,,tornado2 destroying everything in its path4 ,the record book will need two additional columns when wind observations are begun1 as follows3---- ,,sample ,,record ,,of ,,temperature ,,and ,,wind4 ---------------------------------------- ---------------------------------------- - ,,wind ,,wind ,,date4 ,,hour4 ,,temperature4 ,,direction4 ,,velocity4 ,,remarks4 ---------------------------------------- ---------------------------------------- - ,oct4 #c #g4cj ,a4,m4 ,cool ,,ne4 ,moderate ,temperature falling since last evening4 ,wind velocity increasing4 8 8 #aa ,a4,m4 8 8 8 8 ,brisk ,temperature the same4 ,wind velocity still increasing4 8 8 #c ,p4,m4 8 8 8 8 ,high ,wind velocity still increasing4 ---------------------------------------- ---------------------------------------- - ,what is the direction of the wind to-day8 ,what is its velocity8 ,has its direction or velocity changed since yesterday8 ,if so1 was the change sudden or gradual8 ,have you noticed any calms8 ,what was the direction of the wind before the calm8 ,what after the calm8 ,does there seem to be more wind from one compass point than from another8 ,is there any relation between the direction of the wind and its velocity8 i4e41 is the ,,nw4 wind1 for instance1 usually a brisk or a high wind1 or1 is the ,,se4 or ,s4 wind usually moderate8 ,does the wind usually change its direction gradually1 as from ,,se4 to ,s41 then to ,,sw41 then to ,w41 etc41 or does it jump all at once1 as from ,,se4 to ,w48 ,is there any relation between the velocity of the wind and the hour of the day1 i4e41 does the wind seem stronger or weaker at noon than in the morning or at night8 ,is it a common occurrence to have a wind from the same direction for several successive days1 or are we apt to have different winds almost every day8 ,do you notice any systematic changes in wind direction which are often repeated8 ,what are these changes8 ,can you make a simple rule for them8 ,in what ways does the wind affect us8 ,state of the ,sky4----,by the state of the sky is meant the condition of the sky as to its cloudiness4 ,clouds add much to the beauty and variety of nature4 ,they are often gorgeously colored at sunset4 ,by their changes in form1 color1 and amount from day to day they relieve what might otherwise be a wearisome succession of the same weather types4 ,prevailingly overcast skies have a depressing effect4 ,prevailingly clear skies become monotonous4 ,a proper amount of bright sunshine is essential for the ripening of crops1 but too much sunshine may parch soil and vegetation1 and become injurious4 ,clouds bring rain2 hence a sufficient amount of cloudiness is just as necessary as a sufficient amount of sunshine4 ,the drift of clouds shows us the direction of movement of the air above us1 and is of considerable help in forecasting the weather4 ,fog1 which is a very low cloud1 is in some cases so common as to be a meteorological element of great importance4 ,in the city of ,london1 where fogs are very prevalent1 especially in winter1 the average number of hours of bright sunshine in ,december and ,january is only fifteen in each month4 ,the ,london fogs are1 in great part1 due to the presence in the air of vast numbers of particles of soot and smoke from millions of fires4 ,these particles increase the density of the fog and prolong its duration4 ,the amount of cloudiness is recorded on a scale of tenths4 ,a clear sky is one that is less than #c_/aj cloudy2 a fair sky is from #c_/aj to #g_/aj cloudy2 and a cloudy sky is over #g_/aj cloudy4 ,in observing the state of the sky1 note such points as the times of clouding and of clearing2 the arrangement of the clouds1 i4e41 whether they are few and scattered1 or cover the sky with a uniform layer2 the common forms of clouds2 the changes in the amounts of cloudiness1 etc4 ,another new column must be added in the record book for the cloudiness4 ,the table will now appear thus3---- ,,sample ,,record ,,of ,,temperature1 ,,wind1 ,,and ,,state ,,of ,,the ,,sky4 ---------------------------------------- ---------------------------------------- ---- ,,wind4 ,,state ,,date4 ,,hour4 ,,temperature4 --------------------- ,,of ,,sky4 ,,remarks4 ,,direction4 ,,velocity4 ---------------------------------------- ---------------------------------------- --- ,dec4 #ah #i ,a4,m4 ,very cold ,,nw4 ,brisk ,clear ,very cold all night4 ,everything frozen up4 8 8 #e ,p4,m4 8 8 8 8 8 ,same conditions4 8 #ai #h4cj ,a4,m4 ,a little 8 ,moderate ,fair ,wind less violent4 warmer ,small clouds scattered over the sky4 ---------------------------------------- ---------------------------------------- --- ,is the sky clear1 fair1 or cloudy to-day8 ,is there more or less cloud than there was yesterday8 ,than the day before yesterday8 ,is to-day a day of increasing or of decreasing cloudiness8 ,is the sky usually perfectly clear1 or is it oftenest somewhat clouded over8 ,how long does it take for the sky to become completely covered with clouds from the time when it first begins to become cloudy8 ,when there are a few clouds in the sky1 are these usually scattered all over the sky1 or are they in groups8 ,have you noticed any particular form of clouds which seemed familiar to you8 ,do clouds seem to have certain definite shapes and appearances which are to be seen often8 ,do you discover any variation of cloudiness during the day1 i4e41 is it apt to be more cloudy in the afternoon than in the morning or at night8 ,can you make a list describing some of the clouds that you see most often8 ,can you give these common kinds of clouds some names of your own that shall describe them briefly8 ,in what ways does a clear sky1 with bright sunshine1 affect us8 ,rainfall4----,under the general term rainfall1 meteorologists include1 besides rain itself1 snow1 hail1 sleet1 etc4 ,the term precipitation is also often used4 ,rainfall stands in close relation to human life and occupations4 ,it feeds lakes and rivers1 thus furnishing means of transportation1 power for running mills and factories1 and water supplies for cities4 ,regions of abundant rainfall are usually heavily forested1 like the ,amazon valley in ,south ,america1 and parts of ,equatorial ,africa4 ,in civilized countries lumbering is apt to be an important occupation in districts of heavy rainfall1 as in ,oregon and ,washington in our own country1 and in ,southern ,chile in ,south ,america4 ,where there is a moderate rainfall1 and other conditions are favorable1 there agriculture is possible1 and farming becomes one of the chief occupations1 as in the ,mississippi and ,missouri valleys in the ,united ,states1 and in ,western ,canada4 ,districts which have a rainfall too small for successful agriculture1 but are not by any means deserts1 are often excellent grazing lands1 as in the case of parts of ,texas1 ,nebraska1 and ,kansas in the ,united ,states1 and the ,argentine ,republic in ,south ,america4 ,where there is very little rainfall deserts are found4 ,cities are not built in deserts1 because there are no occupations to attract large numbers of men4 ,the inhabitants of the desert are wandering tribes1 which move from place to place in search of water and food for themselves and their animals4 ,rain and snow cleanse the air1 washing out impurities such as dust and smoke4 ,hence they are important agents in preserving health4 ,note the kind of precipitation 7rain1 snow1 hail1 sleet72 the amount 7heavy1 moderate1 light1 trace72 and the time of the beginning and ending of the storm or shower4 ,the record book must now be further subdivided into columns1 to make room for the rainfall observations1 in this manner3---- ,,sample ,,record ,,of ,,temperature1 ,,wind1 ,,state ,,of ,,sky1 ,,and ,,precipitation4 ---------------------------------------- ---------------------------------------- ------------- ,,wind4 ,,precipitation4 ------------------- ,,state ----------------- ,,date4 ,,hour4 ,,temperature4 ,,of ,,time ,,remarks4 ,,direction4,,velocity4 ,,sky4 ,,of ,,kind4,,am',t4 ,,beginn4 ---------------------------------------- ---------------------------------------- ---------- ,mar4 #bah4cj ,a4,m4 ,mild ,s4 ,light ,overcast#h ,a4,m4 ,rain ,light ,raining4 8 8 #ab ,m4 8 8 8 ,overcast 8 8 8 8 8 #d ,p4,m4 8 8 ,moderate ,overcast ,stopped raining about #c ,p4,m4 8 #bb #h ,a4,m4 ,cool ,,nw4 ,brisk ,clear ,cleared off during the night4 ---------------------------------------- ---------------------------------------- ---------- ,does most of our rain come in brief showers1 or in storms lasting a day or two8 ,do we have about the same amount of rain or snow every week and every month1 or does the amount vary a good deal from week to week and from month to month8 ,do you notice much difference in the characteristics of successive storms1 or do they all seem pretty much alike8 ,are thunderstorms limited to any particular season of the year8 ,if so1 to what season8 ,have you discovered any rule as to the time of day when rainstorms or snowstorms begin8 ,when thunderstorms begin and end8 ,is it common or uncommon for us to have a storm lasting three or four days8 ,how long does a thunderstorm usually last8 ,do we have most hail in winter or in summer8 ,in what ways does a rainy day affect people8 ,how are you yourself affected8 ,how does a heavy snowstorm affect travel and transportation8 ,in what ways does a snowstorm differ from a rainstorm as to the character of the precipitation and its effects8 ,after studying the temperature1 wind1 state of sky1 and rainfall separately1 take two elements together and see what relation one has to the other4 ,try to answer such questions as these3---- ,temperature and ,wind4----,what relations can you discover between the direction of the wind and the temperature8 ,which winds are the coolest8 ,which the warmest8 ,does a hot1 calm day seem warmer or cooler than a hot1 windy day8 ,does a cold1 calm day seem colder or warmer than a cold1 windy day8 ,does the velocity of the wind have any effect on your feeling of cold or of warmth8 ,if so1 what effect8 ,wind and ,state of ,sky4----,has the direction of the wind anything to do with the cloudiness8 ,is there more apt to be considerable cloudiness with wind from one direction than from another8 ,what winds are usually accompanied by the largest amount of cloud8 ,what winds usually blow when the sky is clear8 ,is the relation of cloudiness to certain wind directions so close that1 if you know the wind direction1 you can make a prediction as to the probable cloudiness8 ,are the winds with clouds more common in one month than another8 ,in one season than another8 ,if so1 which month8 which season8 ,temperature and ,state of ,sky4----,do you notice any relation between the temperature and the state of the sky8 ,in winter are our coldest days usually cloudy or clear8 ,in summer are our hottest days cloudy or clear8 ,are the winds that give us the most cloudiness warm or cold winds in winter and in summer8 ,is a cloudy night colder or warmer than a clear night8 ,is a cloudy day colder or warmer than a clear day8 ,state of ,sky and ,precipitation4----,how is rainfall or snowfall related to the cloudiness8 ,do we ever have rain or snow when the sky is not completely covered with clouds8 ,does the sky usually become quickly covered with clouds before a rain8 ,does a sky wholly covered with clouds always give us rain or snow8 ,does the sky clear rapidly or slowly after a rain8 ,are any particular kinds of clouds associated with rain or with snowstorms8 ,with brief showers8 ,with thunderstorms8 ,wind and ,precipitation4----,are any particular wind directions more likely than others to give us rain or snow8 ,are these the same winds as those which give us the most cloudiness8 ,what winds are they8 ,has the velocity of the wind any relation to the rain or snowstorm8 ,does the wind blow harder before1 during1 or after the rain or snow8 ,what changes of wind direction have you noted before1 during1 and after any storm8 ,have you noticed these same changes in other storms8 ,are they so common in our storms that you can make a rule as to these changes8 ,temperature and ,precipitation4----,does a shower or a rainstorm in the hotter months affect the temperature of the air in any way8 ,how8 ,in the winter does the temperature show any changes before a snowstorm8 ,is it usually warmer or colder then than a day or two before the storm and the day after8 ,is it usually uncomfortably cold during a snowstorm8 ,are rainy spells in the spring and the autumn months cooler or warmer than clear dry weather8 ,,part ,,ii4----,,instrumental ,,observations4 ,,chapter ,,ii4 ,,elementary ,,instrumental ,,observations4 ,the non-instrumental observations1 suggested in the preceding chapter1 prepare the way for the more exact records of the weather elements which are obtainable only by the use of instruments4 ,the non-instrumental records are not to be entirely given up1 even after the instrumental work and the weather-map exercises have begun1 but should be continued throughout the course4 ,notes on the forms and changes of clouds1 on the times of beginning and ending1 and on the character of the precipitation1 as outlined in the last chapter1 and other observations made without the use of instruments1 are an essential part of even the most advanced meteorological records4 ,the simpler instruments are the ordinary thermometer1 the wind vane1 the rain gauge1 and the mercurial barometer 7in a modified form74 ,observations with these instruments1 although of a simple character1 can be made very useful4 ,the advance over the non-instrumental observations1 which latter may be termed observations of sensation1 is a decided one4 ,in place of the vague and untrustworthy statements concerning hot and cold1 warm and cool days1 we now have actual degrees of temperature to serve as a basis for comparison of day with day or month with month4 ,the measurements of rain and snowfall enable us to study the amounts brought in different storms1 the average precipitation of the various months1 etc4 ,the important facts of change of pressure now become known1 and also the relation of these changes to the weather4 ,just as we have1 in the earlier work1 become familiar with our typical weather changes and types1 so we shall now have our eyes opened to the actual values of the temperatures and precipitation connected with these changes4 ,illustration3 ,,fig4 #a4 ,the ordinary thermometer 7,greek3 heat measure71 the most commonly used and most widely known of all meteorological instruments1 was in an elementary form known to ,galileo1 and was used by him in his lectures at the ,university of ,padua during the years #aeib to #afji4 ,thermometers enable us to measure the temperatures of different bodies by comparison with certain universally accepted standards of temperature4 ,these standards are the freezing and boiling points of distilled water4 ,in its common form the thermometer consists of a glass tube1 closed at the top1 and expanding at its lower end into a hollow spherical or cylindrical glass bulb4 ,this bulb and part of the tube are filled with mercury or alcohol4 ,as the temperature rises1 the liquid expands1 flows out of the bulb1 and rises in the tube4 ,as the temperature falls1 the mercury or alcohol contracts1 and therefore stands at a lower level in the tube4 ,in order that the amount of this rise or fall may be accurately known1 some definite scale for measurement must be adopted4 ,the scale commonly used in this country owes its name to ,fahrenheit 7born in ,danzig in #afhf2 died in #agcf71 who was the first to settle upon the use of mercury as the liquid in thermometers1 and also the first definitely to adopt two fixed points in graduating the scale4 ,the division of this scale into #ahj between the freezing point 7#cb7 and the boiling point 7#bab7 seems to have been taken from the graduation of a semicircle4 ,fahrenheit was a manufacturer of all sorts of physical apparatus1 and it has been thought probable that he had some special facilities for dividing his thermometer tubes into #ahj parts4 ,mercury is most commonly used as the liquid in thermometers1 because it readily indicates changes of temperature1 and because over most of the world the winter cold is not sufficient to freeze it4 ,the freezing point of mercury is about #dj below zero 7-#dj ,f474 ,alcohol1 which has a much lower freezing point1 is therefore used in thermometers which are to be employed in very cold regions4 ,alcohol thermometers must1 for instance1 be used in ,northern ,siberia1 where the mean ,january temperature is #fj below zero4 ,the temperature which meteorologists desire to obtain by the ordinary thermometer is the temperature of the free air in the shade4 ,in order that thermometers may indicate this temperature1 they must1 if possible1 be placed in an open space where there is an unobstructed circulation of the air1 and they must be protected from the direct rays of the sun4 ,they are1 therefore1 usually exposed inside of a cubical enclosure of wooden lattice work1 in an open space away from buildings1 and at a height of #d to #aj feet above the ground1 preferably a grass-covered surface4 ,this enclosure is called the shelter1 and its object is to screen the instrument from the direct and reflected sunshine1 to allow free circulation of air around the bulb1 and to keep the thermometer dry4 ,sometimes the shelter1 instead of being in an open space on the ground1 is built on the roof or against the north wall of a building1 or outside of one of the windows4 ,fig4 #b shows an ordinary shelter4 ,a still simpler method of exposure is described in the 8,instructions for ,voluntary ,observers0 7,united ,states ,weather ,bureau1 #ahib7 as follows3 8,select a north window1 preferably of an unoccupied room1 especially in winter4 ,fasten the blinds open at right angles to the wall of the house4 ,fasten a narrow strip #c inches wide across the window outside1 and from #h to #ab inches from the window-pane4 ,to this fasten the thermometers40 ,if none of these methods of sheltering the instrument is feasible1 the thermometer may be fastened to the window frame1 about a foot from the window1 and so arranged that it can be read from the inside of the room without opening the window4 ,illustration3 ,,fig4 #b4 ,readings of the thermometer1 to the nearest degree of temperature indicated on the scale by the top of the mercury column1 are to be made at the regular observation hours1 and are to be entered in your record book4 ,temperatures below zero are preceded by a minus sign 7-74 ,a table similar to that suggested towards the close of the last chapter 7p4 #h7 may be used in keeping these instrumental records1 except that actual thermometer readings can now be entered in the column headed 8,temperature10 instead of using only the general terms warm1 cold1 chilly1 etc4 ,this is a great gain4 ,you will now be able to give fairly definite answers to many of the questions asked in ,chapter ,i4 ,answer these questions with the help of your thermometer readings1 as fully as you can4 ,the greater part of the ,temperate ,zone1 in which we live1 is peculiar in having frequent and rapid changes of temperature1 not only from season to season1 but from day to day1 and during a single day4 ,in winter1 we are apt to have a warm wind immediately after a spell of crisp cold weather4 ,in summer1 cloudy1 cool days come as a sudden relief when we have been suffering from intense heat1 with brilliant sunshine4 ,these changes give a variety to our climate which is1 on the whole1 very beneficial to man4 ,the ,north ,temperate ,zone1 with strong seasonal changes in temperature and weather1 is the zone of the highest civilization and of the greatest energy of man4 ,in the ,torrid ,zone the changes of temperature are1 as a whole1 small4 ,there is no harsh winter4 ,the climate is monotonous and deadening1 rather than enlivening4 ,man finds it easy to live without much work1 and the inhabitants of the ,torrid ,zone have not1 as a rule1 advanced far in the scale of civilization4 ,the wind vane used by the ,weather ,bureau is about #f feet long1 and has a divided tail made of pine boards1 the two pieces making an angle of #bb-a_/b4 ,the purpose of this divided tail is to steady the vane and to make it more sensitive to light currents4 ,illustration3 ,,fig4 #c4 ,a common wind vane on a neighboring church steeple or flagstaff will usually serve sufficiently well for ordinary use4 ,observations of wind direction 7to eight compass points7 are to be made as a part of the ordinary weather record1 and to be entered in the proper column of the record book4 ,the rain gauge consists of three separate parts1 the receiver ,a1 the overflow attachment ,b1 and the measuring tube ,c4 ,illustration3 ,,fig4 #d4 ,the inside diameter of the top of the receiver in the standard ,weather ,bureau gauge is #h inches 7at a in ,fig4 #d74 ,this receiver has a funnel-shaped bottom1 so that all the precipitation which falls into it is carried at once into the measuring tube ,c1 whose inside height is #bj inches4 ,the diameter of the measuring tube is #b4ec inches4 ,the rain falling into the receiver ,a fills this tube ,c to a depth greater than the actual rainfall1 in proportion as the area of the receiver is greater than the area of the measuring tube4 ,in the standard ,weather ,bureau gauges the ratio of the area of the receiver to the area of the measuring tube is such that the depth of rainfall is magnified exactly ten times4 ,the object of magnifying the amount in this way is to measure a very small quantity more easily4 ,the narrow portion of the receiver d fits over the top of the measuring tube1 holding the latter firmly in place and preventing any loss of rainfall4 ,an opening1 e1 in the lower portion of the receiver d1 just on a level with the top of the measuring tube1 serves as an escape for the water into the overflow attachment ,b1 in case the rainfall is so heavy as to more than fill the tube4 ,the inside diameter of the overflow attachment is the same as that of the receiver 7#h inches71 as will be seen from the figure4 ,the rain gauge should be firmly set in a wooden frame1 so arranged that the overflow attachment can readily be removed from the frame4 ,the box in which the gauge is sent out by the manufacturer is usually designed to serve as a permanent support when the gauge is set up4 ,the best exposure for the gauge is an open space unobstructed by large trees1 buildings1 or fences4 ,fences1 walls1 or trees should be at a distance from the gauge not less than their own height4 ,if an exposure upon the ground is out of the question1 the gauge may be placed upon a roof1 in which case the middle of a flat unobstructed roof is the best position4 ,records of ,rainfall4----,every rain gauge is provided with a measuring stick1 which is graduated into inches and hundredths4 ,it must be remembered that the amount of rain in the measuring tube is1 by the construction of the ordinary gauge1 ten times greater than the actual rainfall4 ,this fact need not1 however1 be taken into account by the observer1 for the numbers used in graduating the measuring sticks have all been divided by #aj1 and therefore they represent the actual rainfall4 ,the graduations on the stick indicate hundredths of an inch1 and should appear in the record as decimals 74#aj1 4#bj1 etc474 ,ten inches of water in the measuring tube will reach the mark #a4jj on the stick2 thus #a4jj denotes #a inch and zero hundredths of rain4 ,one inch of water in the tube will reach the 4#aj mark1 indicating #aj_/ajj of an inch4 ,the shortest lines on the measuring stick denote successive hundredths of an inch4 ,thus1 if water collected comes to a point halfway between the 4#aj and 4#bj lines1 the amount is 4#ae inch1 and so on4 ,in measuring rainfall1 the stick is lowered through the bottom of the receiver into the measuring tube1 and on being withdrawn the wet portion of the stick at once shows the depth of water in the tube4 ,care must be exercised to put the end of the stick where the numbering begins first into the gauge1 and to pass the stick through the middle of the tube4 ,after each observation the gauge should be emptied and drained1 and immediately put back into place4 ,when the total rainfall more than fills the measuring tube1 i4e41 exceeds #b inches1 the receiver should first be lifted off and the tube removed with great care so as not to spill any water4 ,after emptying the tube1 the surplus water in the overflow attachment must be poured into the measuring tube and measured4 ,the amount of rainfall thus found is to be added to the #b inches contained in the measuring tube in order to give the total rainfall4 ,if any water happens to be spilled during its removal from the overflow attachment1 then the amount in the tube will be less than #b inches1 and it must be carefully measured before the latter is emptied4 ,during the winter season1 in all regions where snow forms the chief part of the precipitation1 the only portion of the rain gauge that need be exposed is the overflow attachment4 ,the snow which falls into the gauge may be measured by first melting the snow and then measuring the water as rainfall4 ,about #aj inches of snow give1 on the average1 #a inch of water1 but the ratio varies very greatly according to the density of the snow4 ,besides the measurement of the melted snow collected in the gauge1 it is customary to keep a record of the depth of snowfall in inches1 as measured by means of an ordinary foot rule or a yardstick1 on some level place where there has been little or no drifting4 ,measurements of rain and snowfall are usually made once a day1 at #h ,p4,m41 and also at the end of every storm4 ,enter the amounts of precipitation in the column of the table headed 8,amount0 and state always whether it is rain or melted snow that you have measured4 ,when there has been no precipitation since the last observation1 an entry of #j4jj should be made in the column of the record book devoted to 8,amount of ,precipitation40 ,when the amount is too small to measure1 the entry ,t 7for ,trace7 should be made4 ,continue your non-instrumental record of the time of beginning and ending of the precipitation as before4 ,whenever it is possible1 keep a record of the total amount of precipitation in each storm1 noting this under 8,remarks40 ,try to answer such questions as are asked in ,chapter ,i with the help of your instrumental record of the rain and snowfall4 ,note what depths of snow in different snowstorms are necessary1 when melted1 to make #a inch of water4 ,the ,mercurial ,barometer4----,air has weight4 ,at sea level this weight amounts to nearly #ae pounds on every square inch of surface4 ,imagine a layer of water1 #cd feet deep1 covering the earth4 ,the weight of this water on every square inch of surface would be the same as the weight of the air4 ,under ordinary circumstances the weight of the air is not noticeable1 because air presses equally in all directions1 and the pressure within a body is the same as that outside of it4 ,on account of this equal pressure in all directions1 we speak of the pressure of the air instead of its weight4 ,the effects of the air pressure may become apparent when we remove the air from a surface4 ,by working the piston of a pump in a well we may remove the pressure on the surface of the water in the tube of the pump4 ,when this is done1 a column of water rises in the tube until the top of this column is about #cd feet above the level of the rest of the water in the well4 ,the pressure of the atmosphere on the water outside of the tube holds up this column of water inside the tube4 ,galileo 7#aefd-afdb7 first taught that the air has weight4 ,his pupil ,torricelli went a step further4 ,torricelli saw that the column of water1 held up by the pressure of the air in the tube of the pump1 must exactly balance a similar column of air1 reaching from the surface of the water in the well to the top of the atmosphere4 ,the column of water1 in other words1 exactly replaces this column of air4 ,while working on this subject1 ,torricelli1 in #afdc1 performed the following experiment4 ,he filled a glass tube1 about #c feet long and closed at one end1 with mercury4 ,after filling the tube1 he put his finger over the open end and inverted the tube over a vessel containing mercury4 ,when the lower end of the tube was below the surface of the mercury in the dish1 he removed his finger4 ,at once the column of mercury fell in the tube until it stood at a height of about #cj inches1 leaving a vacant space of #f inches in the upper part of the tube4 ,this space has since been known as the ,torricellian vacuum4 ,torricelli had proved what he had expected1 viz41 that the height of the column of liquid which replaces and balances an air column of the same size varies with the weight of that liquid4 ,it takes a column of water #cd feet long to balance a similar column of air4 ,it takes a column of mercury only #cj inches long to balance a similar column of air4 ,this1 as ,torricelli correctly explained1 is due to the fact that mercury is so much 7#ac-a_/b times7 heavier than water4 ,the column of water weighs just the same as the column of mercury4 ,each column exactly balances an air column of similar cross-section4 ,the height of the water or of the mercury is a measure of the weight or pressure of the air4 ,the greater the pressure on the surface of the water in the well1 the higher will be the top of the water in the pump4 ,the greater the pressure on the surface of the mercury in the basin1 in the experiment of ,torricelli1 the higher will the mercury column stand in the glass tube4 ,either water or mercury may be used as the liquid in the barometer4 ,otto von ,guericke 7#afjb-afhf71 of ,magdeburg1 constructed a water barometer about #cf feet long1 which he attached to the outside wall of his house4 ,this barometer he used for some months1 and made predictions of coming weather changes by means of it4 ,a water barometer is1 however1 a very unwieldy thing to manage1 on account of the great length of its tube4 ,furthermore1 water barometers cannot be used in any countries where the temperatures fall to freezing4 ,mercury is the liquid universally employed in barometers4 ,it is so heavy that only a small column of it is necessary to balance the atmospheric pressure4 ,therefore a mercurial barometer is portable4 ,further1 mercury does not freeze until the temperature falls to #dj below zero4 ,another name which should be mentioned in connection with the barometer is that of ,blaise ,pascal1 who in #afdh fully confirmed ,torricelli's results4 ,pascal saw that if the mercury column is really supported by the weight of the air1 the height of that column must be less on the summit of a mountain than at the base1 because there is less air over the top of the mountain than at the bottom1 and therefore the weight of the air must be less at the summit4 ,to prove this1 he asked his brother-in-law ,perrier1 who lived at ,clermont1 in ,france1 to carry the ,torricellian tube up the ,puy-de-,dme1 a mountain somewhat over #cejj feet high in ,central ,france4 ,this ,perrier did on ,sept4 #ai1 #afdh1 and he found1 as predicted by ,pascal1 that the mercury fell steadily in the tube as he went up the mountain1 and that at the top of the mountain the column of mercury was over #c inches shorter than at the base4 ,the pressure of the atmosphere is a weather element which1 unlike the other elements already considered1 cannot be observed without an instrument4 ,we cannot1 under ordinary conditions at sea level1 determine by any of our senses whether the pressure is rising or falling1 or is stationary4 ,the pressure on the upper floors of one of our high buildings is shown by a barometer to be considerably lower than it is at the level of the street below1 and yet we notice no difference in our feelings at the two levels4 ,it is only when we ascend far into the air1 as in climbing a high mountain or in a balloon1 that the much-diminished pressure at these great heights perceptibly influences the human body4 ,mountain climbers and aronauts who reach altitudes of #ae1jjj to #bj1jjj feet or more1 usually suffer from headache1 nausea1 and faintness1 which have their cause in the reduced pressure encountered at these heights4 ,illustration3 ,,fig4 #e4 ,the ordinary mercurial barometer in use to-day is1 essentially1 nothing more than the glass tube and vessel of ,torricelli's famous experiment4 ,a simple form of the mercurial barometer is shown in ,fig4 #e4 ,it consists of a glass tube about one-quarter of an inch in inside diameter and about #cf inches long4 ,this tube1 closed at the top and open at the bottom1 is filled with mercury1 the lower1 open end dipping into a cup of mercury known as the cistern4 ,the space above the mercury is a vacuum4 ,the mercury extends inside the tube to a height corresponding to the weight or pressure of the air1 the vertical height of the top of the mercury column above the level of the mercury in the cistern1 in inches and hundredths of an inch1 being the barometer reading4 ,at sea level the normal barometer reading is about #cj inches4 ,there is an opening near the top of the cistern1 at the back of the instrument1 through which the air gains access to the mercury and holds up the mercury column4 ,it will readily be seen that1 as the mercury in the tube rises1 the level of the mercury in the cistern falls1 and vice versa1 so that there is a varying relation between the two levels4 ,in order to have the reading accurate1 it is necessary that the surface of the mercury in the cistern should be just at the zero of the barometer scale when a reading is made4 ,to accomplish this1 the bottom of the cistern consists of a buckskin bag which may be raised or lowered by means of a thumb-screw1 seen at the lower end of the instrument4 ,the level of the mercury may thus be changed and adjusted to the top of a black line1 marked on the outside of the cistern1 and which indicates the zero of the scale4 ,before making a reading1 the surface of the mercury in the cistern must be raised or lowered until it just reaches this black line4 ,then the top of the mercury column will give the pressure of the air4 ,the reading is made on an aluminum scale at the top of the wooden back on which the tube is mounted1 this scale being graduated both on the ,english and on the metric system4 ,this barometer may be hung against the wall of a room4 ,the aneroid barometer 7,greek3 without fluid71 although less desirable in many ways than the mercurial1 is nevertheless a useful instrument for rough observations4 ,the aneroid is not good for careful scientific work1 because its readings are apt to be rather inaccurate4 ,to be of much value in indicating exact pressures1 it should frequently be compared with and adjusted to a mercurial barometer4 ,an ordinary aneroid barometer is shown in ,fig4 #f4 ,illustration3 ,,fig4 #f4 ,in this instrument the changes in atmospheric pressure are measured by their effects in altering the shape of a small metallic box1 known as the vacuum chamber4 ,the upper and lower surfaces of this box are made of thin circular sheets of corrugated ,german silver1 soldered together around their outer edges1 thus forming a short cylinder4 ,from this the air is exhausted1 and it is then hermetically sealed4 ,a strong steel spring1 inside or outside of the vacuum chamber1 holds apart the corrugated surfaces1 which tend to collapse1 owing to the pressure of the external air upon them4 ,an increase or decrease in the air pressure is accompanied by an approach1 or a drawing apart1 of the surfaces of the chamber4 ,these slight movements are magnified by means of levers1 a chain1 and a spindle1 and are made to turn an index hand or pointer on the face of the instrument4 ,the outer margin of the face1 underneath the glass1 is graduated into inches and hundredths1 and the pressure may thus be read at once4 ,as the tension of the steel spring varies with the temperature1 aneroids are usually compensated for temperature by having one of the levers made of two different metals1 e4g41 brass and iron1 soldered together1 or else by leaving a small quantity of air in the vacuum chamber4 ,this air1 when heated1 expands1 and thus tends to compensate for the weaker action of the spring1 due to the higher temperature4 ,at best1 however1 this compensation is but imperfect1 and this fact1 together with the friction of the different parts1 the changes in the spring with age1 and the need of frequent adjustments1 makes aneroids rather inaccurate4 ,they may be adjusted to mercurial barometers by means of a small screw1 whose head may be found on the lower surface of the instrument4 ,the words fair1 stormy1 etc41 which frequently appear on the face of aneroid barometers1 are of little use in foretelling weather changes1 as no definite pressures always occur with the same weather conditions4 ,the instrument should be tapped lightly a few times with the finger before a reading is made4 ,the second pointer1 which is often found in aneroids1 is set by the observer on the position marked by the index hand when he makes his reading4 ,the difference between the pressure marked by this set pointer and that shown by the index hand at the next observation is the measure of the change of pressure in the interval4 ,another column must now be added to the record book 7preferably between the columns devoted to temperature and wind7 to receive the 8,pressure in ,inches and ,hundredths40 ,is the pressure constant 7i4e41 are the readings always the same7 or does it vary8 ,if it varies1 is there any apparent system in the variations8 ,is there a tendency to a daily maximum8 ,to a daily minimum8 ,if so1 about what time do these occur1 respectively8 ,what is the average variation 7in inches and hundredths7 in the course of a day8 ,what is the greatest difference in pressure which you have observed in a day8 ,what is the least8 ,does the pressure seem to vary more or less in the colder months than in the warmer8 ,has the height of the mercury column any relation to the weather8 ,are we likely to have rainy weather with rising barometer8 ,is the velocity of the wind related to the pressure in any way8 ,how8 ,can you make any general rules for weather prediction based on the action of the barometer8 ,what rules8 ,tabulation of ,observations4----,the tables suggested in the preceding chapter can be used unchanged with the simple instruments just described4 ,summary of ,observations4----,at the end of each month summarize your instrumental observations in the following way3---- ,temperature4----,add together all your temperature readings2 divide their sum by the total number of observations of temperature1 and the quotient will give you a sufficiently accurate mean or average temperature for the month in question4 ,it is to be noted that the mean monthly temperatures obtained from these observations will be much more accurate if the thermometer readings are made at #g ,a4,m4 and #g ,p4,m41 at #h ,a4,m4 and #h ,p4,m41 etc41 and the mean of these is taken2 or if the mean is derived from the maximum and the minimum temperatures1 discussed in ,chapter ,,iii4 ,this mean temperature should be written at the bottom of the temperature column1 and marked 8,mean40 ,the mean monthly temperature is one of the important meteorological data in considering the climatic conditions of any place4 ,wind4----,determine the frequency of the different wind directions by counting the total number of times the wind has blown from ,n41 ,,ne41 ,e41 etc41 during the month4 ,the wind which you have observed the greatest number of times is the prevailing wind4 ,it may1 of course1 happen that two or three directions have been observed an equal number of times4 ,the number of calms should also be recorded4 ,rainfall4----,the total monthly precipitation is obtained by adding together all the separate amounts of rainfall noted in your record book1 and expressing the total1 in inches and hundredths1 at the bottom of the rainfall column4 ,you now have the means for comparing one month's rainfall with that of another month1 and of seeing how these amounts vary4 ,examine carefully also your non-instrumental observations4 ,see whether you can draw any general conclusions as to the greater prevalence of cloud1 or of rain or snow1 in one month than in another4 ,did the last month have more high winds than the one before8 ,or than the average8 ,were the temperature changes more sudden and marked8 ,was there more or less precipitation than in previous months8 ,,chapter ,,iii4 ,,advanced ,,instrumental ,,observations4 ,the instruments for more advanced study are the following3 maximum and minimum thermometers1 wet and dry-bulb thermometers1 sling psychrometer1 standard barometer1 thermograph1 barograph1 and anemometer4 ,illustration3 ,,fig4 #g4 ,maximum and minimum thermometers are usually mounted together on a board1 as shown in ,fig4 #g1 the lower one of the two being the maximum1 and the upper the minimum4 ,in the view of the instrument shelter 7,fig4 #b71 these thermometers are seen on the left4 ,the minimum thermometer1 when attached to its support1 is either exactly horizontal or else slopes downward somewhat towards the bulb end1 as shown in ,fig4 #g4 ,these instruments1 as their names imply1 register the highest and the lowest temperatures1 respectively1 which occur during each day of #bd hours4 ,the maximum thermometer is filled with mercury4 ,its tube is narrowed just above the bulb1 in such a way that the mercury passes through the constriction with some difficulty4 ,as the temperature rises1 the mercury1 in expanding1 is forced out from the bulb through this narrow passage4 ,when the temperature falls1 however1 the mercury above this point cannot get back into the bulb1 there being nothing to force it back4 ,the length of the mercury column1 therefore1 remains the same as it was when the temperature was highest1 and the instrument is read by observing the number of degrees indicated by the top1 or right-hand end1 of the mercury column upon the scale4 ,after reading1 the thermometer is set by removing the brass pin upon which the bulb end rests1 and whirling the instrument rapidly around the pin to which its upper end is fastened4 ,by this process the mercury is driven back into the bulb1 past the constriction4 ,care must be taken to stop the thermometer safely while it is whirling4 ,after setting1 the reading of the maximum thermometer should agree closely with that of the ordinary or dry-bulb thermometer4 ,the minimum thermometer is filled with alcohol1 and contains within its tube a small black object1 called the index1 which resembles a double-headed black pin4 ,the instrument is so constructed that this index1 when placed with its upper1 or right-hand end1 at the surface of the alcohol1 is left behind1 within the alcohol1 when the temperature rises4 ,on the other hand1 when the temperature falls1 the index is drawn towards the bulb by the surface cohesion of the alcohol1 the top or right end of the index thus marking the lowest temperature reached4 ,the upper end of the thermometer is firmly fastened1 by means of a screw1 to a brass support1 while the lower end rests upon a notched arm4 ,in setting this instrument1 the bulb end is raised until the index slides along the tube to the end of the alcohol column4 ,the thermometer is then carefully lowered back into the notch just referred to4 ,maximum and minimum thermometers need to be read only once a day1 in the evening4 ,the temperatures then recorded are the highest and lowest reached during the preceding #bd hours4 ,the observation hour is preferably #h ,p4,m41 but if this is inconvenient1 or impracticable1 the reading may be made earlier in the afternoon4 ,the hour1 however1 should be as late as possible1 and should not be varied from day to day4 ,the maximum temperature sometimes occurs in the night4 ,the maximum and the minimum temperatures should be entered every day1 in a column headed 8,maximum and ,minimum ,temperatures10 in your record book4 ,the wet- and dry-bulb thermometers1 together commonly known as the psychrometer 7,greek3 cold measure71 are simply two ordinary mercurial thermometers1 the bulb of one of which is wrapped in muslin1 and kept moist by means of a wick leading from the muslin cover to a small vessel of water attached to the frame 7see ,fig4 #h74 ,the wick carries water to the bulb just as a lamp wick carries oil to the flame4 ,the psychrometer is seen inside the shelter on the right in ,fig4 #b4 ,illustration3 ,,fig4 #h4 ,the air always has more or less moisture in it4 ,even the hot1 dry air of deserts contains some moisture4 ,this moisture is either invisible or visible4 ,when invisible it is known as water vapor1 and is a gas4 ,when visible1 it appears as clouds and fog1 or in the liquid or solid form of rain1 snow1 and hail4 ,the amount of moisture in the air1 or the humidity of the air1 varies according to the temperature and other conditions4 ,when the air contains as much water vapor as it can hold1 it is said to be saturated4 ,its humidity is then high4 ,when the air is not saturated1 evaporation goes on into it from moist surfaces and from plants4 ,water which changes to vapor is said to evaporate4 ,this process of evaporation needs energy to carry it on1 and this energy often comes from the heat of some neighboring body4 ,when you fan yourself on a very hot day in summer1 the evaporation of the moisture on your face takes away some of the heat from the skin1 and you feel cooler4 ,the drier the air on a hot day1 the greater is the evaporation from all moist bodies1 and hence the greater the amount of cooling of the surfaces of those bodies4 ,for this reason a hot day in summer1 when the air is comparatively dry1 that is1 not saturated with moisture1 is cooler1 other things being equal1 than a hot day when the air is very moist4 ,over deserts the air is often so hot and dry that evaporation from the face and hands is very great1 and the skin is burned and blistered4 ,over the oceans1 near the equator1 the air is hot and excessively damp1 so that there is hardly any cooling of the body by evaporation1 and the conditions are very uncomfortable4 ,this region is known as the 8,doldrums40 ,the temperatures that are felt at the surface of the skin1 especially where the skin is exposed1 as on the face and hands1 have been named sensible temperatures4 ,our sense of comfort in hot weather depends on the sensible temperatures4 ,these sensible temperatures are not the same as the readings of the ordinary 7dry-bulb7 thermometer1 because our sensation of heat or cold depends very largely on the amount of evaporation from the surface of the body1 and the temperature of evaporation is obtained by means of the wet-bulb thermometer4 ,wet-bulb readings at the various stations of the ,weather ,bureau are entered on all our daily weather maps4 ,in summer 7,july7 the sensible 7wet-bulb7 temperatures are #bj below the ordinary air temperature in the dry southwestern portion of the ,united ,states 7,nevada1 ,arizona1 ,utah74 ,the mean ,july sensible temperatures there are from #ej to #fe2 while on the ,atlantic coast1 from ,boston to ,south ,carolina1 they are between #fe and #ge4 ,hence over the latter district the temperatures actually experienced in ,july average higher than in the former4 ,unless the air is saturated with water vapor1 the evaporation from the surface of the wet-bulb thermometer will lower the temperature indicated by that instrument below that shown by the dry-bulb thermometer next to it1 from which there is no evaporation4 ,the drier the air1 the greater the evaporation1 and therefore the greater the difference between the readings of the two thermometers4 ,by means of tables1 constructed on the basis of laboratory experiments1 we may1 knowing the readings of the wet and dry-bulb thermometers1 easily determine the dew-point and the relative humidity of the air----important factors in meteorological observations 7see ,chapter ,,xxvi74 ,in winter1 when the temperature is below freezing1 the muslin of the wet-bulb thermometer should be moistened with water a little while before a reading is to be made4 ,the amount of water vapor which air can contain depends on the temperature of the air4 ,the higher the temperature1 the greater is the capacity of the air for water vapor4 ,hence it follows that1 if the temperature is lowered when air is saturated1 the capacity of the air is diminished4 ,this means that the air can no longer contain the same amount of moisture 7invisible water vapor7 as before4 ,part of this moisture is therefore changed1 condensed1 as it is said1 from the condition of water vapor into that of cloud1 fog1 rain1 or snow4 ,the temperature at which this change begins is called the dew-point of the air4 ,the relative humidity of the air is the ratio between the amount of water vapor which the air contains at any particular time and the total amount which it could contain at the temperature it then has4 ,relative humidity is expressed in percentages4 ,thus1 air with a relative humidity of #ej has just half as much water vapor in it as it could hold4 ,it is found that the readings of the wet-bulb thermometer are considerably affected by the amount of air movement past the bulb1 and that in a light breeze1 or in a calm1 the reading does not give accurate results as to the humidity of the general body of air outside the shelter4 ,to overcome this difficulty another form of psychrometer has been devised4 ,the sling psychrometer 7,fig4 #i7 consists simply of a pair of wet and dry-bulb thermometers1 fastened together on a board or a strip of metal1 to the upper part of which a cord with a loop at the end is attached4 ,in this form of psychrometer there is no vessel of water and no wick1 but the muslin cover of the wet-bulb thermometer must be thoroughly wet1 by immersion in water1 just before each observation4 ,the instrument is then whirled around the hand at the rate of about #ab feet a second4 ,after whirling about #ej times1 note the readings1 and then whirl the instrument again1 and so on1 until the wet bulb reaches its lowest reading4 ,the lowest reading of the wet bulb1 and the reading of the dry bulb at the same time1 are the two observations that should be recorded4 ,take care to have the muslin wet throughout each observation1 and in windy weather stand to leeward of the instrument1 so that it may not be affected by the heat of your body4 ,the true reading may be obtained within two or three minutes4 ,illustration3 ,,fig4 #i4 ,make observations with the wet-bulb thermometer or the sling psychrometer as a part of your regular daily weather record4 ,note the temperatures indicated by the wet and dry bulbs1 and1 by means of the table in ,chapter ,,xxvi1 obtain the dew-point and the relative humidity of the air at each observation4 ,enter these data in your record book1 in a column headed 8,humidity10 and subdivided into two columns1 one for the dew-point and one for the relative humidity4 ,illustration3 ,,fig4 #aj4 ,by means of observations with the psychrometer you will be able to answer such questions as the following3---- ,does the relative humidity vary from day to day8 ,has it any relation to the direction of the wind8 ,to the state of the sky8 ,to precipitation8 ,does it show any regular variations during the course of a day8 ,how does a high degree of relative humidity affect you in cold weather8 ,in hot weather8 ,between what limits of percentages does the relative humidity vary8 ,do the changes come gradually or suddenly8 ,are these changes related in any way to the changes in the other weather elements8 ,how do the sensible temperatures vary8 ,in what weather conditions do the sensible temperatures differ most from the air temperatures8 ,in what seasons8 ,compare the sensible temperatures obtained by your own observations with the sensible temperatures at various stations of the ,weather ,bureau1 as given on the daily weather map4 ,are there any fairly regular differences between the sensible temperatures observed at your own station and the ,weather ,bureau stations8 ,standard ,mercurial ,barometer4----,a simple form of barometer has been described in ,chapter ,,ii4 ,the ordinary standard mercurial barometer used by the ,weather ,bureau 7,fig4 #aj7 has the glass tube containing the mercury surrounded by a thin brass covering1 through which openings are cut1 near the top1 on the front and back1 exposing to view the glass tube and the top of the mercury column4 ,on one side of this opening there is a strip of metal1 graduated to inches and tenths or twentieths1 by means of which the height of the barometer is determined4 ,this strip1 for barometers used at or near sea level1 is about #d inches long1 the variations in pressure under normal conditions not exceeding that amount4 ,in addition to this fixed scale there is a small scale1 also graduated1 which may be moved up and down the opening in the enclosing brass case by means of a milled head outside and a small rack and pinion inside the brass case4 ,this movable scale1 known as the vernier from the name of its inventor1 ,vernier1 is an ingenious device1 by means of which more accurate readings of the barometer can be made than is possible with the ordinary fixed scale4 ,a vernier graduated into twenty-five parts enables the observer to make readings accurately to the one-thousandth part of an inch4 ,on the front of the barometer there is a small thermometer1 known as the attached thermometer4 ,the bulb of this thermometer1 concealed within the metal casing of the barometer1 is nearly in contact with the glass tube containing the mercury4 ,the air1 upon whose weight the height of the mercury column depends1 gains access to the top of the cistern through leather joints1 by which the cistern is joined to the glass tube4 ,mercurial barometers of the ,weather ,bureau pattern are best hung in a barometer box1 fastened securely against the wall of a room1 where there is a good light on the instrument and where the temperature is as constant as possible4 ,in all accurate work certain corrections have to be applied to barometer readings to make them strictly comparable4 ,these are3 7#a7 correction for altitude2 7#b7 correction for temperature2 and 7#c7 correction for latitude4 ,the first is necessary because of the fact that the weight of the air decreases upwards1 and a barometer reading on a hill or a mountain is not comparable with one at sea level unless the former has been corrected by the addition of the weight of the column of air between the hill or mountain and sea level4 ,the correction for temperature is rendered necessary by the fact that with increasing temperature the mercury in the barometer tube expands more than the metallic scale1 because mercury is more sensitive to heat1 and unless some allowance is made for this fact1 barometer readings made at high temperatures will show somewhat too high a pressure4 ,the readings of the attached thermometer give the temperature of the mercury and are used in making the corrections for temperature4 ,as gravity varies from a maximum value at the poles to a minimum value at the equator1 barometer readings made at different latitudes are corrected for latitude1 which means that they are reduced to latitude #de1 midway between #j and #ij4 ,the correction is #j4jh at the poles and -#j4jh at the equator4 ,tables for use in correcting barometer readings for altitude and for temperature are given in ,chapter ,,xxvi4 ,illustration3 ,,fig4 #aa4 ,thermograph and ,barograph4----,two instruments of much interest are the self-recording thermometer1 or thermograph1 and the self-recording barometer1 or barograph1 manufactured by ,richard ,brothers of ,paris4 ,in the thermograph 7,fig4 #aa7 there is a brass cylinder around which a sheet of paper is wound1 this paper being divided into two-hour intervals of time and into spaces representing differences of #e or #aj of temperature4 ,the cylinder revolves once in a week1 being driven by clock-work contained within it4 ,the thermometer consists of a flat1 bent1 hollow brass tube containing alcohol1 one end of the tube being fastened to the metallic frame seen at the right of the figure1 and the other end being free to move4 ,with rising temperature1 the liquid in the tube expanding more than the metallic casing1 by reason of its greater sensitiveness to heat1 tends to straighten the tube1 while with falling temperature the elasticity of the tube turns it into a sharper curve4 ,these movements of the free end of the tube are carried through a train of levers and thus magnified4 ,at the end of the last lever is a metallic pen filled with ink1 which rests lightly against the paper on the revolving drum4 ,a rise or fall in temperature is thus recorded by a rise or fall of the pen on the record sheet1 and a continuous curve of temperature is secured4 ,the pen of the thermograph should be frequently adjusted to make the reading of the instrument accord with that of a standard mercurial thermometer1 and care should be taken to have the clock keep good time4 ,these adjustments can readily be made by means of a screw and a regulator1 respectively4 ,the thermograph should be exposed in the instrument shelter with the other thermometers4 ,the sheets should be changed1 the clock wound1 and the pen filled once a week1 preferably on ,monday1 at #h ,a4,m41 or at noon4 ,the continuous records written by a thermograph are a valuable addition to the fragmentary observations which are the result of eye readings of the ordinary thermometer4 ,from the former any omitted thermometer readings may be supplied4 ,the interest of thermograph records may be seen in the following figure 7,fig4 #ab71 in which curves traced under different conditions are reproduced4 ,curve a illustrates a period of clear warming weather at ,nashua1 ,n4 ,h41 ,april #bg-cj1 #ahhi4 ,curve b was traced during a spell of cloudy weather at ,nashua1 accompanying the passage of a ,west ,india hurricane1 ,sept4 #ac-af1 #ahhi4 ,curve c illustrates the change from a time of moderate winter weather to a cold spell 7,nashua1 ,feb4 #bb-be1 #ahhi74 ,curve d exhibits a steady fall of temperature from the night of one day over the next noon to the following night1 during the approach of a winter cold spell 7,nashua1 ,jan4 #ai-ba1 #ahhi74 ,curve e shows a reverse condition1 viz41 a continuous rise of temperature through a night from noon to noon 7,nashua1 ,dec4 #af-ag1 #ahhh74 ,curve f shows the occurrence of a high temperature at night1 caused by warm southerly winds1 followed by cold westerly winds 7,cambridge1 ,mass41 ,nov4 #cj-;,dec4 #a1 #ahij74 ,curve g illustrates the sudden rise of temperature due to the coming of a hot1 dry wind 7chinook7 at ,fort ,assiniboine1 ,mont4 7,jan4 #ai1 #ahib74 ,a study of such records leads to the discovery of many important facts1 which would be completely lost sight of without a continuous record4 ,illustration3 ,,fig4 #ab4 ,the barograph 7,fig4 #ac7 is very similar to the thermograph in general appearance4 ,the essential portion of this instrument consists of a series of six or eight hollow shells of corrugated metal screwed one over the other in a vertical column4 ,these shells are exhausted of air1 and form1 in reality1 an aneroid barometer which is six or eight times as sensitive as the ordinary single-chamber aneroid4 ,the springs for distending the shells are inside4 ,the base of the column being fixed1 the upper end rises and falls with the variations in pressure4 ,the movements of the shells are magnified by being carried through a series of levers1 and1 as in the thermograph1 the motion is finally given to a pen at the end of the long lever4 ,the compensation for temperature is the same as in the ordinary aneroid4 ,a small quantity of air is left in one of the shells to counteract1 by its own expansion at increased temperature1 the tendency of the barometer to register too low on account of the weakening of the springs4 ,the barograph may be placed upon a shelf in the schoolroom1 where it can remain free from disturbance1 and yet where the record may be clearly seen4 ,the general care of the barograph is the same as that of the thermograph4 ,brief instructions concerning the care and adjustments of these instruments are sent out by the makers with each instrument4 ,frequent comparison with a mercurial barometer is necessary1 the adjustment of the barograph being made by turning a screw1 underneath the column of shells1 on the lower side of the wooden case4 ,illustration3 ,,fig4 #ac4 ,barograph records are fully as interesting as those made by the thermograph4 ,the week's record traced on the writer's barograph during a winter voyage from ,punta ,arenas1 ,strait of ,magellan1 to ,corral1 ,chile1 ,aug4 #b-i1 #ahig1 gives a striking picture of the rapid and marked changes of pressure during seven days in the ,south ,pacific ,ocean 7,fig4 #ad74 ,illustration3 ,,fig4 #ad4 ,the following figure 7,fig4 #ae7 presents samples of barograph curves traced at ,harvard ,college ,observatory1 ,cambridge1 ,mass41 during ,feb4 #bb-bh1 #ahhg1 and ,may #ag-bc1 #ahhg4 ,the ,february curve illustrates well the large and irregular fluctuations in pressure1 characteristic of our winter months2 while the ,may curve shows clearly the more even quality of the pressure changes in our summer4 ,the anemometer shown in ,fig4 #af is the most generally used of instruments designed to measure wind velocity4 ,it is known as the ,robinson cup anemometer1 and consists of four hollow hemispherical cups upon arms crossed at right angles1 and all facing the same way around the circle4 ,the cross-arms are fixed upon a vertical axis having an endless screw at its lower end4 ,when the cups move around1 the endless screw turns two dials which register the number of miles traveled by the wind4 ,the ,weather ,bureau pattern of anemometer has the dials mounted concentrically1 the outer dial having #ajj1 and the inner1 #ii divisions4 ,the revolutions of the outer dial are recorded on the inner one1 and in making an observation of the number of miles traveled by the wind1 the hundreds and tens of miles are taken from the inner dial1 and the miles and tenths from the outer one4 ,take from the inner scale the hundreds and tens of miles contained between the zero of that scale and the zero of the outer one4 ,take on the outer scale the miles and tenths of miles contained between the zero of that scale and the index point of the instrument4 ,the sum of these readings is the reading of the instrument at the time of the observation4 ,illustration3 ,,fig4 #ae4 ,illustration3 ,,fig4 #af4 ,wind velocities are recorded in miles per hour4 ,the velocity of the wind at any particular moment is found by noting the number of miles and tenths of miles recorded by the index before and after an interval of one minute1 or of five minutes1 and multiplying this rate by #fj or by #ab as the case may be4 ,this gives the number of miles an hour that the wind is blowing at the time of observation4 ,records of wind velocity 7in miles per hour7 are to be made at each regular observation hour1 and are to be entered in the proper column of the table in your record book4 ,the total wind movement in each #bd hours is to be observed once a day1 always at the same hour1 and is to be entered in its proper column in the record book4 ,the total wind movement for #bd hours is obtained as follows3 ,subtract the reading of the anemometer at #ab noon 7or #h ,a4,m41 or any other hour7 of the preceding day from the reading taken at #ab noon or the corresponding hour of the current day1 and the difference will be the total movement of the wind4 ,when the reading of the anemometer is less than the reading of the preceding day1 #iij miles should be added to it2 and the remainder1 after subtracting the reading of the preceding day1 will be the total wind movement for the #bd hours4 ,thus3 ,to-day's reading #ia miles2 yesterday's reading #iej miles4 ,hence #ia #iij #ajha miles1 #ajha - #iej #aca miles total wind movement for the current day4 ,by means of an electrical attachment the anemometer may be arranged so as to record continuously on a cylinder rotating by clock-work1 a pen making a mark on the paper for every mile traveled by the wind4 ,the anemometer should be exposed on top of a building where there is as little obstruction as possible by tall chimneys1 higher buildings1 and the like4 ,the nephoscope 7,greek3 cloud observer7 is an instrument used in determining the directions of movement of clouds4 ,these directions1 if determined by ordinary eye observation of the clouds as they drift across the sky1 are apt to be quite inaccurate4 ,the best method of observing directions of cloud movement is to note the path of the reflection of the cloud in a horizontal mirror1 the observer looking at this reflection through an eyepiece which remains fixed during the operation4 ,such a horizontal mirror1 adapted to measure the direction of motion of clouds1 is known as a nephoscope4 ,a form of nephoscope devised by ,mr4 ,h4 ,h4 ,clayton1 of ,blue ,hill ,observatory1 ,hyde ,park1 ,mass41 is shown in ,fig4 #ag4 ,illustration3 ,,fig4 #ag4 ,this instrument consists of a circular mirror1 #ac inches in diameter1 sunk in a narrow circular wooden frame1 on top of which is fastened a brass circle1 ,s4,w4,n4,e41 divided to #e of arc4 ,inside of this fixed circle is a movable brass one1 to which is attached a brass arc1 ,,bd1 rising above the mirror and bearing a movable eyepiece1 ,c4 ,this arc forms the quadrant of a circle whose center is the center of the mirror1 and is divided to #e of arc4 ,its top is held vertically over the center of the mirror by two rods fastened to the movable circle4 ,the center of the mirror ,a is marked by cross lines on the reflecting surface1 the glass of which is thin4 ,in order to determine the motion of a cloud1 the movable circle and tripod are revolved until the arc ,,bd is in the vertical plane formed by the cloud1 the center of the mirror1 and the eye4 ,the eyepiece ,c is then shifted until some point of the cloud image1 as seen through the eyepiece1 is projected on the intersection of the cross lines on the glass4 ,the cloud image soon changes its position1 and while the eye is still held at the eyepiece1 a small index is placed on the part of the cloud image which previously appeared on the center of the mirror4 ,if now a ruler be placed on the index and the center of the mirror and extended backward1 its intersection with the divided scale will give the direction from which the cloud came to the nearest degree1 if all the measurements have been accurately made4 ,the height of the cloud above the horizon is found by reading the position of the eyepiece on the divided quadrant4 ,the nephoscope may be placed on a table1 out of doors in fine weather1 or close to a window from which the clouds to be observed can be seen4 ,the instrument must be properly oriented1 so that the four points marked ,n41 ,e41 ,s41 and ,w4 on the frame shall correspond to the four chief compass directions4 ,the zero 7#j7 of the movable brass scale is usually put at the ,s4 ,hence1 if a cloud is found moving from exactly ,,sw41 the angular measurement of its direction of motion will be #de4 ,if a cloud is moving from due ,e41 the angular measurement of its direction of motion will be #bgj4 ,when the sky is completely overcast with a uniform layer of cloud1 it is usually impossible to determine any direction of movement1 because of the difficulty of selecting and keeping in view1 on the mirror1 some particular point of cloud4 ,observations with the nephoscope may be made as often as is desired1 and should be entered in an appropriate column in the record book4 ,tabulation of ,observations4----,a convenient form of table which may be used in the complete instrumental observations is given on the next page4 ,the number of columns and their arrangement may1 of course1 be varied to suit the number and the nature of the records4 ,summary of ,observations4----,in the preceding chapter we have seen how to obtain the mean monthly temperature from the daily observations1 the frequency of the different wind directions for each month1 and the total monthly precipitation4 ,the addition of the new instruments1 the maximum and minimum thermometers1 the psychrometer1 the anemometer1 and the nephoscope1 enables us to obtain the following additional data in our monthly summaries4 ,temperature4----,the mean monthly temperature may be obtained from the maximum and minimum temperatures as follows3 ,add together all the daily maximum and minimum temperatures for a month4 ,divide this sum by the total number of readings you have made of each thermometer 7i4e41 one reading of the maximum and one of the minimum each day1 making two readings a day71 and the result will be the mean monthly temperature derived from the maximum and minimum temperature4 ,this is a more accurate mean temperature than the one noted in the summary of the preceding chapter4 ,add together all the maximum temperatures noted during one month4 ,divide this sum by the number of observations1 and the result gives the mean maximum temperature for the month4 ,,table ,,for ,,meteorological ,,record4 ,,date4 ---------------------------------------- ------------------------------ ,,hour4 ---------------------------------------- ------------------------------ ,,pressure 7in inches74 ---------------------------------------- ----------------------------- ,,dry ,,bulb4 ---------------------------------------- -------------- ,,wet ,,bulb4 ,,temperature4 ---------------------------------------- -------------- ,,max4 ---------------------------------------- -------------- ,,min4 ---------------------------------------- ----------------------------- ,,dew-,,point4 ---------------------------------------- -------------- ,,relative ,,humidity4 ,,humidity4 ---------------------------------------- ----------------------------- ,,direction4 ---------------------------------------- -------------- ,,velocity ,,wind4 7miles per hr474 ---------------------------------------- -------------- ,,total ,,miles ,,per ,,day4 ---------------------------------------- ----------------------------- ,,kind4 ---------------------------------------- -------------- ,,amount 7in tenths74 ---------------------------------------- -------------- ,,direction ,,of ,,clouds4 ,,movement4 ---------------------------------------- -------------- ,,angular ,,altitude ---------------------------------------- ----------------------------- ,,time ,,of ,,beginning ,,and ,,ending4 ---------------------------------------- -------------- ,,kind4 ,,precipitation4 ---------------------------------------- -------------- ,,amount4 ---------------------------------------- ----------------------------- ,,remarks4 ,a similar operation applied to the minimum temperatures gives the mean minimum temperature for the month4 ,in meteorological summaries it is customary also to include the absolute maximum and the absolute minimum temperatures1 i4e41 the highest and lowest single readings of the thermometer made during each month4 ,these can easily be determined by simple inspection of your record book4 ,note also the dates on which the absolute maximum and the absolute minimum occurred4 ,the absolute monthly range of temperature is the difference1 in degrees1 between the absolute maximum and the absolute minimum4 ,humidity4----,the mean relative humidity is obtained by adding together all the different percentages of relative humidity obtained during the month1 and dividing this sum by the whole number of observations of this weather element4 ,wind4----,the mean velocity of the wind corresponding to the different wind directions is readily obtained by adding together all the different velocities 7in miles per hour7 observed in winds from the different directions1 and dividing these sums by the number of cases4 ,the wind summaries will thus give the frequency of the different directions during each month1 and the corresponding mean velocities4 ,the maximum hourly wind velocity is obtained by inspection of the velocity column4 ,the total monthly wind movement is readily deduced from the daily records in the twelfth column of the table on p4 #dd4 ,state of the ,sky4----,in connection with the more advanced records described in this chapter1 the observations of cloudiness should record the number of tenths of the sky cloudy1 as closely as the amount can be estimated by eye1 instead of indicating the state of the sky as cloudy1 fair1 etc4 ,a detailed record of cloudiness in tenths gives opportunity to determine the mean cloudiness for each month1 by averaging1 as in the case of the other means already described4 ,if nephoscope observations are made1 the monthly summary may include the mean direction of cloud movement for each month4 ,this is obtained by adding together all the different angular measurements of directions of cloud movement1 and dividing by the whole number of such observations4 ,by means of your monthly summaries compare one month with another4 ,notice how the means and the extremes of the different weather elements are related2 how they vary from month to month4 ,are there any progressive changes in temperature1 cloudiness1 precipitation1 etc41 from month to month8 ,what are the changes8 ,summarize1 in a short written statement1 the meteorological characteristics of each month as shown by your tables4 ,,part ,,iii4----,,exercises ,,in ,,the ,,construction ,,of ,,weather ,,maps4 ,,chapter ,,iv4 ,,the ,,daily ,,weather ,,map4 ,the first daily weather maps were issued in connection with the ,great ,exhibition of #ahea in ,london4 ,the data were collected by the ,electric ,telegraph ,company and transmitted to ,london over its wires4 ,these maps were published and sold daily 7excepting ,sundays7 from ,aug4 #h to ,oct4 #aa1 #ahea4 ,the first official weather map of the ,united ,states ,weather ,service was prepared in manuscript on ,nov4 #a1 #ahgj1 and on ,jan4 #ad1 #ahga1 the work of manifolding the maps for distribution was begun at ,washington4 ,previous to the publication of this government map1 ,professor ,cleveland ,abbe had issued in ,cincinnati1 with the support of the ,chamber of ,commerce of that city1 the first current weather maps published in the ,united ,states 7,feb4 #bd to ,dec4 #aj1 #ahgj74 ,in ,france1 daily weather maps have been published continuously since ,sept4 #af1 #ahfc4 ,two things are essential for the publication of a daily synoptic weather map2 first1 simultaneous meteorological observations over an extended area2 and1 second1 the immediate collection of these observations by telegraph4 ,the weather map of the ,united ,states is based on simultaneous observations made at about #aej stations in different parts of this country1 besides several coperating stations in ,canada1 ,central ,america1 ,mexico1 and the ,west ,indies4 ,at each of our stations1 whose location may be seen on any weather map1 the ,weather ,bureau employs one or more observers1 who1 twice a day1 at #h ,a4,m4 and #h ,p4,m41 8,eastern ,standard ,time10 make regular observations of the ordinary weather elements1 i4e41 temperature1 pressure1 humidity1 wind direction and velocity1 precipitation1 cloudiness1 etc4 ,the instruments at these stations are all standard1 but the completeness of the equipment varies according to the importance of the station4 ,the #h ,a4,m4 observations are the only ones now generally used in the preparation of weather maps4 ,when the ,weather ,service was first established1 tri-daily charts were for some time issued from the central office in ,washington4 ,on ,april #a1 #ahhh1 the number was reduced to two a day1 and on ,sept4 #cj1 #ahie1 a further change was made1 and now there is but one map a day4 ,the #h ,a4,m4 observations1 as soon as made1 are corrected for certain instrumental errors1 and the barometer readings are reduced to sea level4 ,the data are then put into cipher1 not for secrecy1 but to facilitate transmission and to lessen the chances of error1 and are telegraphed from all parts of the country to the central office of the ,weather ,bureau in ,washington4 ,besides sending their own messages to ,washington1 all the important stations of the ,weather ,bureau receive1 by a carefully devised system of telegraphic circuits1 a sufficient number of the reports from other stations to enable their observers to draw and issue local weather maps4 ,the observations are received at the central office of the ,weather ,bureau in ,washington by special wires1 and are usually all there within an hour after the readings were made4 ,as the messages are received in the forecast room1 they are translated from the cipher back again into the original form1 and the data are entered upon blank maps4 ,the official charged with making the forecasts then draws upon the maps lines of equal temperature1 lines of equal pressure1 lines of equal pressure-change and temperature-change during the past #bd hours4 ,these several sets of lines1 together with those showing the regions of precipitation during the past #bd hours1 furnish the necessary data on which the forecasts can be based4 ,in other words1 the forecast official has before him1 on the several maps1 a bird's-eye view of the weather conditions over the ,united ,states as they were an hour before1 and also of the changes that have taken place in these conditions during the preceding #bd hours4 ,thus1 by knowing the general laws which govern the movements of areas of high and low temperature1 of fair and stormy weather1 across the country1 he can make a prediction as to the probable conditions which any state or section of the country will experience in #ab1 #bd1 or #cf hours4 ,in a later chapter some suggestions will be given for studies of forecasting4 ,the forecasts made in ,washington1 and printed on the ,washington daily weather map1 relate to all sections of the ,united ,states1 and include predictions of cold waves1 killing frosts1 storm winds1 river floods1 and the like1 besides the ordinary changes in weather conditions4 ,these forecasts1 as soon as made1 are at once given to the local newspapers and to the press associations4 ,they are also sent by telegraph to all regular stations of the ,weather ,bureau1 and to all stations at which cautionary or storm signals are to be displayed1 along the ,atlantic or ,gulf coasts1 and on the ,great ,lakes4 ,the ,washington weather map is about #bd by #af inches in size1 and is newly lithographed each day4 ,the total number of maps issued from the central office during the fiscal year ending ,june #cj1 #ahih1 was #caj1bej4 ,in addition to these1 there are now #hd stations of the ,weather ,bureau in different parts of the country1 at which daily weather maps are issued and local forecasts made4 ,these latter forecasts are made by a corps of local forecast officials1 each of whom has to make the weather prediction for his own district4 ,at first1 and until within a few years1 one predicting officer in ,washington made all the forecasts for the country1 but it was found better to have the country divided into geographical sections1 over each one of which the meteorological conditions are fairly similar1 and to have a local forecast official in charge of each section4 ,these local forecast officials have the double advantage of being able to study the weather conditions over the whole country1 as sent them by telegraph each morning1 and also of knowing the special peculiarities of their own regions4 ,this enables them to make more accurate predictions than can be made by an official who may be one or two thousand miles distant1 in ,washington4 ,the greater portion of the maps issued at the map stations outside of ,washington are prepared by what is known as the chalk-plate process1 suggested by ,mr4 ,j4 ,w4 ,smith1 local forecast official at ,boston4 ,this process is as follows3 ,a thin covering of specially prepared chalk1 #a_/h of an inch in thickness1 is spread upon a steel plate of the size of the prospective weather map4 ,on this chalk are engraved1 by means of suitable instruments1 the various weather symbols1 the lines of equal pressure and of equal temperature1 and the wind arrows4 ,the plate is then stereotyped in the ordinary way1 and printed on a sheet prepared for the purpose1 which has a blank outline map of the ,united ,states at the top1 and space in the lower half for the forecasts1 summary1 and tables4 ,the size of the chalk-plate map itself is #aj by #f-a_/b inches2 the size of the whole sheet1 which includes also the text and tables1 #af by #aa inches4 ,weather maps prepared by the chalk-plate process are now issued from #bh of the #hd stations which publish daily maps4 ,at the remaining stations the maps are prepared by a stencil process1 the size of the map being #ac-a_/b by #bb inches4 ,the total number of weather maps issued at the various stations during the fiscal year #ahig-ahih was #e1bci1cjj4 ,besides recording the usual meteorological data1 and publishing weather maps and forecasts1 the various stations of the ,weather ,bureau serve as distributing centers for cold wave1 frost1 flood1 and storm warnings4 ,these warnings are promptly sent out by telegraph1 telephone1 and mail4 ,besides these usual methods of distributing forecasts1 other means have also been adopted4 ,in some places factory whistles are employed to inform those within hearing as to the coming weather2 railway trains are provided with flags1 whose various colors announce to those who are near the train fair or stormy weather1 rising or falling temperature2 and at numerous so-called 8display stations10 scattered all over the country1 the forecasts are widely disseminated by means of flags4 ,,chapter ,v4 ,,temperature4 ,a4 ,lines of ,equal ,temperature4----,temperature is the most important of all the weather elements4 ,it is therefore with a study of the distribution of temperature over the ,united ,states1 and of the manner of representing that distribution1 that we begin our exercises in map drawing4 ,in carrying out the work we shall proceed in a way similar to that adopted by the officials of the ,weather ,bureau in ,washington and at the other map-publishing stations over the country4 ,enter on a blank weather map the temperature readings found in the first column of the table in ,chapter ,,viii4 ,these readings are given in degrees of the ordinary ,fahrenheit scale those which are preceded by the minus sign 7-7 being below zero1 and were made at the same time 7#g ,a4,m41 8,eastern ,standard ,time07 all over the ,united ,states4 ,make your figures small but distinct1 and place them close to the different stations to which they belong4 ,this is done every morning at the ,weather ,bureau in ,washington1 when the telegraphic reports of weather conditions come in from all over the country4 ,when all the temperature readings have been entered on the outline map1 you have before you a view of the actual temperature distribution over the ,united ,states at #g ,a4,m41 on the first day of the series4 ,describe the distribution of temperature in general terms1 comparing and contrasting the different sections of the country in respect to their temperature conditions4 ,where are the lowest temperatures8 ,where are the highest8 ,what was the lowest thermometer reading recorded anywhere on the morning of this day8 ,at what station was this reading made8 ,what was the highest temperature recorded8 ,and at what station was this reading made8 ,notice that the warmest districts on the map are in ,florida1 along the ,gulf ,coast1 and along the coast of ,california4 ,the marked contrasts in temperature between the ,northwest and the ,pacific and ,gulf ,coasts at once suggest a reason why ,florida and ,southern ,california are favorite winter resorts4 ,to these favored districts great numbers of people who wish to escape the severe cold of winter in the ,northern ,states travel every year1 and here they enjoy mild temperature and prevailingly sunny weather4 ,to the cold ,northwest1 on the other hand1 far from the warm waters of the ,pacific1 where the days are short and the sun stands low in the sky1 no seekers after health travel4 ,this annual winter migration from the cities of the ,north to ,florida and ,southern ,california has led to the building of great hotels in favored locations in these ,states1 and during the winter and spring fast express trains1 splendidly equipped1 are run from north to south and from south to north along the ,atlantic ,coast to accommodate the great numbers of travelers between ,new ,york1 ,philadelphia1 ,boston1 ,chicago1 and other large northern cities1 and the ,florida winter resorts4 ,southern ,california also is rapidly developing as a winter resort1 and rivals the far-famed ,riviera of ,southern ,europe as a mild and sunny retreat from the severe climates of the more northern latitudes4 ,the control which meteorological conditions exercise over travel and over habitability is thus clearly shown4 ,florida and ,southern ,california are also regions in which1 owing to the mildness of their winter climates1 certain fruits1 such as oranges and lemons1 which are not found elsewhere in the country1 can be grown out of doors1 and these are shipped to all parts of the ,united ,states4 ,let us take another step in order to emphasize more clearly the distribution of temperature over the ,united ,states on the first day of our series4 ,draw a line which shall separate all places having a temperature above #cj from those having temperatures below #cj1 #cj being nearly the freezing point and1 therefore1 a critical temperature4 ,evidently this will help us to make our description of the temperature distribution more detailed4 ,if this line is to separate places having temperatures above #cj from those having temperatures below #cj1 it must evidently pass through all places whose temperature is exactly #cj4 ,examine the thermometer readings entered on your map to see whether there are any which indicate exactly #cj4 ,you will find this reading at ,norfolk1 ,va41 ,wilmington1 ,s4 ,c41 ,atlanta1 ,ga41 ,chattanooga1 ,tenn41 ,ft4 ,smith1 ,ark41 and ,portland1 ,ore4 ,through all these stations the line of #cj must be drawn4 ,begin the line on the ,atlantic ,coast at ,norfolk1 ,va41 and draw it wherever you find a thermometer reading of #cj4 ,it is best to trace the line faintly with pencil at first1 so that any mistakes can be easily rectified1 and it should be drawn in smooth curves1 not in angles4 ,from ,norfolk the line must run southwest through ,wilmington1 and then westward through ,atlanta1 passing just north of ,augusta1 which has #ca4 ,from ,atlanta the line goes northwest through ,chattanooga1 and thence westward1 curving south of ,memphis 7#bh7 and ,little ,rock 7#bf71 and then northwestward again through ,ft4 ,smith4 ,in fixing the exact position of the #cj line south of ,memphis and ,little ,rock1 the following considerations must be our guide3 ,memphis has #bh2 ,vicksburg has #ce4 ,neither of these stations has #cj4 ,suppose1 however1 that you had started from ,memphis1 with a thermometer1 and had traveled very rapidly to ,vicksburg4 ,the thermometer reading at starting in ,memphis would have been #bh1 and at the end of your journey in ,vicksburg it would have been #ce1 presuming that no change in temperature at either station took place during the journey4 ,evidently the mercury rose during the journey1 and in rising from #bh to #ce it must1 somewhere on the way1 have stood at exactly #cj4 ,now this place1 where the temperature was exactly #cj1 is the point through which our #cj line ought to pass4 ,how are we to determine its location8 ,assume1 as is always done in such cases1 that the temperature increased at a uniform rate between ,memphis and ,vicksburg4 ,the total rise was from #bh to #ce #g4 ,in order to find a temperature #g higher than at ,memphis1 you had to travel the whole distance from ,memphis to ,vicksburg4 ,suppose you had only wished to find a temperature #e higher4 ,then1 assuming a uniform rate of increase between the two stations1 you would have had to travel only #e_/g of the distance1 and your thermometer at that place would have read #bh #e #cc4 ,but assume you had wanted to find the place where the thermometer stood at #cj4 ,in this case you would have been obliged to go but #b_/g of the total distance from ,memphis to ,vicksburg1 and at that point your thermometer reading would have been #bh #b #cj1 which is the point we wish to find4 ,in this way1 then1 when we do not find the exact temperature we are looking for on the map1 we can calculate where that temperature prevails by noting places which have temperatures somewhat higher and somewhat lower1 and proceeding as in the case just described4 ,take another example4 ,little ,rock1 ,ark41 has #bf2 ,shreveport1 ,la41 has #dj4 #dj - #bf #ad1 which is the total difference4 ,from #bf to #cj is #d4 ,therefore a point #d_/ad or #b_/g of the distance from ,little ,rock to ,shreveport should have a temperature of #bf #d #cj1 which is the point we wish to find1 and through which our #cj line must pass4 ,from ,ft4 ,smith the line cannot go north or northwest or west1 because the temperatures there are all below #cj4 ,to the south the temperatures are all above #cj4 ,evidently there is only one direction in which you can prolong the line1 and that is to the southwest4 ,temperatures of #cj cannot be found north of ,el ,paso 7#bh71 because there the temperature distinctly falls1 ,santa ,f having #d1 ,denver1 -#ad1 and ,cheyenne1 -#bc4 ,therefore temperatures above #bh must be found south of ,el ,paso4 ,from ,ft4 ,smith you may1 therefore1 continue the #cj line southwest and west1 passing close to ,el ,paso1 but to the south of it4 ,in determining the further course of the #cj line1 note that ,yuma and all the ,california stations have temperatures above #cj1 while ,winnemucca1 ,nev41 has #ac1 and ,portland1 ,ore41 has exactly #cj4 ,from ,el ,paso you may1 therefore1 continue the line to the northwest1 passing up through ,central ,california parallel with the coast line1 and to the east of all the ,california stations and of ,roseburg1 ,ore41 and thence running through ,portland1 ,ore41 ending just west of ,seattle1 ,wash4 ,notice that the #cj line should be nearer to ,sacramento1 ,cal41 with #cf1 than to ,red ,bluff with #dd4 ,thus you have drawn the line which passes through all places that have a temperature of #cj on the map under discussion4 ,this may be called a line of equal temperature4 ,isotherm1 a compound of two ,greek words meaning equal temperature1 is the name given in meteorology to such lines as this4 ,you have drawn the isotherm of #cj4 ,all parts of the ,united ,states north and east of this line are below #cj1 while all districts south and west of it are above #cj4 ,you see1 therefore1 how much easier the drawing of this one line has made the description of the temperature distribution over the ,united ,states4 ,carry this process a step further by drawing the line which shall pass through all places with a temperature of #dj4 ,this line begins at ,jacksonville1 ,fla4 7#dj71 and runs west1 passing between ,montgomery1 ,ala4 7#cc71 and ,pensacola1 ,fla4 7#df74 ,thence it turns to the northwest1 passing between ,vicksburg1 ,miss4 7#ce71 and ,new ,orleans1 ,la4 7#dh71 and through ,shreveport1 ,la4 7#dj74 ,from ,shreveport it turns to the southwest1 passing to the north and west of ,palestine1 ,tex4 7#df71 and down through ,san ,antonio1 ,tex4 7#dj74 ,its further exact location cannot be determined in ,mexico1 because there are no observations from ,mexican stations1 but the readings at ,yuma1 ,ariz4 7#da71 and at ,san ,diego 7#db71 ,los ,angeles 7#dd71 ,san ,francisco 7#de71 ,red ,bluff 7#dd71 and ,cape ,mendocino 7#dc71 all in ,california1 show that the #dj isotherm may be started again just north of ,yuma1 and may be carried up through ,california1 nearly parallel with the ,pacific ,coast1 ending between ,cape ,mendocino1 ,cal4 7#dc71 and ,roseburg1 ,ore4 7#cg74 ,you have now drawn the isotherms of #cj and of #dj1 and in order to avoid confusion1 mark the ends of the first line #cj and the ends of the second line #dj4 ,isotherms on weather maps are drawn for every even #aj of temperature4 ,they are drawn in smooth curves and not in angular sections4 ,two isotherms cannot cross one another1 for if they did you would have two temperatures1 differing by #aj1 at the point of crossing1 which is obviously impossible4 ,complete the chart for this day by drawing the remaining isotherms1 i4e41 those for #ej1 #bj1 #aj1 #j1 -#aj1 -#bj1 and -#cj1 bearing in mind what has been said in regard to the determination of the positions of isotherms when the exact temperature you are seeking is not given on the map4 ,the dotted lines in ,fig4 #ah show the positions of the isotherms when drawn4 ,notice how clearly the temperature distribution now stands out1 and how simple the description of that distribution has become4 ,observe that the isotherms1 although more or less irregular1 show a good deal of uniformity in their general courses1 and this uniformity is a great assistance in drawing them4 ,study the distribution of temperature on this map1 and the positions of the isotherms1 very carefully4 ,construct isothermal charts for the remaining days of the series4 ,use a new blank map for each day1 and take the temperature observations from the table in ,chapter ,,viii4 ,proceed as in the case of the first day4 ,draw the isotherms for every even #aj of temperature1 taking care to study the course of each line before you begin to draw the line4 ,the charts when completed form a series in which the temperature distribution over the ,united ,states is shown at successive intervals of #bd hours4 ,illustration3 ,,fig4 #ah4----;,isotherms4 ,first day4 ,in order to bring out the temperature distribution on the maps more clearly1 color 7with colored pencils or water colors7 all that portion of each map which lies within the -#bj isotherm a dark blue2 that portion which is between the #j isotherm and the -#bj isotherm a somewhat lighter shade of blue1 and those districts which are between #j and #cj a still lighter blue4 ,the portion of the map above #cj and below #dj may be left uncolored1 while the districts having temperatures over #dj may be colored red4 ,in the map for the third day the district which has temperatures below -#ej should be colored darker blue than any shade used on the other maps1 or black1 in order to emphasize the extremely low temperatures there found4 ,figs4 #ai-bd1 on which the isotherms are shown1 also illustrate the appearance of these maps when the different temperature areas are colored1 as has been suggested4 ,illustration3 ,,fig4 #ai4----,temperature4 ,first ,day4 ,illustration3 ,,fig4 #bj4----,temperature4 ,second ,day4 ,illustration3 ,,fig4 #ba4----,temperature4 ,third ,day4 ,illustration3 ,,fig4 #bb4----,temperature4 ,fourth ,day4 ,illustration3 ,,fig4 #bc4----,temperature4 ,fifth ,day4 ,illustration3 ,,fig4 #bd4----,temperature4 ,sixth ,day4 ,study the maps individually at first4 ,describe the temperature distribution on each map4 ,ask yourself the following questions in each case3 ,where is it coldest8 ,where warmest8 ,what is the lowest temperature on the map8 ,what is the highest8 ,at what stations were these readings made8 ,then compare the successive maps and answer these questions3 ,what changes have taken place in the intervening #bd hours8 ,in what districts has the temperature risen8 ,what is the greatest rise that has occurred8 ,where8 ,in what districts has the temperature fallen8 ,what was the greatest fall in temperature and where did it occur8 ,has the temperature remained nearly stationary in any districts8 ,in which8 ,you will find it a help in answering such questions to make out a table of all the stations1 and to indicate in columns1 after the names of the stations1 the number of degrees of rise or fall in temperature at each place during the #bd-;hour interval between the successive maps4 ,when the temperature is higher at any station than it was on the preceding day1 note this by writing a plus sign 77 before the number of degrees of rise in temperature4 ,when the temperature has fallen1 put a minus sign 7-7 before the number of degrees of fall4 ,thus1 ,new ,orleans1 ,la41 had a temperature of #dh on the first day4 ,on the second it had #cc4 ,therefore the change at ,new ,orleans was -#ae in the #bd hours4 ,at ,key ,west1 ,fla41 the change was #aa in the same time4 ,write a brief account of the temperature distribution on each day of the series1 and of the changes which took place between that day and the one preceding1 naming the districts and ,states over which the most marked falls and rises in temperature occurred1 with some indication of the amount of these changes4 ,note especially the changes in position1 and the extent1 of the districts with temperatures below -#bj2 between #j and -#bj1 and between #cj and #j4 ,write out a clear1 concise statement of the temperature distribution and changes shown on the whole set of six maps4 ,cold ,waves4----,the series of charts for these six days furnishes an excellent illustration of a severe cold wave4 ,a cold wave1 as the term is now used by the ,weather ,bureau1 means1 during ,december1 ,january1 and ,february1 a fall in temperature of from #bj to #af in #bd hours1 with a resulting reduction of temperature to between #j and #cb1 and1 during the months from ,march to ,november inclusive1 a fall of from #bj to #af in #bd hours1 with a reduction of temperature from #af to #cf4 ,during ,december1 ,january1 and ,february a cold wave means the following falls and reductions of temperature4 ,over the ,northwestern ,states1 from western ,wisconsin to ,montana1 including ,wyoming1 ,nebraska1 and western ,iowa1 and over northeastern ,new ,york and northern ,new ,hampshire1 northern ,vermont and northern ,maine1 a fall of #bj or more to zero or below2 over southern ,new ,england and adjoining districts1 the ,lake region1 the central valleys and west to ,colorado1 including northern ,new ,mexico and northwestern ,texas1 a fall of #bj or more to #aj or below2 over southern ,new ,jersey1 ,delaware1 eastern ,maryland1 ,virginia1 western ,north ,carolina1 northwestern ,south ,carolina1 northern ,georgia1 northern ,alabama1 northern ,mississippi1 ,tennessee1 southern ,kentucky1 ,arkansas1 ,oklahoma1 and southern ,new ,mexico1 a fall of #bj or more to #bj or below2 over eastern ,north ,carolina1 central ,south ,carolina1 central ,georgia1 central ,alabama1 central ,mississippi1 central and northern ,louisiana and central and interior ,texas1 a fall of #ah or more to #be or below2 along the ,gulf coasts of ,texas1 ,louisiana1 ,mississippi1 and ,alabama1 over all of ,florida1 and over the coasts of ,georgia and ,south ,carolina1 a fall of #af or more to #cb or below4 ,from ,march to ,november inclusive a cold wave means falls of temperature of the same amounts over the same districts1 with resulting temperatures of #af1 #bd1 #bh1 #cb1 and #cf respectively4 ,notice that the region from which the greatest cold came in this cold wave is ,canada4 ,in that northern country1 with its short days and little sunshine1 and its long1 cold nights1 everything is favorable to the production of very low temperatures4 ,cold waves occur only in winter4 ,in the summer cool spells1 with similar characteristics1 may be called cool waves4 ,cold-,wave ,forecasts4----,a severe cold wave in winter does much damage to fruit and crops growing out of doors in our ,southern ,states1 and to perishable food products in cars1 on the way from the ,south to supply the great cities of the ,north4 ,therefore it is important that warnings should be issued giving early information of the coming cold1 so that farmers and fruit growers and shippers may take every precaution to protect their crops and produce4 ,our ,weather ,bureau takes special pains to study the movements of cold waves and to make forecasts of them1 and so well are the warnings distributed over the country that the fruit growers and the transportation companies1 and the dealers in farm produce1 are able every winter to save thousands of dollars' worth of fruit and vegetables which would otherwise be lost4 ,cold-wave warnings are heeded by many persons besides those who are directly interested in fruits and farm products4 ,the ranchmen in the ,west1 with thousands of cattle under their charge2 the trainmen in charge of cattle trains2 the engineers of large buildings1 such as hotels1 stores1 and office buildings1 who must have their fires hotter in cold weather1----these and many more watch1 and are governed by1 the cold-wave forecasts of our ,weather ,bureau4 ,mean ,annual and ,mean ,monthly ,isothermal ,charts4----,we have thus far considered isothermal charts for the ,united ,states only1 based on the temperature observations made at a single moment of time4 ,it is1 of course1 possible to draw isothermal charts1 the data for which are not the temperatures at a given moment1 but are the mean or average temperatures for a month or a year4 ,such charts have been constructed for other countries besides our own1 as well as for the whole world4 ,an isothermal chart based on the mean annual temperatures is known as a mean annual isothermal chart4 ,these charts show at once the average distribution of temperature for the month or for the year1 just as the ones we have drawn show the distribution of temperature over the ,united ,states at a single moment4 ,b4 ,direction and ,rate of ,temperature ,decrease4 ,temperature ,gradient4----,take your isothermal map for the first day and imagine yourself at ,kansas ,city1 ,mo4 ,in what direction must you go from ,kansas ,city in order to enter most rapidly into colder weather8 ,in what direction must you go from ,kansas ,city in order to enter most rapidly into warmer weather8 ,take the case of ,salt ,lake ,city4 ,in what direction must you go from that station in order to enter most rapidly into colder weather8 ,into warmer weather8 ,what are the corresponding directions in the case of ,spokane1 ,wash48 ,of ,bismarck1 ,n4 ,dak48 ,of ,buffalo1 ,n4 ,y48 ,of ,montreal1 ,que48 ,of ,portland1 ,me48 ,of ,sacramento1 ,cal48 ,draw a line from ,kansas ,city to the nearest point at which there is a temperature #aj lower than at ,kansas ,city4 ,evidently this point is on the isotherm of #j1 and will be found if a line be drawn from ,kansas ,city towards1 and at right angles to1 the isotherm of #j4 ,continue the line beyond the #j isotherm in the direction of still lower temperatures1 i4e41 to the isotherms of -#aj1 -#bj1 and -#cj4 ,beyond the isotherm of -#cj the line must stop4 ,draw similar lines from ,seattle1 ,wash42 ,salt ,lake ,city1 ,utah2 ,denver1 ,col42 ,st4 ,paul1 ,minn42 ,cleveland1 ,o42 and ,new ,york1 ,n4 ,y4 ,prolong these lines all across the map1 so that they will extend from the regions of highest temperature to those of the lowest4 ,a number of intermediate lines may also be added4 ,note that the various directions followed by these lines are square to1 or at right angles to1 the successive isotherms1 and that although the lines all run from higher to lower temperatures1 they do not all trend in the same direction4 ,these lines may be called lines of decrease of temperature4 ,fig4 #be shows a few of these lines of decrease of temperature drawn for the first day4 ,draw similar lines on the other isothermal charts1 for the same stations4 ,are the directions of temperature decrease the same on these charts as on the chart for the first day1 for ,kansas ,city1 ,seattle1 ,salt ,lake ,city1 ,denver1 ,st4 ,paul1 ,cleveland1 ,new ,york8 ,draw lines of decrease of temperature from the following additional stations3 ,key ,west1 ,fla42 ,new ,orleans1 ,la42 ,charleston1 ,s4 ,c42 ,el ,paso1 ,tex42 ,san ,diego1 ,cal42 ,hatteras1 ,n4 ,c4 ,compare the directions of these lines on the different days4 ,how do they change from one day to the next8 ,illustration3 ,,fig4 #be4----,temperature ,gradients4 ,first ,day4 ,next select some line of decrease of temperature on the map for the first day which begins in ,texas1 and follow it northward4 ,where1 along this line1 is the decrease of temperature most rapid8 ,evidently this must be where the isotherms are closest together1 because every isotherm that is crossed means a change of temperature of #aj1 and the more isotherms there are in a given distance1 the more rapidly the temperature is changing4 ,where the isotherms are closest together1 a given decrease of temperature is passed over in the least distance1 or1 conversely1 a greater decrease of temperature is experienced in a given distance4 ,study this question of rapidity or slowness of temperature decrease on the whole series of charts4 ,on which of the charts1 and where1 do you find the most rapid decrease8 ,the slowest decrease8 ,is there any regularity in these rates of temperature decrease either on one map or in the whole series of maps8 ,the term temperature gradient is used by meteorologists to describe the direction and rate of temperature decrease which we have been studying4 ,if we are to compare these rates of temperature change1 we must have some definite scale of measurement4 ,thus1 for example1 in speaking of the wind velocity we say the velocity of the wind is so many miles per hour2 in describing the grade of a railroad we say it is so many feet in a mile4 ,in dealing with these temperature changes1 we adopt a similar scheme4 ,we say3 ,the rate of temperature decrease is so many degrees ,fahrenheit in a distance of one latitude degree 7about #gj miles74 ,in order to make our measurements1 we use a scale of latitude degrees1 just as1 in calculating railroad grades1 we must have a way to measure the miles of track in which the ascent or descent of the roadbed is so many feet4 ,take a strip of paper #f inches long1 with a straight edge1 and lay this edge north and south at the middle of the weather map1 along a longitudinal or meridian line4 ,mark off on the strip of paper the points where any two latitude lines cross the meridian line4 ,these latitude lines are five 7latitude7 degrees apart4 ,therefore divide the space between them on your paper into five divisions1 and each of these will measure just one latitude degree4 ,continue making divisions of the same size until you have ten altogether on the strip of paper4 ,select1 on any weather map1 some station lying between two isotherms at which you wish to measure the rate of temperature decrease4 ,take1 for instance1 ,buffalo1 ,n4 ,y41 on the first day4 ,what you want to find is this3 ,what is the rate of temperature decrease1 or the temperature gradient1 at ,buffalo8 ,lay your paper scale of latitude degrees through ,buffalo1 from the isotherm of #aj to the isotherm of #j1 and as nearly as possible at right angles to the isotherms4#c ,count the number of latitude degrees on your scale between the isotherms of #aj and #j1 on a line running through ,buffalo4 ,there are1 roughly1 about two degrees of latitude in this distance4 ,that is1 in the district in which ,buffalo lies1 the temperature is changing at the rate of #aj ,fahrenheit 7between isotherms #aj and #j7 in two latitude degrees4 ,as our standard of measurement is the amount of change of temperature in one latitude degree1 we divide the #aj 7the number of degrees of temperature7 by the #b 7the number of degrees of latitude71 which gives us #e as the rate of decrease of temperature per latitude degree at ,buffalo1 ,n4 ,y41 at #g ,a4,m41 on the first day of the series4 ,the temperature gradient at ,buffalo is therefore #e4 ,the rule may be stated as follows3 ,select the station for which you wish to know the rate of temperature decrease or temperature gradient4 ,lay a scale of latitude degrees through the station1 and as nearly as possible at right angles to the adjacent isotherms4 ,if the station is exactly on an isotherm then measure the distance from the station to the nearest isotherm indicating a temperature #aj lower4 ,the scale must1 however1 be laid perpendicularly to the isotherm1 as before4 ,divide the number of degrees of difference of temperature between the isotherms 7always #aj7 by the distance 7in latitude degrees7 between the isotherms1 and the quotient is the rate of temperature decrease per latitude degree4 ,or1 to formulate the operation3 ,r ,t _/ ,d1 in which ,r rate2 ,t temperature difference between isotherms 7always #aj71 and ,d distance between isotherms in latitude degrees4 ,thus1 a distance of #aj latitude degrees gives a rate of #a2 a distance of #e gives a rate of #b2 a distance of #b gives a rate of #e2 a distance of #d gives a rate of #b4e1 etc4 ,footnote #c3 ,unless the isotherms are exactly parallel1 the scale cannot be at right angles to both of them4 ,it should1 however1 be placed as nearly as possible in that position4 ,determine the rates of temperature decrease in the following cases3---- ,a4 ,for a considerable number of stations in different parts of the same map1 as for each of the six days of the series4 ,and1 using the school file of weather maps1 ,b4 ,for one station during a winter month and during a summer month1 measuring the rate on each map throughout the month and obtaining an average rate for the month4 ,c4 ,for a station on the ,pacific ,coast1 and one on the ,atlantic ,coast during the same months4 ,d4 ,for a station on the ,gulf of ,mexico1 or in ,florida1 and one in the ,northwest during a winter month4 ,e4 ,for a station in the central ,united ,states1 and one on the ,pacific ,coast1 the ,gulf ,coast1 and the ,atlantic ,coast1 respectively1 during different months of the winter and summer4 ,the determination of the rates of temperature decrease under these different conditions over the ,united ,states prepares us for an appreciation of the larger facts1 of a similar kind1 to be found on the mean annual and mean monthly isothermal charts of various countries1 and also of the whole world4 ,temperature ,gradients on ,isothermal ,charts of the ,globe4----,the mean annual isothermal charts of the globe 7see page #fc7 bring out some very marked contrasts in rates of temperature decrease4 ,thus1 along the eastern side of the ,north ,american continent the isotherms are crowded close together1 while on the western coast of ,europe they are spread far apart4 ,between southern ,florida and ,maine there is the same change in mean annual temperature as is found between the ,atlantic coast of the ,sahara and central ,england4 ,the latter is a considerably longer distance1 and this means that the decrease of temperature is much slower on the ,european ,atlantic coast than on the ,north ,american ,atlantic coast4 ,in fact1 the rate of temperature decrease with latitude in the latter case is the most rapid anywhere in the world1 in the same distance4 ,these great contrasts in temperature which occur within short distances along the eastern coast of ,north ,america have had great influence upon the development of this region1 as has been pointed out by ,woeikof1 an eminent ,russian meteorologist4 ,the products of the tropics and of the ,arctic are here brought very near together2 and at the same time intercommunication between these two regions of widely differing climates is very easy4 ,labrador is climatically an ,arctic land1 and man is there forced to seek his food chiefly in the sea1 for nature supplies him with little on shore1 while southern ,florida is quite tropical in its temperature conditions and in the abundance of its vegetation4 ,between the ,pacific coasts of ,asia and of ,north ,america there is a similar but less pronounced contrast1 the isotherms being crowded together on the eastern coast of ,china and ,siberia1 and being spread apart as they cross the ,pacific ,ocean and reach our ,pacific ,coast4 ,in general1 we naturally expect to find that the temperature decreases as one goes poleward from the equator2 from lower latitudes1 where the sun is always high in the heavens1 to higher latitudes1 where it is near the horizon1 and its warming effect is less4 ,but there are some curious exceptions to this general rule4 ,the lowest temperatures on the ,january isothermal chart 7-#fj7 are found in northeastern ,siberia1 and not1 so far as our observations go1 near the ,north ,pole4 ,if you find yourself at this 8cold pole10 as it is called1 in ,siberia in ,january1 you can reach higher temperatures by traveling north1 south1 east1 or west4 ,in other words1 here is a case of increase of temperature in a northerly direction1 as well as east1 south1 and west4 ,again1 there is a district of high temperature 7#ij7 over southern ,asia in ,july1 from which you can travel south towards the equator and yet reach lower temperatures4 ,in our winter months the contrasts of temperature in the ,united ,states are1 as a rule1 violent1 there being great differences between the cold of the ,northwest and the mild air of ,florida and the ,gulf ,states4 ,in the summer1 on the other hand1 the distribution of temperature is relatively equable1 the isotherms being1 as a rule1 far apart4 ,in summer1 therefore1 we approach the conditions characteristic of the ,torrid ,zone4 ,these are uniformly high temperatures over large areas4 ,the same thing1 on a larger scale1 is seen over the whole ,northern ,hemisphere4 ,during our winter months the isotherms are a good deal closer together than they are during the summer1 or1 in more technical language1 the temperature gradient between the equator and the ,north ,pole is steeper in winter than in summer4 ,,chapter ,,vi4 ,,winds4 ,the observational work already done1 whether non-instrumental or instrumental1 has shown that there is a close relation between the direction of the wind at any station and the temperature at that station4 ,our second step in weather-map drawing is concerned with the winds on the same series of maps which we have thus far been studying from the point of view of temperature alone4 ,in the second column of the table in ,chapter ,,viii are given the wind directions and the wind velocities 7in miles per hour7 recorded at the ,weather ,bureau stations at #g ,a4,m41 on the first day of the series4 ,enter on a blank weather map1 at each station for which a wind observation is given in the table1 a small arrow flying with the wind1 i4e41 pointing in the direction towards which the wind is blowing4 ,make the lengths of the wind arrows roughly proportionate to the velocity of the wind1 the winds of higher velocities being distinguished by longer arrows1 and those of lower velocities by shorter arrows4 ,the letters ,lt4 7 light7 in the table denote wind velocities of #e miles1 or less1 per hour4 ,when you have finished drawing these arrows1 you will have before you a picture of the wind directions and velocities all over the ,united ,states at the time of the morning observation on this day4 7,see solid arrows in ,fig4 #bf47 ,the wind arrows on your map show the wind directions at only a few scattered points as compared with the vast extent of the ,united ,states4 ,we must remember that the whole lower portion of the atmosphere is moving1 and not merely the winds at these scattered stations4 ,it will help you to get a clearer picture of this actual movement of the atmosphere as a whole1 if you draw some additional wind arrows between the stations of observation1 but in sympathy with the observed wind directions given in the table and already entered on your map4 ,these new arrows may be drawn in broken lines1 and may be curved to accord in direction with the surrounding wind arrows4 ,heavier or longer lines may be used to indicate faster winds4 7,see broken arrows1 ,fig4 #bf47 ,illustration3 ,,fig4 #bf4----,winds4 ,first ,day4 ,it is clear that the general winds must move in broad sweeping paths1 changing their directions gradually1 rather than in narrow belts1 with sudden changes in direction4 ,therefore long curving arrows give a better picture of the actual drift of the atmospheric currents than do short1 straight1 disconnected arrows4 ,study the winds on this chart with care4 ,describe the conditions of wind distribution in a general way4 ,can you discover any apparent relation between the different wind directions in any part of the map8 ,is there any system whatever in the winds8 ,write out a brief and concise description of the results of the study of this map4 ,enter on five other blank maps the wind directions given in the table in ,chapter ,,viii for the other five days of the series1 making1 as before1 the lengths of the arrows roughly proportionate to the velocity of the wind1 and adding extra broken arrows as suggested4 7,see ,figs4 #bg-ca47 ,a4 ,study the whole series of six maps4 ,describe the wind conditions on each map by itself1 noting carefully any system in the wind circulation that you may discover4 ,examine the wind velocities also4 ,are there any districts in which the velocities are especially high8 ,have these velocities any relation to whatever wind systems you may have discovered8 ,if so1 include in your description of these systems some consideration of the wind velocities as well as of the wind directions4 ,illustration3 ,,fig4 #bg4----,winds4 ,second ,day4 ,illustration3 ,,fig4 #bh4----,winds4 ,third ,day4 ,illustration3 ,,fig4 #bi4----,winds4 ,fourth ,day4 ,illustration3 ,,fig4 #cj4----,winds4 ,fifth ,day4 ,illustration3 ,,fig4 #ca4----,winds4 ,sixth ,day4 ,b4 ,compare each map of the series with the map preceding it4 ,note what changes in direction and velocity have taken place at individual stations4 ,group these changes as far as possible by the districts over which similar changes have occurred4 ,compare the wind systems on each map with those on the map for the preceding day4 ,has there been any alteration in the position or relation of these systems8 ,write for each day an account of the conditions on that map1 and of the changes that have taken place in the preceding #bd-;hour interval4 ,c4 ,write out a short connected account of the wind conditions and changes illustrated on the whole set of six maps4 ,in the last chapter we studied the progression of the cold wave of low temperatures in an easterly direction across the ,united ,states4 ,notice now the relation of the winds on the successive maps of our series to the movement of the cold wave4 ,place your wind charts and isothermal charts for the six days side by side1 and study them together4 ,the temperature distribution on the second day differs from that on the first4 ,what are the chief differences8 ,examine the wind charts for these two days4 ,do you detect any differences in the wind directions or systems on these days8 ,do these differences help to explain some of the changes in temperature8 ,compare the temperature distribution on the second day with that on the third4 ,what are the most marked changes in the distribution8 ,what changes in the winds on the corresponding wind maps seem to offer an explanation of these variations8 ,proceed similarly with each map of the series4 ,formulate1 in writing1 the general relation between winds and cold waves1 discovered through your study of these charts4 ,cold ,waves in ,other ,countries4----,cold waves in the ,united ,states come1 as has been seen1 from the northwest1 that being the region of greatest winter cold4 ,in ,europe1 cold waves come from the northeast4 ,this is because northwest of ,europe there is a large body of warm water supplied by the ,gulf ,stream drift1 and therefore this is a source of warmth and not of cold4 ,the cold region of ,europe is to the northeast1 over ,russia and ,siberia4 ,cold waves have different names in different countries4 ,in southern ,france the cold wind from the north and northeast is known as the mistral1 derived from the ,latin word magister1 meaning master1 on account of its strength and violence4 ,in ,russia the name buran or purga is given to the cold wave when it blows along with it the fine dry snow from the surface of the ground4 ,this buran is apt to cause the loss of many lives1 both of men and cattle4 ,in the ,argentine ,republic the coolest wind is from the southwest4 ,it is known as a pampero1 from the ,spanish pampa1 a plain4 ,cyclones and ,anticyclones4----,a system of winds blowing towards a common center 7such as is well shown over the ,gulf ,states on the weather map for the second day1 and over the middle ,atlantic coast on the third day7 is called by meteorologists a cyclone4 ,the name was first suggested by ,piddington early in this century4 ,it is derived from the ,greek word for circle1 and hence it embodies the idea of a circular or spiral movement of the winds4 ,a system of outflowing winds1 such as that over the northwestern ,united ,states shown on the maps for the first five days1 and over the western ,gulf ,states on the sixth day is called an anticyclone4 ,this name was proposed by ,galton in #ahfc1 and means the opposite of cyclone4 ,,chapter ,,vii4 ,,pressure4 ,a4 ,lines of ,equal ,pressure3 ,isobars4----,one of the most important weather elements is the pressure of the atmosphere4 ,this has already been briefly discussed in the sections on the mercurial barometer 7,chapter ,,ii74 ,it was there learned that atmospheric pressure is measured by the number of inches of mercury which the weight of the air will hold up in the glass tube of the barometer4 ,our sensation of heat or cold gives us some general idea as to the air temperature4 ,we can tell the wind direction when we know the points of the compass1 and can roughly estimate its velocity4 ,no instrumental aid is necessary to enable us to decide whether a day is clear1 fair or cloudy1 or whether it is raining or snowing4 ,unlike the temperature1 the wind1 or the weather1 the pressure cannot be determined by our own senses without instrumental aid4 ,the next weather element that we shall study is pressure4 ,proceed as in the case of the thermometer readings4 ,enter upon a blank map the barometer readings for the different stations given in the third column of the table in ,chapter ,,viii4 ,when this has been done you have before you the actual pressure distribution over the ,united ,states at #g ,a4,m41 on the first day of the series4 ,describe the distribution of pressure in general terms4 ,where is the pressure highest8 ,where lowest8 ,what are the highest and the lowest readings of the barometer noted on the map8 ,what is the difference 7in inches and hundredths7 between these readings8 ,illustration3 ,,fig4 #cb4----;,isobars4 ,first ,day4 ,draw lines of equal pressure1 following the same principles as were adopted in the case of the isotherms4 ,the latter were drawn for every even #aj of temperature4 ,the former are to be drawn for every even 4#aj inch of pressure4 ,every station which has a barometer reading of an even 4#aj inch will be passed through by some line of equal pressure4 ,philadelphia1 ,pa41 with #bi4ij must be passed through by the #bi4ij line2 ,wilmington1 ,n4 ,c41 with #cj4jj1 must have the #cj4jj line passing through it1 etc4 ,chicago1 with #cj4ag inches1 must lie between the lines of #cj4aj and #cj4bj inches1 and nearer the latter than the former4 ,denver1 ,col41 with #cj4ce inches1 must lie midway between the #cj4cj and #cj4dj lines 7,fig4 #cb74 ,lines of equal pressure are called isobars1 a word derived from two ,greek words meaning equal pressure4 ,describe the distribution of pressure as shown by the arrangement of the isobars4 ,note the differences in form between the isotherms and the isobars4 ,the words high and low are printed on weather maps to mark the regions where the pressure is highest and lowest4 ,draw isobars for the other days1 using the barometer readings given in the table in ,chapter ,,viii4 ,figs4 #cc-ch show the arrangement of the isobars on these days4 ,the pressure charts may be colored1 as indicated by the shading in these figures1 in order to bring out more clearly the distribution of pressure1 according to the same general scheme as that adopted in the temperature charts4 ,color brown all parts of your six isobaric charts over which the pressures are below #bi4ej inches2 color red all parts with pressure above #cj4jj inches4 ,use a faint shade of brown for pressures between #bi4ej inches and #bi4jj inches1 and a darker shade for pressures below #bi4jj inches4 ,in the case of pressures over #cj4jj inches1 use a pale red for pressures between #cj4jj and #cj4ej inches1 and a darker shade of red for pressures above #cj4ej inches4 ,by means of these colors the pressure distribution will stand out very clearly4 ,the scheme of color and shading may1 of course1 be varied to suit the individual fancy4 ,study the isobaric chart of each day of the series by itself at first4 ,describe the pressure distribution on each chart4 ,then compare the successive charts4 ,note what changes have taken place in the interval between each chart and the one preceding2 where the pressures have risen2 where they have fallen1 and where they have remained stationary4 ,write a brief account of the facts of pressure change illustrated on the whole series of six charts4 ,illustration3 ,,fig4 #cc4----,pressure4 ,first ,day4 ,illustration3 ,,fig4 #cd4----,pressure4 ,second ,day4 ,illustration3 ,,fig4 #ce4----,pressure4 ,third ,day4 ,illustration3 ,,fig4 #cf4----,pressure4 ,fourth ,day4 ,illustration3 ,,fig4 #cg4----,pressure4 ,fifth ,day4 ,illustration3 ,,fig4 #ch4----,pressure4 ,sixth ,day4 ,compare the charts of temperature and of pressure1 first individually1 then collectively4 ,what relations do you discover between temperature distribution and pressure distribution on the isothermal and the isobaric charts for the same day8 ,what relations can you make out between the changes in temperature and pressure distribution on successive days8 ,on the whole series of maps8 ,write out the results of your study concisely and clearly4 ,compare the wind charts and the pressure charts for the six days4 ,is there any relation between the direction and velocity of the winds and the pressure8 ,observe carefully the changes in the winds from day to day on these charts1 and the changes in pressure distribution4 ,formulate and write out a brief general statement of all the relations that you have discovered4 ,mean ,annual and ,mean ,monthly ,isobaric ,charts4----,we have thus far been studying isobaric charts based on barometer readings made at a single moment of time4 ,just as there are mean annual and mean monthly isothermal charts1 based on the mean annual and mean monthly temperatures1 so there are mean annual and mean monthly isobaric charts for the different countries and for the whole world1 based on the mean annual and mean monthly pressures4 ,the mean annual and mean monthly isobaric charts of the world show the presence of great oval areas of low and high pressure covering a whole continent1 or a whole ocean1 and keeping about the same position for months at a time4 ,thus1 on the isobaric chart showing the mean pressure over the world in ,january1 there are seen immense areas of high pressure 7anticyclones7 over the two great continental masses of the ,northern ,hemisphere4 ,these anticyclonic areas1 although vastly greater in extent than the small ones seen on the weather maps of the ,united ,states1 have the same system of spirally outflowing winds4 ,over the northeastern portion of the ,north ,pacific and the ,north ,atlantic1 in ,january1 are seen immense areas of low pressure 7cyclones7 with spirally inflowing winds4 ,in ,july the northern continents are covered by cyclonic areas1 and the central portion of the northern oceans by anticyclonic areas4 ,b4 ,direction and ,rate of ,pressure ,decrease3 ,pressure ,gradient4----,in ,chapter ,v we studied the direction and rate of temperature decrease1 or temperature gradient4 ,we saw that the direction of this decrease varies in different parts of the map1 and that the rate1 which depends upon the closeness of the isotherms1 also varies4 ,an understanding of temperature gradients makes it easy to study the directions and rates of pressure decrease1 or pressure gradients1 as they are commonly called4 ,examine the series of isobaric charts to see how the lines of pressure decrease run4 ,draw lines of pressure decrease for the six isobaric charts1 as you have already done on the isothermal charts4 ,when the isobars are near together1 the lines of pressure decrease may be drawn heavier1 to indicate a more rapid rate of decrease of pressure4 ,fig4 #ci shows lines of pressure decrease for the first day4 ,note how the arrangement and direction of these lines change from one map to the next4 ,compare these lines with the lines of temperature decrease4 ,illustration3 ,,fig4 #ci4----,pressure ,gradients4 ,first ,day4 ,next study the rate of pressure decrease4 ,this rate depends upon the closeness of the isobars1 just as the rate of temperature decrease depends upon the closeness of the isotherms4 ,examine the rates of pressure decrease upon the series of isobaric charts4 ,on which charts do you find the most rapid rate8 ,where8 ,on which the slowest8 ,where8 ,do you discover any relation between rate of pressure decrease and the pressure itself8 ,what relation8 ,when expressed numerically1 the barometric gradient is understood to mean the number of hundredths of an inch of change of pressure in one latitude degree4 ,prepare a scale of latitude degrees1 and measure rates of pressure decrease1 just as you have already done in the case of temperature4 ,in this case1 instead of dividing the difference in temperature between the isotherms 7#aj ,t7 by the distance between the isobars 7,d71 we substitute for #aj of temperature 4#aj inch of pressure 7,p74 ,otherwise the operation is precisely the same as described in ,chapter ,v4 ,the rule may be stated as follows3 ,select the station for which you wish to know the rate of pressure decrease or the barometric gradient4 ,lay your scale through the station1 and as nearly as possible at right angles to the adjacent isobars4 ,if the station is exactly on an isobar1 then measure the distance from the station to the nearest isobar indicating a lower pressure4 ,the scale must1 however1 be laid perpendicularly to the isobars1 as before4 ,divide the number of hundredths of an inch of pressure difference between the isobars 7always 4#aj inch7 by the number expressing the distance 7in latitude degrees7 between the isobars2 the quotient is the rate of pressure decrease per latitude degree4 ,or1 to formulate the operation1 ,r ,p _/ ,d1 in which ,r rate2 ,p pressure difference between isobars 7always 4#aj inch71 and ,d distance between the isobars in latitude degrees4 ,determine the rates of pressure decrease in the following cases3---- ,a4 ,for a number of stations in different parts of the same map1 as1 e4g41 ,boston1 ,new ,york1 ,washington1 ,charleston1 ,new ,orleans1 ,st4 ,louis1 ,st4 ,paul1 ,denver1 and on the same day4 ,b4 ,for one station during a winter month and during a summer month1 measuring the rate on each map throughout the month1 and obtaining an average rate for the month4 ,have these gradients at the different stations any relation to the proximity of low or high pressure8 ,to the velocity of the wind8 ,pressure ,gradients on ,isobaric ,charts of the ,globe4----,the change from low pressure to high pressure or vice versa with the seasons1 already noted as being clearly shown on the isobaric charts of the globe1 evidently means that the directions of pressure decrease must also change from season to season4 ,the rates of pressure decrease likewise do not remain the same all over the world throughout the year4 ,if we examine isobaric charts for ,january and ,july1 we shall find that these gradients are stronger or steeper over the ,northern ,hemisphere in the former month than in the latter4 ,,chapter ,,viii4 ,,weather4 ,hitherto nothing has been said about the weather itself1 as shown on the series of maps we have been studying4 ,by weather1 in this connection1 we mean the state of the sky1 whether it is clear1 fair1 or cloudy1 or whether it is raining or snowing at the time of the observation4 ,while it makes not the slightest difference to our feelings whether the pressure is high or low1 the character of the weather is of great importance4 ,the character of the weather on each of the days whose temperature1 wind1 and pressure conditions we have been studying is noted in the table in this chapter4 ,the symbols used by the ,weather ,bureau to indicate the different kinds of weather on the daily weather maps are as follows3 full moon clear2 quarter moon fair1 or partly cloudy2 new moon cloudy2 circle-,r rain2 circle-,s snow4 ,enter on a blank map1 at each station1 the sign which indicates the weather conditions at that station at #g ,a4,m41 on the first day1 as given in the table4 ,when you have completed this1 you have before you on the map a bird's-eye view of the weather which prevailed over the ,united ,states at the moment of time at which the observations were taken4 ,describe in general terms the distribution of weather here shown1 naming the districts or ,states over which similar conditions prevail4 ,following out the general scheme adopted in the case of the temperature and the pressure distribution1 separate1 by means of a line drawn on your map1 the districts over which the weather is prevailingly cloudy from those over which the weather is partly cloudy or clear4 ,in drawing this line1 scattering observations which do not harmonize with the prevailing conditions around them may be disregarded1 as the object is simply to emphasize the general characteristics4 ,enclose also1 by means of another line1 the general area over which it was snowing at the time of observation1 and shade or color the latter region differently from the cloudy one4 ,study the weather distribution shown on your chart4 ,what general relation do you discover between the kinds of weather and the temperature1 winds1 and pressure8 ,proceed similarly with the weather on the five remaining days1 as noted in the table4 ,enter the weather symbols for each day on a separate blank map1 enclosing and shading or coloring the areas of cloud and of snow as above suggested4 ,in ,figs4 #dj-de the cloudy areas are indicated by single-line shading1 and the snowy areas by double-line shading4 ,now study carefully each weather chart with its corresponding temperature1 wind1 and pressure charts4 ,note whatever relations you can discover among the various meteorological elements on each day4 ,then compare the weather conditions on the successive maps4 ,what changes do you note8 ,how are these changes related to the changes of temperature2 of wind2 of pressure8 ,write a summary of the results derived from your study of these four sets of charts4 ,illustration3 ,,fig4 #dj4----,weather4 ,first ,day4 ,illustration3 ,,fig4 #da4----,weather4 ,second ,day4 ,illustration3 ,,fig4 #db4----,weather4 ,third ,day4 ,illustration3 ,,fig4 #dc4----,weather4 ,fourth ,day4 ,illustration3 ,,fig4 #dd4----,weather4 ,fifth ,day4 ,illustration3 ,,fig4 #de4----,weather4 ,sixth ,day4 ,the ,weather of ,temperate and ,torrid ,zones4----,the facts of the presence of clear weather in one region while snow is falling in another1 and of the variability of our weather from day to day in different parts of the ,united ,states1 are emphasized by these charts of weather conditions4 ,this changeableness of weather is a marked characteristic of the greater portion of the ,temperate ,zones1 especially in winter4 ,the weather maps for successive days do not1 as a rule1 show a repetition of the same conditions over extended regions4 ,in the ,torrid ,zone it is different4 ,over the greater part of that zone the regularity of the weather conditions is such that1 day after day1 for weeks and months1 the same features are repeated4 ,there monotony1 here variety1 is the dominant characteristic of the weather4 ,,part ,,iv4----,,the ,,correlations ,,of ,,the ,,weather ,,elements ,,and ,,weather ,,forecasting4 ,,chapter ,,ix4 ,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,pressure4 ,the study of the series of weather maps in ,chapters ,v-,,viii has made it clear that some fairly definite relation exists between the general flow of the winds and the distribution of pressure4 ,we now wish to obtain some more definite result as to the relation of the direction of the wind and the pressure4 ,in doing this it is convenient to refer the wind direction to the barometric or pressure gradient at the station at which the observation is made4 ,the barometric gradient1 it will be remembered1 is the line along which there is the most rapid change of pressure1 and lies at right angles to the isobars 7,chapter ,,vii74 ,illustration3 ,,fig4 #df4 ,take a small piece of tracing paper1 about #c inches square1 and draw upon it a diagram similar to the one here shown4 ,select the station 7between two isobars on any weather map7 at which you intend to make your observation4 ,place the center of the tracing paper diagram over the station1 with the dotted line along the barometric gradient1 the minus end of the line being towards the area of low pressure4 ,observe into which of the four sectors 7marked right1 left1 with1 against7 the wind arrow at the station points4 ,keep a record of the observation4 ,repeat the observation at least #ajj times1 using different stations1 on the same map or on different maps4 ,tabulate your results according to the following scheme1 noting in the first column the date of the map1 in the second1 third1 fourth1 and fifth columns the number of winds found blowing with1 to the right or left of1 and against1 the gradient4 ,,table ,i4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,pressure4 ---------------------------------------- ------ ,,dates ,,with ,,right ,,left ,,against ---------------------------------------- ------ ---------------------------------------- ------ ,sums ---------------------------------------- ------ ,percentages ---------------------------------------- ------ ,at the bottom of each column write down the number of cases in that column1 and then determine the percentages which these cases are of the total number of observations4 ,this is done by dividing the number of cases in each column by the sum-total of all the observations4 ,when you have obtained the percentage of each kind of wind direction1 you have a numerical result4 ,a graphical presentation of the results may be made by laying off radii corresponding in position to those which divide the sectors in ,fig4 #df1 and whose lengths are proportionate to the percentages of the different wind directions in the table4 ,thus1 for a percentage of #bj1 the radii may be made #a inch long1 for #dj1 #b inches1 etc4 ,when completed1 the relative sizes of the sectors will show the relative frequencies of winds blowing in the four different directions with reference to the gradient1 as is indicated in ,fig4 #dg4 ,the ,deflection of the ,wind from the ,gradient3 ,ferrel's ,law4----,the law of the deflection of the wind prevailingly to the right of the gradient is known as ,ferrel's ,law1 after ,william ,ferrel1 a noted ,american meteorologist1 who died in #ahia4 ,the operation of this law has already been seen in the spiral circulation of the winds around the cyclone and the anticyclone1 as shown on the maps of our series4 ,in the case of the cyclone the gradient is directed inward towards the center2 in the case of the anticyclone the gradient is directed outward from the center4 ,in both cases the right-handed deflection results in a spiral whirl1 inward in the cyclone1 outward in the anticyclone4 ,the operation of this law is further seen in the case of the ,northeast ,trade ,winds4 ,these winds blow from about ,lat4 #cj ,n4 towards the equator1 with wonderful regularity1 especially over the oceans4 ,instead of following the gradient and blowing as north winds1 these trades turn to the right of the gradient and become northeast winds1 whence their name4 ,from about ,lat4 #cj ,n4 towards the ,north ,pole there is another great flow of winds over the earth's surface4 ,these winds do not flow due north1 as south winds4 ,they turn to the right1 as do the trades1 and become southwest or west-southwest winds1 being known as the ,prevailing ,westerlies4 ,ferrel's ,law thus operates in the larger case of the general circulation of the earth's atmosphere1 as well as in the smaller case of the local winds on our weather maps4 ,illustration3 ,,fig4 #dg4 ,,chapter ,x4 ,,correlation ,,of ,,the ,,velocity ,,of ,,the ,,wind ,,and ,,the ,,pressure4 ,prepare a scale of latitude degrees1 as explained in ,chapter ,v4 ,select some station on the weather map at which there is a wind arrow1 and at which you wish to study the relation of wind velocity and pressure4 ,find the rate of pressure change per degree as explained in ,chapter ,,vii4 ,note also the velocity1 in miles per hour1 of the wind at the station4 ,repeat the operation #ajj or more times1 selecting stations in different parts of the ,united ,states4 ,it is well1 however1 to include in one investigation either interior stations alone 7i4e41 more than #ajj miles from the coast7 or coast stations alone1 as the wind velocities are often considerably affected by proximity to the ocean4 ,and1 if coast stations are selected1 either onshore or offshore winds should alone be included in one exercise4 ,the investigation may1 therefore1 be carried out so as to embrace the following different sets of operations3---- ,a4 ,interior stations4 ,b4 ,coast stations with onshore winds4 ,c4 ,coast stations with offshore winds4 ,enter your results in a table similar to the one here given3---- ,,table ,,ii4----,,correlation ,,of ,,wind ,,velocity ,,and ,,barometric ,,gradient4 ,for interior 7or coast7 stations1 with onshore 7or offshore7 winds1 in the ,united ,states during the month 7or months7 of ---------------------------------------- -------------------------------- ,rates of ,pressure ,change per ,latitude -#bj #bj-aj #aj-e #e- #c-a_/b- #b-a_/b etc4 ,degree #c-a_/b #b-a_/b -#b ---------------------------------------- -------------------------------- ,distances between ,isobars in ,latitude #j-a_/b #a_/b-a #a-b #b-c #c-d #d-e etc4 ,degrees ---------------------------------------- -------------------------------- ---------------------------------------- -------------------------------- ,wind ,velocities 7miles per hour7 ---------------------------------------- -------------------------------- ,sums ---------------------------------------- -------------------------------- ,cases ---------------------------------------- -------------------------------- ,means ---------------------------------------- -------------------------------- ,the wind velocity for each station is to be entered in the column at whose top is the rate of pressure change found for that station4 ,thus1 if for any station the rate of pressure change is #c-a_/b 7i4e41 4#jc inch in one latitude degree71 and the wind velocity at that station is #ag miles an hour1 enter the #ag in the fourth and fifth columns of the table4 ,when you find that the rate of pressure change for any station falls into two columns of the table1 as1 e4g41 #aj1 or #e1 or #c-a_/c1 then enter the corresponding wind velocity in both those columns4 ,in the space marked ,sums write the sum-total of all the wind velocities in each column4 ,the ,cases are the number of separate observations you have in each column4 ,the ,means denote the average or mean wind velocities found in each column1 and are obtained by dividing the sums by the cases4 ,study the results of your table carefully4 ,deduce from your own results a general rule for wind velocities as related to barometric gradients4 ,the dependence of wind velocities on the pressure gradient is a fact of great importance in meteorology4 ,the ship captain at sea knows that a rapid fall of his barometer means a rapid rate of pressure change1 and foretells high winds4 ,he therefore makes his preparations accordingly1 by shortening sail and by making everything fast4 ,the isobaric charts of the globe for ,january and ,july show that the pressure gradients are stronger 7i4e41 the rate of pressure change is more rapid7 over the ,northern ,hemisphere in ,january than in ,july4 ,this fact would lead us to expect that the velocities of the general winds over the ,northern ,hemisphere should be higher in winter than in summer1 and so they are4 ,observations of the movements of clouds made at ,blue ,hill ,observatory1 ,hyde ,park1 ,mass41 show that the whole atmosphere1 up to the highest cloud level1 moves almost twice as fast in winter as in summer4 ,in the higher latitudes of the ,southern ,hemisphere1 where the barometric gradients are prevailingly much stronger than in the ,northern1 the wind velocities are also prevailingly higher than they are north of the equator4 ,the prevailing westerly winds of the ,southern ,hemisphere1 south of latitude of #cj ,s41 blow with high velocities nearly all the time1 especially during the winter months 7,june1 ,july1 ,august74 ,these winds are so strong from the westward that vessels trying to round ,cape ,horn from the east often occupy weeks beating against head gales1 which continually blow them back on their course4 ,,chapter ,,xi4 ,,form ,,and ,,dimensions ,,of ,,cyclones ,,and ,,anticyclones4 ,a4 ,cyclones4----,provide yourself with a sheet of tracing paper about half as large as the daily weather map4 ,draw a straight line across the middle of it2 mark a dot at the center of the line1 the letter ,n at one end1 and the letter ,s at the other4 ,place the tracing paper over a weather map on which there is a fairly well enclosed center of low pressure 7low71 having the dot at the center of the low1 and the line parallel to the nearest meridian1 the end marked ,n being towards the top of the map4 ,when thus placed1 the paper is said to be oriented4 ,trace off the isobars which are nearest the center4 ,in most cases the #bi4hj-;inch isobar furnishes a good limit1 out to which the isobars may be traced4 ,continue this process1 using different weather maps1 until the lines on the tracing paper begin to become too confused for fairly easy seeing4 ,probably #ae or #bj separate areas of low pressure may be traced on to the paper4 ,it is important to have all parts of the cyclonic areas represented on your tracing4 ,if most of the isobars you have traced are on the southern side of cyclones central over the ,lakes or lower ,st4 ,lawrence1 so that the isobars on the northern sides are incomplete1 select for your further tracings weather maps on which the cyclonic centers are in the central or southern portions of the ,united ,states1 and therefore have their northern isobars fully drawn4 ,when your tracing is finished you have a composite portrait of the isobars around several areas of low pressure4 ,now study the results carefully4 ,draw a heavy pencil or an ink line on the tracing paper1 in such a way as to enclose the average area outlined by the isobars4 ,this average area will naturally be of smaller dimensions than the outer isobars on the tracing paper1 and of larger dimensions than the inner isobars1 and its form will follow the general trend indicated by the majority of the isobars1 without reproducing any exceptional shapes4 ,write out a careful description of the average form1 dimensions measured by a scale of miles or of latitude degrees 7#gj miles #a degree about7 and gradients of these areas of low pressure1 noting any tendency to elongate in a particular direction2 any portions of the composite where the gradients are especially strong1 weak1 etc4 ,b4 ,anticyclones4----,this investigation is carried out in precisely the same manner as the preceding one1 except that anticyclones 7highs7 are now studied instead of cyclones4 ,the isobars may be traced off as far away from the center as the #cj4bj-;inch line in most cases4 ,when1 however1 the pressure at the center is exceptionally high1 it will not be necessary to trace off lower isobars than those for #cj4cj1 or #cj4dj1 or sometimes #cj4ej inches4 ,loomis's ,results as to ,form and ,dimensions of ,cyclones and ,anticyclones4----,one of the leading ,american meteorologists1 ,loomis1 who was for many years a professor in ,yale ,university1 made an extended study of the form and dimensions of areas of low and high pressure as they appear on our daily weather maps4 ,in the cases of areas of low pressure which he examined1 the average form of the areas was elliptical1 the longer diameter being nearly twice as long as the shorter 7to be exact the ratio was #a4id 3 #a74 ,the average direction of the longer diameter he found to be about ,,ne4 7,n4 #cf ,e471 and the length of the longer diameter often #afjj miles4 ,in the case of areas of high pressure1 ,loomis also found an elliptical form predominating2 the longer diameter being about twice as long as the shorter 7ratio #a4ia 3 #a71 and the direction of trend about ,,ne4 7,n4 #dd ,e474 ,these characteristics hold1 in general1 for the cyclonic and anticyclonic areas of ,europe also4 ,the cyclones of the tropics differ considerably from those of temperate latitudes in being nearly circular in form4 ,,chapter ,,xii4 ,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,with ,,their ,,wind ,,circulation4 ,a4 ,cyclones4----,something as to the control of pressure over the circulation of the wind has been seen in the preliminary exercises on the daily weather maps4 ,we now proceed to investigate this correlation further by means of the composite portrait method4 ,this method is a device to bring out more clearly the general systems of the winds by throwing together on to one sheet a large number of wind arrows in their proper position with reference to the controlling center of low pressure4 ,in this way we have many more observations to help us in our investigation than if we used only those which are given on one weather map1 and the circulation can be much more clearly made out4 ,provide yourself with a sheet of tracing paper1 prepared as described in ,chapter ,,xi4 ,place the paper over an area of low pressure on some weather map1 with the dot at the center of the low1 and having the paper properly oriented1 as already explained4 ,trace off all the wind arrows around the center of low pressure1 making the lengths of these arrows roughly proportionate 7by eye7 to the velocity of the wind1 according to some scale previously determined upon4 ,include on your tracing all the wind arrows reported at stations whose lines of pressure-decrease converge towards the low pressure center4 ,repeat this operation1 using other centers of low pressure on other maps1 until the number of arrows on the tracing paper is so great that the composite begins to become confused4 ,be careful always to center and orient your tracing paper properly4 ,select the weather maps from which you take your wind arrows so that the composite shall properly represent winds in all parts of the cyclonic area4 ,deduce a general rule for the circulation and velocity of the wind in a cyclonic area1 as shown on your tracing1 and write it out4 ,b4 ,anticyclones4----,this exercise is done in precisely the same way as the preceding one1 except that anticyclones and their winds are studied instead of cyclones4 ,deduce a general rule for the circulation and velocity of the wind in an anticyclonic area1 as shown on your tracing1 and write it out4 ,the control of the wind circulation by areas of low and high pressure is one of the most important laws in meteorology4 ,buys-,ballot1 a ,dutch meteorologist1 first called attention to the importance of this law in ,europe1 and it has ever since been known by his name4 ,buys-,ballot's ,law is generally stated as follows3 ,stand with your back to the wind1 and the barometer will be lower on your left hand than on your right4#d ,this statement1 as will be seen1 covers both cyclonic and anticyclonic systems4 ,the circulations shown on your tracings hold everywhere in the ,northern ,hemisphere1 not only around the areas of low and high pressure seen on the ,united ,states weather maps1 but around those which are found in ,europe and ,asia1 and over the oceans as well4 ,mention has already been made1 in the chapter on isobars 7,,vii71 of the occurrence of immense cyclonic and anticyclonic areas1 covering the greater portion of a continent or an ocean1 and lasting for months at a time4 ,these great cyclones and anticyclones have the same systems of winds around them that the smaller areas1 with similar characteristics1 have on our weather maps4 ,a further extension of what has just been learned will show that if in any region there comes a change from low pressure to high pressure1 or vice versa1 the system of winds in that region will also change4 ,many such changes of pressures and winds actually occur in different parts of the world1 and are of great importance in controlling the climate4 ,the best-known and the most-marked of all these changes occurs in the case of ,india4 ,during the winter1 an anticyclonic area of high pressure is central over the continent of ,asia4 ,the winds blow out from it on all sides1 thus causing general northeasterly winds over the greater portion of ,india4 ,these winds are prevailingly dry and clear1 and the weather during the time they blow is fine4 ,india then has its dry season4 ,as the summer comes on1 the pressure over ,asia changes1 becoming low2 a cyclonic area replaces the winter anticyclone1 and inflowing winds take the place of the outflowing ones of the winter4 ,the summer winds cross ,india from a general southwesterly direction1 come from over the ocean1 and are moist and rainy4 ,india then has its rainy season4 ,these seasonal winds are known as ,monsoons1 a name derived from the ,arabic and meaning seasonal4 ,footnote #d3 ,in the ,northern ,hemisphere4 ,illustration3 ,,fig4 #dh4 ,the accompanying figure 7,fig4 #dh7 is taken from the ,pilot ,chart of the ,north ,atlantic ,ocean1 published by the ,hydrographic ,office of the ,united ,states ,navy for the use of seamen4 ,it shows the wind circulation around the center of a cyclone which is moving northward along the ,atlantic ,coast of the ,united ,states4 ,the long arrow indicates the path of movement2 the shorter arrows indicate the directions of the winds4 ,by means of such a diagram as this a captain is able to calculate1 with a considerable degree of accuracy1 the position of the center of the cyclone1 and can often avoid the violent winds near that center by sailing away from it1 or by 8lying to10 as it is called1 and waiting until the center passes by him at a safe distance4 ,these cyclones which come up the eastern coast of the ,united ,states at certain seasons are usually violent1 and often do considerable damage to shipping4 ,the ,weather ,bureau gives all the warning possible of the coming of these hurricanes1 as they are called1 by displaying hurricane signals along the coast1 and by issuing telegraphic warnings to newspapers4 ,in this way ship captains1 knowing of the approach of gales dangerous to navigation1 may keep their vessels in port until all danger is past4 ,millions of dollars' worth of property and hundreds of lives have thus been saved4 ,,chapter ,,xiii4 ,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,temperature4 ,it is evident1 from even the most general observation of the weather elements1 that the temperature experienced at any place is very largely dependent upon the direction of the wind4 ,thus1 for instance1 in the ,united ,states1 a wind from some northerly point is likely to bring a lower temperature than a southerly wind4 ,to investigate this matter more closely1 and to discover how the winds at any station during any month are related to the temperatures noted at that station1 we proceed as follows3---- ,select the ,weather ,bureau station at which you wish to study these conditions4 ,note the direction of the wind and the temperature at that station on the first day of any month4 ,prepare a table similar to the following one4 ,,table ,,iii4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,temperature4 ,at 444444444444444444444 during the ,month of 44444444 ---------------------------------------- ------------------------ ,,wind ,,directions ,n4 ,,ne4 ,e4 ,,se4 ,s4 ,,sw4 ,w4 ,,nw4 ---------------------------------------- ---------- ------------------------------------ ------------------------------------ ,,temperatures ------------------------------------ ------------------------------------ ---------------------------------------- ------------------------ ,sums ,total ---------------------------------------- ------------------------ ,cases ,total ---------------------------------------- ------------------------ ,means ,mean ---------------------------------------- ------------------------ ,enter the temperature at #h ,a4,m4 on the first day of the month in a column of the table under the proper wind direction4 ,thus1 if the wind is ,,ne41 and the temperature #db1 enter #db in the second column of the table4 ,repeat the observation for the same station1 and for all the other days of the month1 recording the temperatures in each case in their appropriate columns in the table4 ,omit all cases in which the wind is light1 because winds of low velocities are apt to be considerably affected by local influences4 ,when the observations for the whole month have been entered in the table1 add up all the temperatures in each column 7sums74 ,find the mean temperature 7means7 observed with each wind direction by dividing the sums by the number of observations in each column 7cases74 ,add all the sums together2 divide by the total number of cases1 and the result will be the mean temperature#e for the month at the station4 ,the general effect of the different wind directions upon the temperature is shown by a comparison of the means derived from each column with the mean for the month4 ,footnote #e3 ,derived from the #h ,a4,m4 observations4 ,this does not give the true mean temperature4 ,illustration3 ,,fig4 #di4 ,a graphic representation of the results of this investigation will help to emphasize the lesson4 ,draw1 as in the accompanying figure 7,fig4 #di71 eight lines from a central point1 each line to represent one of the eight wind directions4 ,about the central point describe a circle1 the length of whose radius shall correspond to the mean temperature of the month1 measured on some convenient scale4 ,thus1 if the mean temperature of the month is #ee and a scale of half an inch is taken to correspond to #aj of temperature1 the radius of the circle must be five and a half times half an inch1 or #b-c_/d inches4 ,next lay off on the eight wind lines the mean temperatures corresponding to the eight different wind directions1 using the same scale 7#a_/b in4 #aj7 as in the previous case4 ,join the points thus laid off by a heavy line1 as shown in ,fig4 #di4 ,the figure1 when completed1 gives at a glance a general idea of the control exercised by the winds over the temperatures at the station selected4 ,where the heavy line crosses a wind line inside the circle it shows that the average temperature accompanying the corresponding wind direction is below the mean4 ,when the heavy line crosses any wind line outside the circle1 it shows that the average temperature accompanying the corresponding wind direction is above the mean4 ,such a figure is known as a wind rose4 ,the cold wave and the sirocco are two winds which exercise marked controls over the temperature at stations in the central and eastern ,united ,states4 ,the cold wave has already been described in ,chapter ,v4 ,it is a characteristic feature of our winter weather4 ,it blows down from our ,northwestern ,states or from the ,canadian ,northwest1 on the western side of a cyclone4 ,it usually causes sudden and marked falls in temperature1 sometimes amounting to as much as #ej in #bd hours4 ,the sirocco is a southerly or southwesterly wind4 ,it also blows into a cyclone1 but on its southern or southeastern side4 ,coming from warmer latitudes1 and from over warm ocean waters1 the sirocco is usually a warm wind1 in marked contrast to the cold wave4 ,in winter1 in the ,mississippi ,valley and on the ,atlantic ,coast1 the sirocco is usually accompanied by warm1 damp1 cloudy1 and snowy or rainy weather4 ,the high temperatures accompanying it 7they may be as high as #ej or #fj even in midwinter7 are very disagreeable4 ,our warm houses and our winter clothing become oppressive and we long for the bright1 crisp1 cold weather brought by the cold wave4 ,in summer when a sirocco blows we have our hottest spells4 ,then sunstrokes and prostrations by the heat are most common1 and our highest temperatures are recorded4 ,the word sirocco 7from ,syriacus,syrian7 was first used as the name of a warm southerly wind in ,italy4 ,the cause and the characteristics of the ,italian sirocco and of the ,american sirocco are similar1 and the name may therefore be applied to our wind as well as to the ,italian one4 ,in the ,southern ,hemisphere1 at ,buenos ,ayres1 ,argentine ,republic1 there is a similar contrast between two different winds4 ,the pampero is similar in many respects to our cold wave4 ,it is a dry1 cool1 and refreshing wind1 blowing over the vast level stretches of the ,argentine pampas from the southwest4 ,the norte is a warm1 damp1 depressing northerly wind corresponding to our sirocco4 ,,chapter ,,xiv4 ,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,and ,,their ,,temperatures4 ,a4 ,cyclones4----,it follows from the two preceding exercises that some fairly definite distribution of temperature1 depending upon the wind direction1 should exist around areas of low and high pressure4 ,try to predict1 on the basis of the results obtained in ,chapters ,,xii and ,,xiii1 what this relation of temperatures and cyclones and anticyclones is4 ,then work out the relation independently of your prediction1 by studying actual cases obtained from the weather maps1 as follows3---- ,illustration3 ,,fig4 #ej4 ,prepare a sheet of tracing paper as shown in ,fig4 #ej4 ,the diameter of the circle should be sufficiently large to include within the circle the average area covered by a cyclone on the weather maps4 ,place the tracing paper1 properly divided in accordance with the figure1 over a well-defined area of low pressure on a weather map1 centering and orienting it carefully4 ,take the temperature at the station which lies nearest the center of the figure as the standard4 ,notice the temperatures at all the other stations which fall within the limits of the circle1 and mark down at the proper places on the tracing paper1 the or - departures of these local temperatures from the standard temperature4 ,thus1 if the standard is #cg1 and a station has a temperature of #df1 enter #i at the proper place on your tracing paper4 ,again1 if a certain station has #bd1 enter -#ac at the proper place on the paper4 ,continue this process until your paper has all of its divisions well filled4 ,it is best to select all the maps used in this investigation from the same month1 for in that case the data are more comparable than if different months are taken4 ,when a sufficient number of examples has been obtained1 find the average departure 7 or -7 of the temperatures in each division of the tracing from the central standard temperature4 ,express these averages graphically by means of a wind rose1 as in the last exercise4 ,another ,method4----,the above correlation may be investigated by means of another method1 as follows3---- ,prepare a piece of tracing paper by drawing an ,n4 and ,s4 line upon it1 and placing a dot at the center of the line4 ,lay the paper over an area of low pressure on any weather map1 centering and orienting it properly1 as in the previous exercises4 ,trace off the isotherms which are near the center of low pressure4 ,repeat this process with several maps1 selecting different ones from those used in the first part of this exercise4 ,formulate a rule for the observed distribution of temperature1 and determine the reasons for this distribution4 ,note carefully any effects of the cyclone upon the temperature gradient4 ,b4 ,anticyclones4----,the correlation of anticyclones with their temperatures is studied in precisely the same way as the preceding correlation4 ,both methods suggested in the case of cyclones should be used in the case of anticyclones4 ,when your results have been obtained1 formulate a general rule for the observed distribution of temperature in anticyclones1 and determine the reasons for this distribution4 ,find from your composites the average temperature of cyclones and of anticyclones1 and compare these averages4 ,the unsymmetrical distribution of temperature around cyclones1 which is made clear by the foregoing exercises1 is very characteristic of these storms in our latitudes1 and especially in the eastern ,united ,states4 ,that this has an important effect upon weather changes is evident1 and will be further noted in the chapter on ,weather ,forecasting4 ,the cyclones which begin over the oceans near the equator at certain seasons1 and thence travel to higher latitudes1----tropical cyclones1 so called1----differ markedly from our cyclones in respect to the distribution of temperature around them4 ,the temperatures on all sides of tropical cyclones are usually remarkably uniform1 the isotherms coinciding fairly closely with the isobars4 ,the reason for this is to be found in the remarkable uniformity of the temperature and humidity conditions over the surrounding ocean surface1 from which the inflowing winds come4 ,in the case of our own cyclones1 in the eastern ,united ,states1 the warm southerly wind1 or sirocco1 in front of the center has very different characteristics from those of the cold northwesterly wind1 or cold wave1 in the rear1 as has become evident through the preceding exercise4 ,these winds1 therefore1 naturally show their effects in the distribution of the temperatures in different parts of the cyclonic area4 ,,chapter ,,xv4 ,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,weather4 ,select a file of daily weather maps for some month4 ,commencing with the first map in the set1 observe the weather and the direction of the wind at a considerable number of stations in the same general region 7as1 e4g41 the ,lake region1 the lower ,mississippi ,valley1 the ,pacific ,coast1 etc474 ,enter each case in a table1 similar to ,table ,,iv below1 by making a check in the column under the appropriate wind direction and on a line with the appropriate type of weather4 ,,table ,,iv4----,,correlation ,,of ,,the ,,direction ,,of ,,the ,,wind ,,and ,,the ,,weather4 ,at during the ,month of 4 ---------------------------------------- -------------------------- ,n4 ,,ne4 ,e4 ,,se4 ,s4 ,,sw4 ,w4 ,,nw4 ,,totals,,percentages ---------------------------------------- -------------------------- ,clear ,d ,j ---------------------------------------- -------------------------- ,fair ,f ,k ---------------------------------------- -------------------------- ,cloudy ,g ,l ---------------------------------------- -------------------------- ,rain and ,snow ,h ,m ---------------------------------------- -------------------------- ,totals ,a ---------------------------------------- -------------------------- ,percentages ,b ,c etc4 ---------------------------------------- -------------------------- ,count every observation of rain or snow also as cloudy1 for it usually rains or snows only when the sky is cloudy4 ,continue your observations on all the maps for the month you have chosen4 ,then count up the whole number of cases of clear weather you have found with north winds1 and write down this sum in the first space1 in the column reserved for ,n4 winds4 ,do the same with fair and cloudy weather4 ,add up and enter at the bottom of the column in the space marked ,totals the whole number of observations of clear1 fair1 and cloudy weather you have observed with ,n4 winds4 ,then find what percentage of the weather with ,n4 winds was clear1 and enter this percentage next to the sum of clear weather observations1 in the first division in the column headed ,n4 ,do the same for fair1 cloudy1 and rainy or snowy weather1 deriving the percentages of rain or snow from the total of clear and fair and cloudy4 ,repeat this process of summarizing in every column4 ,your results will then show the percentages of the different kinds of weather noted with the different wind directions4 ,the lower division of the table and the last two columns on the right are to be used for a general summary of the whole investigation4 ,by adding together all the totals of clear1 fair1 and cloudy weather observed with all the eight wind directions you obtain the whole number of observations you have made4 ,enter this in the space marked ,a1 at the right of the table4 ,from this grand total and the total number of observations in each column you may find 7in percentages7 the relative frequencies of the different wind directions4 ,these should be entered under the totals at the bottom of each column1 in the spaces marked ,percentages 7spaces ,b1 ,c1 etc474 ,the total number of observations of clear1 fair1 cloud1 and rain or snow1 noted with all the wind directions1 are to be entered in spaces ,d1 ,f1 ,g1 and ,h1 at the right of the table4 ,from these totals1 and from the grand total in space ,a1 we can determine the relative frequency 7in percentages7 of each kind of weather during the month4 ,these results should be entered in spaces ,j1 ,k1 ,l1 and ,m4 ,study these results carefully4 ,formulate them in a brief written statement4 ,express graphically the following3---- ,a4 ,the percentages of frequency of the different wind directions during the month4 ,b4 ,the percentages of the different kinds of weather noted during the whole month for all wind directions4 ,illustration3 ,,fig4 #ea4 ,a wind rose1 indicating the percentages of frequency of different winds during a month1 or a year1 or several years1 may be constructed as shown in ,fig4 #ea4 ,a certain convenient scale is adopted as representing a frequency of #aj1 and a circle is drawn with this unit as a radius4 ,a second circle1 with a radius twice as long1 represents a frequency of #bj1 and a third circle1 with a radius three times as long1 represents a frequency of #cj4 ,additional circles may be added if necessary4 ,distances corresponding to the different percentages of frequency of the eight wind directions are then laid off along the eight radii of the circles1 and the points thus fixed are joined by a line4 ,the results asked for under question ,b may be plotted as a weather rose on a diagram similar to that above figured4 ,in this case the percentages of frequency of the different varieties of weather 7clear1 fair1 cloudy1 stormy7 may be indicated on the same figure by using different kinds of lines4 ,thus1 a solid line may be employed to represent clear weather2 a broken line for fair2 a broken and dotted line for cloudy2 and a dotted line for stormy weather4 ,,chapter ,,xvi4 ,,correlation ,,of ,,cyclones ,,and ,,anticyclones ,,and ,,the ,,weather4 ,a4 ,cyclones4----,prepare a piece of tracing paper as shown in ,fig4 #eb1 making the diameter of the outer circle about #ajjj miles#f and of the inner circle #ejj miles4 ,place this diagram over a cyclone on any weather map1 centering and orienting it carefully4 ,trace off the weather signs 7indicating clear1 fair1 cloudy1 rain or snow7 around the cyclonic center from the map on to the tracing paper1 taking only observations which are not more than halfway from the cyclonic center to the neighboring anticyclonic center4 ,repeat this process with successive weather maps until the diagram is well filled in all its different divisions4 ,footnote #f3 ,use the scale of miles given on the weather map4 ,a4 ,draw a line on the tracing paper enclosing the average area of cloud 7including rain and snow71 and a second line enclosing the average area of precipitation 7rain or snow74 ,b4 ,determine the percentages of clear1 fair1 cloudy1 and stormy observations for each division of the tracing paper1 i4e41 7a7 for the eight sectors of the large circle2 7b7 for the whole of the small circle2 and 7c7 for the portion of the diagram between the circumference of the inner circle and the circumference of the outer circle4 ,illustration3 ,,fig4 #eb4 ,c4 ,write out in general terms a description of the weather distribution in cyclones as illustrated by your own investigation4 ,b4 ,anticyclones4----,this exercise is done in the same way as the preceding one1 except that anticyclones are substituted for cyclones4 ,the association of fair weather with anticyclones and of stormy weather with cyclones is one of the most important lessons learned from a study of the weather maps4 ,the great areas of high and low pressure control our weather4 ,on land1 where daily weather maps are so easily accessible1 a glance at the map serves in most cases to give a fairly accurate idea of the position and extent of cyclones and anticyclones1 and hence also of the distribution of weather4 ,at sea1 on the other hand1 the navigator has no daily weather maps to refer to1 and his knowledge of the weather conditions which he may expect must be gained from his own observations alone4 ,of these local observations1 the pressure readings are by far the most important4 ,a falling barometer usually means the approach of a cyclone1 with wind1 or storm1 or both4 ,a rising barometer1 on the other hand1 is usually an indication of the fine weather associated with an anticyclone4 ,the unsymmetrical distribution of weather1 characteristic of our cyclones in the ,united ,states1 and also of most cyclones in the ,temperate ,zone1 is associated with their unsymmetrical form1 and the unsymmetrical distribution of their temperature already studied4 ,tropical cyclones have a wonderfully uniform distribution of weather on all sides of their centers1 just as they have a symmetrical form and an even temperature distribution all around them4 ,,chapter ,,xvii4 ,,progression ,,of ,,cyclones ,,and ,,anticyclones4 ,so far no definite study has been made of the changes in the positions of cyclones and anticyclones4 ,if these areas of stormy and fair weather always occupied the same geographic positions1 the different portions of the country would always have the same kinds of weather4 ,a knowledge of the movements of the areas of low and high pressure makes weather forecasting possible4 ,a4 ,cyclones4----,select a set of daily weather maps for a month4 ,turn to the first map of the series4 ,note the position of the center of low pressure1 and indicate this position on a blank weather map of the ,united ,states by marking down a small circle at the proper place4 ,if there are two or more areas of low pressure on the map1 indicate the position of each one of them in a similar way4 ,turn to the second map of the series1 and again enter on the blank map the position of the center of low pressure4 ,connect the two positions of each center by a line4 ,this line may be called the track of the low pressure center4 ,continue this process through the whole set of maps1 connecting all the new positions with the last positions of their respective centers4 ,mark each position with the appropriate date in small1 neat figures4 ,when completed your map will show at a glance the tracks followed by all the cyclones which traveled across the ,united ,states during the month you selected4 ,study these tracks carefully4 ,notice whether there is any prevailing direction in which the cyclones move1 and whether they show any preference for particular paths across the country4 ,can you frame a general rule for the prevailing direction and path of movement8 ,are there any cases which do not accord with the rule8 ,if so1 describe them4 ,in what position1 with reference to the cyclonic tracks during the month you are studying1 is the region in which you are now living8 ,next determine the velocities with which these cyclones moved4 ,prepare a scale of latitude degrees1 as described in ,chapter ,v1 or of miles1 as given at the bottom of the weather map4 ,measure the distances1 in miles1 between the successive positions of all the cyclonic centers4 ,divide these distances by #bd in order to obtain the velocity in miles per hour4 ,what is the highest velocity per hour with which any cyclone moved during the month8 ,what is the lowest8 ,what is the mean1 or average1 velocity8 ,study the tracks and velocities of cyclones in a similar way during several other months4 ,compare the positions of the tracks1 and the velocities of progression1 in summer and winter4 ,b4 ,anticyclones4----,study the tracks and velocities of anticyclones in precisely the same manner4 ,compare the results derived from your investigations in the two cases4 ,cyclonic ,tracks and the ,prevailing ,westerly ,winds4----,the correspondence in the direction of movement of most of our cyclones and of the prevailing westerly winds of the ,northern ,hemisphere 7see ,chapter ,,ix7 will readily be noted4 ,our weather maps show us the atmospheric conditions over the ,united ,states alone1 and we can therefore trace the progression of our cyclones over but a limited area of the ,northern ,hemisphere4 ,an examination of the daily weather maps of the ,north ,atlantic and ,north ,pacific ,oceans1 which are based on observations made on board ships1 and of the weather maps of other countries1 shows us that these atmospheric disturbances which appear on our maps may often be traced for long distances across oceans and lands1 and that they in reality form a great procession across the northern portion of this hemisphere1 and towards and around the ,north ,pole4 ,the average velocity of cyclones in the ,united ,states was carefully determined by ,loomis4 ,his observations show that the mean hourly velocity of cyclones for the entire year is #bh4d miles1 the maximum 7#cd4b miles7 coming in ,february1 and the minimum 7#bb4f miles7 in ,august4 ,over the ,north ,atlantic ,ocean the hourly velocity is #ah miles2 in ,europe1 #af4g miles4 ,the greater velocity of cyclonic movement in the ,united ,states in winter recalls what was said at the close of ,chapter ,x concerning the steeper barometric gradient and the more rapid movement of the whole atmosphere over the ,northern ,hemisphere in winter4 ,,chapter ,,xviii4 ,,sequence ,,of ,,local ,,weather ,,changes4 ,the next1 and last1 step in our study of the correlation of the various weather elements concerns the sequence of weather changes at a station before1 during1 and after the passage of a cyclone and of an anticyclone4 ,a4 ,cyclones4----,i4 ,select some station which the weather maps show to have been directly on the track of a well-developed cyclone1 i4e41 to have been passed over by the center of the cyclone4 ,note the weather conditions at this station1 before1 during1 and after the passage of the storm4 ,tabulate your observations according to the following scheme3---- ,,table ,v4 ,weather ,changes at during 4 ---------------------------------------- -------------------------------- ,,dates ,,pressure ,,temper- ,,wind ,,wind ,,weather ,,direc4 ,,and ,,dist4 ,,ature ,,direction ,,velocity ,,of ,,storm ,,center ---------------------------------------- -------------------------------- ---------------------------------------- -------------------------------- ,in the last column of the table enter the direction and the distance of the cyclonic center from the station1 at each observation4 ,,ii4 ,select a station which was north of the track of a cyclone1 and tabulate 7in a separate table7 the weather conditions at that station before1 during1 and after the passage of the center4 ,,iii4 ,do the same for a station which was south of the track of a cyclone4 ,repeat these observations for several stations4 ,b4 ,anticyclones4----,make a similar series of observations for the passage of an anticyclone centrally over1 north and south of1 several stations4 ,study the sequence of the weather changes shown in the various tables4 ,deduce a general rule for these changes and write it out4 ,,chapter ,,xix4 ,,weather ,,forecasting4 ,in a letter dated at ,philadelphia1 ,july #af1 #agdg1 ,benjamin ,franklin wrote to his friend ,jared ,eliot as follows3 8,we have frequently along the ,north ,american coast storms from the northeast which blow violently sometimes three or four days4 ,of these ,i have had a very singular opinion for some years1 viz43 that1 though the course of the wind is from northeast to southwest1 yet the course of the storm is from southwest to northeast2 the air is in violent motion in ,virginia before it moves in ,connecticut1 and in ,connecticut before it moves at ,cape ,sable1 etc4 ,my reason for this opinion 7if the like have not occurred to you7 ,i will give in my next40 ,in a second letter to the same correspondent1 dated ,philadelphia1 ,feb4 #ac1 #agdi-ej1 ,franklin states his reasons as follows3 8,you desire to know my thoughts about the northeast storms beginning to leeward4 ,some years since1 there was an eclipse of the moon at nine o'clock in the evening1 which ,i intended to observe2 but before night a storm blew up at northeast1 and continued violent all night and all the next day2 the sky thick-clouded1 dark1 and rainy1 so that neither moon nor stars could be seen4 ,the storm did great damage all along the coast1 for we had accounts of it in the newspapers from ,boston1 ,newport1 ,new ,york1 ,maryland1 and ,virginia2 but what surprised us was to find in the ,boston newspapers an account of the observation of that eclipse made there2 for ,i thought as the storm came from the northeast it must have begun sooner at ,boston than with us1 and consequently have prevented such an observation4 ,i wrote to my brother about it1 and he informed me that the eclipse was over there an hour before the storm began4 ,since which time ,i have made inquiries from time to time of travelers1 and observed the accounts in the newspapers from ,new ,england1 ,new ,york1 ,maryland1 ,virginia1 and ,south ,carolina2 and ,i find it to be a constant fact that northeast storms begin to leeward1 and are often more violent there than to windward0 7,sparks's ,life of ,franklin1 ,,vi1 #gi1 #aje1 #ajf74 ,the fact that our northeast storms come from the southwest1 which was first noticed by ,benjamin ,franklin some years before he put the suggestion just quoted in writing1 was one of the great contributions to meteorology made by ,americans4 ,modern weather forecasting essentially depends upon the general eastward movement of cyclones and anticyclones1 with their accompanying weather conditions4 ,the daily weather map shows us the actual condition of the weather all over the ,united ,states at #h ,a4,m41 8,eastern ,standard ,time40 ,the positions of cyclones and of anticyclones2 of areas of clear1 fair1 cloudy or stormy weather1 and of regions of high or low temperatures1 are plainly seen at a glance4 ,these areas of fair and foul weather1 with their accompanying systems of spiralling winds1 move across country in a general easterly direction4 ,knowing something of their direction and rate of movement1 we can determine1 with greater or less accuracy1 their probable positions in #ab1 #bd1 #cf1 or #dh hours4 ,the prediction or foretelling of the weather which may be expected to prevail at any station or in any district is weather forecasting4 ,weather forecasts are usually made on our daily weather maps for #bd hours in advance4 ,it is by no means an easy thing to make accurate weather forecasts4 ,careful study and much practice are required of the forecasters of the ,weather ,bureau before they are permitted to make the official forecasts which are printed on the daily maps and in the newspapers4 ,a simple extension and application of the principles learned through the preceding exercises make it possible for us to forecast coming weather changes in a general way4 ,these suggestions are1 however1 not at all to be considered as a complete discussion of this complicated problem4 ,weather forecasts include the probable changes in temperature1 wind direction and velocity1 and weather4 ,pressure is not included4 ,begin your practice in weather forecasting by considering only the changes that may be expected at your own point of observation1 and at first confine yourself to predicting temperature changes alone4 ,temperature4----,provide yourself with a blank weather map4 ,draw an isotherm east and west across the map1 through your station4 ,draw a few other isotherms all the way across the map1 parallel with the first one1 and so arranged that they will be equal distances apart1 the most northerly one running through northern ,maine and the ,northwestern ,states1 and the most southerly one through southern ,florida and ,texas4 ,recalling what you have already discovered concerning the eastward movement of our weather conditions1 what forecast will you make as to the coming temperatures at your station8 ,add some additional east and west isotherms1 so that there will be twice as many on your map as before4 ,what effect will this change in the temperature distribution on your map have upon the temperature forecast you make for your station8 ,formulate a general rule as to temperature forecasts under the conditions of isothermal arrangement here suggested4 ,on a second blank weather map draw an isotherm through your station inclined from northwest to southeast4 ,draw a few other isotherms parallel to the first1 and each one representing a temperature #aj higher than that indicated by the adjacent isotherm on the east4 ,make a general forecast of the temperature conditions that may be expected at your station1 as to kind of change1 if any2 amount of change1 and rapidity of change4 ,of the isotherms just drawn1 erase every second one2 still1 however1 letting those that are left represent differences of temperature of #aj4 ,what forecast will you now make as to temperature8 ,how does this forecast compare with that just made8 ,now draw twice as many isotherms on your map as you had in the first place1 still letting these lines represent differences of temperature of #aj in each case4 ,make a forecast of the kind1 amount1 and rapidity of temperature change at your station under the conditions represented on this map4 ,how does this forecast compare with the two just made8 ,formulate a general rule governing temperature forecasts in cases of isothermal arrangement such as those here considered4 ,take another blank map4 ,draw through your station an isotherm inclined from northeast to southwest4 ,draw other isotherms parallel to this1 west of your station1 letting each successive isotherm represent a temperature #aj lower than that indicated by the adjacent isotherm on the east4 ,make a temperature forecast for your station under these conditions4 ,diminish and increase the number of isotherms on your map1 as suggested in the preceding example1 making temperature forecasts in each case1 and comparing the three sets of forecasts4 ,formulate a general rule for temperature forecasts made under these systems of isotherms4 ,make temperature forecasts from the daily weather maps for your own station1 using the knowledge that you have already gained as to the progression of cyclones and anticyclones 7,chapter ,,xvii71 and as to the temperature distribution in these areas 7,chapter ,,xiv71 to help you in this work4 ,study each day's map carefully before you decide on what you will say4 ,then write out your own forecast1 and afterwards compare your forecast with that made by the ,weather ,bureau4 ,note also1 by reference to your own instrumental observations1 whether the succeeding temperature conditions are such as you predicted4 ,wind ,direction4----,the weather maps already studied taught us that our winds habitually move in spirals4 ,the composite picture of the wind circulation around cyclones and anticyclones 7,chapter ,,xii7 further emphasized this important fact4 ,evidently this law of the systematic circulation of the winds around centers of low and high pressure may be utilized in making forecasts of wind direction4 ,applying the knowledge already gained concerning cyclonic and anticyclonic wind circulations1 ask yourself what winds a station should have which is within the range of the cyclonic wind system1 and is in the following positions with reference to the center3 northeast1 north1 northwest1 east1 at the center1 west1 southeast1 south1 southwest4 ,ask yourself precisely the same questions with reference to a station within an anticyclonic wind system4 ,write out a general rule for the kinds of wind changes which may be expected to take place under these different conditions4 ,when a station is south of the track of a passing cyclone its winds are said to veer1 and the change in the direction of its winds is called veering4 ,a station north of the track of a passing cyclone has a change of direction in its winds which is known as backing1 the winds themselves being said to back4 ,wind ,velocity4----,what general relation between wind velocities and areas of low and high pressure did you discover in your study of the weather maps8 ,what was the result of your work on the correlation of the velocity of the wind and the barometric gradient in ,chapter ,x8 ,and what general statement as to the relation between the velocity of the wind and its distance from a cyclonic or anticyclonic center may be made as the result of your work in ,chapter ,,xii1 on the correlation of cyclones and anticyclones with their wind circulation8 ,these results must be borne in mind in making predictions of coming changes in wind velocities4 ,forecasts of wind velocities are made in general terms only1----light1 moderate1 fresh1 brisk1 high1 gale1 hurricane1----and are not given in miles per hour4 ,make forecasts of wind direction and velocity from the daily weather maps for your own station4 ,continue these for a week or two1 keeping record of the verification or non-verification of each of your forecasts4 ,then make daily forecasts of temperature and of wind direction and velocity together4 ,write out your own forecast for each day before you compare it with the official forecast1 and if the two differ1 keep note of which one seemed to you to be the most accurate4 ,weather4----,what general relation between kind of weather and cyclones and anticyclones was illustrated on the six maps of our series8 ,what is the average distribution of the different kinds of weather around cyclones and anticyclones1 as shown by your composites8 7,chapter ,,xvi47 ,what changes in weather will ordinarily be experienced at a station as a cyclone approaches1 passes over1 and moves off8 ,what conditions will prevail in an anticyclone8 ,make a series of daily forecasts for your own station of probable weather changes1 omitting temperature and winds at first4 ,include in your weather forecasts the state of the sky 7clear1 fair1 cloudy72 the changes in the state of the sky 7increasing or decreasing cloudiness72 the kind of precipitation 7rain or snow7 and the amount of precipitation 7light or heavy74 ,write out your forecasts2 compare them with the official forecasts1 and notice how fully they are verified4 ,then add temperature and winds to your forecasts so that you will make a complete prediction of probable changes in temperature 7kind1 amount1 and rapidity of change71 wind 7direction and velocity71 and weather4 ,practice making these complete forecasts for several weeks1 if time allows4 ,use all the knowledge that you have gained in the preceding work to aid you in this4 ,study each weather map very carefully4 ,do not write down your forecast until you are sure that you have done the best you can4 ,illustration3 ,,fig4 #ec4 ,vary this exercise by extending your forecasts so as to embrace the whole section of country in which your station is situated 7as1 e4g41 ,new ,england1 the ,gulf ,states1 the ,lake region74 ,pay special attention to making forecasts of cold waves1 of heavy rain or snowstorms1 of high winds over the lakes or along the ,atlantic coast1 etc4 ,when possible1 obtain from the daily newspapers any particulars as to damage done by frost or gales1 or concerning snow blockades1 floods due to heavy rains1 etc4 ,fig4 #ec summarizes what has thus far been learned as to the distribution of the various weather elements around a well-developed center of low pressure4 ,the curved broken lines represent the isotherms 7,chapter ,,xiv74 ,the solid concentric oval lines are the isobars 7,chapter ,,xi74 ,the arrows represent the winds1 the lengths of the arrows being roughly proportionate to the wind velocities 7,chapter ,,xii74 ,the whole shaded area represents the region over which the sky is covered by heavy lower clouds4 ,the smaller shaded area1 within the larger1 encloses the district over which rain or snow is falling 7,chapter ,,xvi74 ,the lines running out in front of the cloudy area represent the light upper clouds 7cirrus and cirro-stratus7 which usually precede an area of low pressure4 ,imagine this whole disturbance moving across the ,united ,states in a northeasterly direction1 and imagine yourself at a station 7#a7 directly in the path of the cyclone2 7#b7 south of the track2 and 7#c7 north of the track4 ,in the first case1 as the disturbance moved on in its path1 you would successively occupy the positions marked ,a1 ,b1 and ,c on the line ,,ac1 passing through the center of the cyclone4 ,in the second case you would be first at ,d1 then at ,e1 and then at ,f4 ,in the third case you would be at ,g1 ,h1 and ,j in succession4 ,what changes of weather would you experience in each of these positions as the cyclone passed by you8 ,imagine yourself at some station halfway between the lines ,,ac and ,,df4 ,what weather changes would you have in that position with reference to the storm track8 ,in what respects would these weather changes differ from those experienced along the line ,,df8 ,imagine your station halfway between the lines ,,ac and ,,gj4 ,what weather changes would you have there8 ,how would these changes differ from those experienced along the line ,,gj8 ,it must be remembered that ,fig4 #ec is an ideal diagram4 ,it represents conditions which are not to be expected in every cyclone which appears on our weather maps4 ,if all cyclones were exactly alike in the weather conditions around them1 weather forecasting would be a very easy task4 ,but cyclones are not all alike----far from it4 ,some are well developed1 with strong gradients1 high winds1 extended cloud areas1 heavy precipitation1 and decided temperature contrasts4 ,others are but poorly developed1 with weak gradients1 light winds1 small temperature differences1 and it may be without any precipitation whatever4 ,some cover immense districts of country2 others are small and affect only a limited area4 ,it therefore becomes necessary to examine the characteristics of each approaching cyclone1 as shown on the daily weather map1 very carefully4 ,notice whether it is accompanied by heavy rain or snow2 whether its winds are violent2 how far ahead of the center the cloudy area extends2 how far behind the outer cloud limit the rain area begins2 what is the position of the cloud and rain area with reference to the center1 and other points of equal importance1 and govern yourself1 in making your forecast1 according to the special features of each individual cyclone4 ,well-developed cyclones will be accompanied by marked weather changes4 ,weak cyclones will have their weather changes but faintly marked4 ,the distance of your station from the center of the cyclone is of great importance in determining what the weather conditions and changes shall be1 as may easily be seen by examining ,fig4 #ec4 ,if the storm passes far to the north or far to the south of your station1 you may notice none of its accompanying weather conditions1 except1 perhaps1 a bank of clouds on your horizon4 ,you may for a few hours be under the cloudy sky of some passing storm1 and yet not be reached by its rainy area4 ,the shifts in the wind may be marked and the wind velocities high1 or the expected veering or backing may hardly be noticeable1 owing to the weakness or the distance of the controlling cyclone4 ,again1 the rapidity with which weather conditions will change depends upon the rate of movement of the cyclone itself4 ,the better developed the cyclone1 the higher its velocity of progression1 and the nearer its track lies to the station1 the more emphatic and the more rapid are the weather changes it causes4 ,on the other hand1 the weaker the cyclone1 the slower its rate of progression1 and the further away its track1 the less marked and the slower the weather changes4 ,the probable track of a coming storm1 and its probable rate of movement1 therefore1 need careful study if our forecasts are to be reliable4 ,there are many other obstacles in the way which combine to render weather forecasting extremely difficult4 ,some of these difficulties you will learn to overcome more or less successfully by the experience you will gain from a careful and persevering study of the daily weather maps2 others1 the best forecast officials of our ,weather ,bureau have not yet entirely overcome4 ,the tracks followed by our cyclones vary more or less from month to month1 and even if the average tracks for each month are known1 individual cyclones may occur which absolutely disregard these tracks4 ,while the average hourly velocity of cyclones is accurately known for the year and for each month1 the movements of individual storms are often very capricious4 ,they may move with a fairly uniform velocity throughout the time of their duration2 they may suddenly and unexpectedly increase their rate of movement1 or they may as suddenly come nearly to a standstill4 ,the characteristics of cyclones vary in different portions of the country and at different times4 ,cyclones which have been accompanied by little precipitation on most of their journey are apt to give increased rain or snowfall as they near the ,atlantic ,ocean and ,gulf of ,st4 ,lawrence4 ,cyclones which over one portion of the country were rainy1 may give little or no precipitation in another portion4 ,cyclones and anticyclones are found to have considerable influence on one another1 retarding or accelerating one another's advance1 or changing one another's normal path of progression4 ,while this mutual interaction is clearly seen1 and may be successfully predicted in many cases1 many other cases arise in which1 under apparently similar conditions1 the result is very different from the anticipation4 ,such are some of the difficulties with which weather forecasters have to contend1 and which prevent the attainment of greater accuracy in weather prediction4 ,,part ,v4----,,problems ,,in ,,observational ,,meteorology4 ,,chapter ,,xx4 ,,temperature4 ,the chief interest and value of the instrumental work in meteorology are to be found not only in the taking of the daily observations at stated hours1 but in the working out of numerous simple problems1 such as may readily be undertaken with the help of the instruments already described4 ,thus1 the temperature of the air 7obtained by the sling thermometer1 supplemented by maximum and minimum thermometers1 and by the thermograph if available7 can be determined under a variety of conditions1 e4g41 close to the ground1 and at different heights above the ground2 at different hours1 by day and night2 in different seasons2 in sunshine and in shade2 during wind and calms2 in clear and cloudy weather2 in woods and in the open2 over bare ground1 grass1 snow1 or ice2 on hills and in valleys4 ,observations may also be made of the temperature of the ground and of a snow cover1 at the surface and at slight depths beneath the surface1 in different seasons and under different weather conditions4 ,among the problems which may be worked out by means of such observations as these are the following3---- ,a4 ,the ,diurnal ,range of ,temperature under ,different ,conditions and at ,different ,heights above the ,ground4----,under the influence of the sun the regular normal variation of temperature during #bd hours is as follows3 ,a gradual increase1 with the increasing altitude of the sun1 from sunrise until shortly after noon1 and a gradual decrease1 with decreasing altitude of the sun1 from the maximum1 shortly after noon1 until the minimum1 about sunrise4 ,this variation is known as the diurnal variation of temperature4 ,curve a in ,fig4 #ab illustrates well the normal diurnal variation of temperature1 as recorded by the thermograph during a period of clear1 warm spring weather 7,april #bg-cj1 #ahhi1 ,nashua1 ,n4 ,h474 ,the diurnal range of temperature is the difference between the maximum and minimum of the diurnal oscillation4 ,the regular normal diurnal variation in temperature is often much interfered with by other controlling causes than the sun1 e4g41 cyclonic winds1 clouds1 etc4 ,i4 ,study and compare the diurnal ranges of temperature as indicated by the maximum and minimum thermometers1 or the thermograph1 in the instrument shelter1 in clear1 fair1 cloudy1 and stormy weather1 during winds and in calms1 in different months4 ,summarize your results by grouping them according to the general weather conditions1 and according to the months or seasons in which the observations were made4 ,for example1 group together and average the ranges observed on clear1 calm days in winter2 on similar days in early summer or autumn2 on clear days with brisk northwest winds in winter2 on similar days in early summer or autumn2 on calm days with overcast sky in the different seasons2 on stormy days with strong winds1 etc4 ,study carefully the weather maps for the days on which your observations are made4 ,pay special attention to the relation between the diurnal ranges and the control exercised over these ranges by cyclones and anticyclones through their winds and general weather conditions4 ,,ii4 ,observations of diurnal ranges of temperature at different heights above the ground may be made by means of maximum and minimum thermometers fastened 7temporarily7 outside of the windows of different stories of the school or of some other building4 ,these observations should be made out of windows facing north1 and care should be taken to check1 so far as possible1 any draft from within the building out through the window during the taking of the observation4 ,if a fire escape is provided on the building1 the instruments may often be conveniently fastened to that4 ,study the ranges under different conditions of wind and weather at various heights above the ground1 and compare these results with those obtained under ,i4 ,notice the relations of all your results to the cyclonic and anticyclonic areas of the weather maps4 ,the diurnal range of temperature in the air over the open ocean from the equator to latitude #dj has been found to average only #b to #c4 ,in southeastern ,california and the adjacent portion of ,arizona the average diurnal temperature range in summer is #dj or #de4 ,over other arid regions1 such as the ,sahara1 ,arabia1 and the interior of ,australia1 the range also often amounts to #dj4 ,observations of temperature above the earth's surface1 in the free air1 made on mountains1 in balloons1 and by means of instruments elevated by kites1 indicate very clearly that the diurnal range of temperature decreases with increasing elevation above sea level4 ,the results obtained at ,blue ,hill ,observatory1 ,massachusetts1 by means of kites1 show that the diurnal range of temperature almost disappears1 on the average1 at #ccjj feet 7#ajjj meters74 ,b4 ,changes of ,temperature in the ,lower ,air1 and their ,control by the ,condition of the ,ground1 the ,movement of the ,air1 and ,other ,factors4----,determine the changes of the temperature in the lower air by making frequent readings of the ordinary thermometer in the instrument shelter1 of the sling thermometer1 or by an examination of the thermograph record4 ,group these changes1 as in ,problem ,a1 so far as possible according to the weather conditions under which they occurred1 and try to classify the kinds of change roughly into types4 ,study the control of these various types by the wind and other weather conditions accompanying them1 as illustrated on the daily weather maps4 ,the control exercised by different conditions of the earth's surface may be studied by means of observations made with the sling thermometer over different surfaces1 such as grass1 bare ground1 snow1 etc4 ,examples of temperature changes in the lower air1 under different conditions of weather1 recorded on the thermograph1 are given in ,fig4 #ab1 and are briefly referred to their causes in the text accompanying that figure4 ,c4 ,vertical ,distribution of ,temperature in the ,atmosphere4----,the vertical distribution of temperature in the lower air may be studied by having ordinary thermometers or thermographs exposed at different heights above the ground1 e4g41 close to the surface2 in an instrument shelter2 out of windows on successive stories of some high building2 and on the roof of the building4 ,they may also1 in cases where there is a hill in the neighborhood1 be exposed in a valley at the bottom of the hill and at successive elevations up the side of the hill4 ,it is1 however1 usually much simpler1 as well as more practicable1 to take these temperature readings by means of the sling thermometer4 ,in the case of observations made out of the windows of a building1 one observer can take the readings at different elevations in succession4 ,when the observations are made at different altitudes on the side of a hill1 it is best to have the coperation of several observers1 who shall all read their thermometers at the same moment of time4 ,the results obtained in the previous problems 7,a and ,b7 may1 of course1 also be utilized in studying the vertical distribution of temperature in the atmosphere4 ,study the vertical distribution of temperature in the lower air under various conditions of weather and season2 at various hours of the day1 and with varying conditions of surface cover4 ,make your observations systematically1 at regular hours1 so that the results may be comparable4 ,group together observations made under similar conditions of weather1 season1 time1 and surface cover4 ,determine the average vertical distribution of temperature in the different cases4 ,note especially any seeming peculiarities or irregularities in this distribution at certain times4 ,study carefully1 as in the previous problems1 the relation of the different types of temperature distribution in the atmosphere to the weather conditions as shown on the daily weather maps4 ,observations made in different parts of the world1 on mountains and in balloons1 have shown that on the average the temperature decreases from the earth's surface upwards at the rate of about #a in #cjj feet of ascent4 ,the rate of vertical decrease of temperature is known in meteorology as the vertical temperature gradient4 ,when it happens that there is for a time an increase in temperature upwards from the earth's surface1 the condition is known as an inversion of temperature4 ,as a result of the decrease of temperature with increasing altitude above sea level1 the tops of many high mountains even in the ,torrid ,zone are always covered with snow1 while no snow can ever fall at their bases1 owing to the high temperatures which prevail there4 ,balloons sent up without aronauts1 but with self-recording instruments1 have given us temperatures of -#ij at a height of #aj miles above the earth's surface4 ,on ,dec4 #d1 #ahif1 ,berson reached a height of #cj1jjj feet and noted a temperature of -#eb4 ,inversions of temperature are quite common1 especially during the clear cold spells of winter4 ,under such conditions the tops and sides of hills and mountains are often much warmer than the valley bottoms at their bases4 ,a good example of an inversion of temperature occurred in ,new ,hampshire on ,dec4 #bg1 #ahhd4 ,the pressure was above the normal1 the sky clear and the wind light4 ,the observer on the summit of ,mt4 ,washington reported a temperature of #af on the morning of that day1 while the thermometers on the neighboring lowlands gave readings of from -#aj to -#bd4 ,in ,switzerland1 the villages and cottages are generally built on the mountain sides and not down in the valley bottoms1 experience having taught the natives that the greatest cold is found at the lower levels4 ,,chapter ,,xxi4 ,,winds4 ,the determination of the direction of the wind 7by means of the wind vane7 and of its velocity 7by means of the anemometer1 or by estimating its strength7 at different hours1 under different conditions of weather and in different seasons1 leads to a number of problems4 ,the following simple investigations may readily be undertaken in schools3---- ,a4 ,the ,diurnal ,variation in ,wind ,velocity in ,fair ,weather4----,observe and record the velocity of the wind 7either estimated or registered by the anemometer7 every hour1 or as often as possible1 on clear or fair days in different months4 ,can you discover any regular change in the velocities during the day8 ,if so1 what is the change8 ,does the season seem to have any control over the results obtained8 ,examine the daily weather maps in connection with your observations and determine the effect that different weather conditions have upon the diurnal variation in wind velocity4 ,the diurnal variation in wind velocity over the open ocean is so slight as hardly to be noticeable4 ,over the land1 the daytime winds are commonly strongest in arid regions4 ,traveling across the desert often becomes extremely disagreeable1 owing to the clouds of dust which these winds sweep up from the surface4 ,b4 ,the ,variations in ,direction and ,velocity due to ,cyclones and ,anticyclones4----,record the direction and velocity of the wind at your station at frequent intervals during the passage of a considerable number of cyclones and anticyclones4 ,enter your observations in some form of table so that they may be readily examined4 7,see p4 #aac47 ,note the character of the changes that occur1 classifying them into types1 so far as possible4 ,study the control of wind directions and velocities by the special features of the individual cyclones and anticyclones as shown on the daily weather maps4 ,how are the different types of change in direction and velocity affected by the tracks of cyclones and anticyclones8 ,by their velocity of progression8 ,by the arrangement of isobars around them8 ,by the height of the barometer at the center8 ,by the season in which the cyclones and anticyclones occur8 ,frequent changes in the direction and velocity of our winds are one great characteristic of the ,temperate ,zones1 especially in winter4 ,the continuous procession of cyclones and anticyclones across the ,united ,states involves continuous shifts of wind4 ,over much of the earth's surface1 however1 the regularity and constancy of the winds are the distinguishing feature of the climate4 ,over a considerable part of the belts blown over by the northeast and southeast trades1 roughly between latitude #cj ,n4 and ,s4 and the equator1 the winds keep very nearly the same direction and the same velocity day after day and month after month4 ,thus the trades are of great benefit to commerce4 ,sailing ships may travel for days in the trade wind belts without having their sails shifted at all1 with a fair wind all the time carrying them rapidly on to their destination4 ,c4 ,the ,occurrence and ,characteristics of ,local ,winds1 such as ,mountain and ,valley and ,land and ,sea ,breezes4----,if the observer happens to be living in or near the mouth of a valley or on a mountain side1 opportunity may be given for the observation of the local winds down the mountain sides and down the valley at night1 and up the valley and the mountain sides by day1 known as mountain and valley breezes4 ,keep a record of wind direction and velocity during the day1 and especially during the morning and evening hours4 ,notice any marked changes in direction1 and the relation of these changes to the time of day4 ,does the velocity of the daytime up-cast breeze show any systematic variation during the day8 ,study the relation of mountain and valley breezes to the general weather conditions shown on the weather maps4 ,how are these breezes affected by season8 ,by the presence of a cyclone over the region8 ,of an anticyclone8 ,by the state of the sky8 ,if near the seacoast 7i4e41 within #aj or #ae miles71 an interesting study may be made of local land and sea breezes4 ,the sea breeze is a wind from the ocean onshore1 while the land breeze blows offshore4 ,these breezes occur only in the warmer months4 ,take frequent observations during the day1 as in the case of mountain and valley winds1 noting especially any changes in direction and velocity1 and the relation of these changes to the time of day4 ,study also the control exercised by the prevailing weather conditions over the occurrence and the strength of development of the land and sea breezes4 ,this problem may be considerably extended by adding temperature observations to the simpler record of wind direction and velocity4 ,in some of the ,swiss valleys the mountain and valley breezes are such regular daily weather phenomena that it has become a weather proverb that a failure of the daily change in wind direction indicates a change of weather4 ,special names are often given to these breezes where they are well marked4 ,in a part of the ,tyrol sailing boats go up the lakes by day with the valley breeze1 and sail back at night with the mountain breeze4 ,it is therefore unnecessary for the boats to be rowed either way4 ,land and sea breezes1 although an unimportant climatic feature in these northern latitudes1 are often of the highest importance in the ,torrid ,zone4 ,the fresh pure sea breeze from over the ocean makes it possible for ,europeans to live in many tropical climates where otherwise they would not keep their health4 ,the land breeze1 on the other hand1 is apt to be an unhealthy wind in the tropics1 especially when it blows off of swampy land4 ,,chapter ,,xxii4 ,,humidity1 ,,dew1 ,,and ,,frost4 ,the humidity of the air1 as determined by the wet and dry-bulb thermometers or the sling psychrometer1 and the occurrence or absence of dew or frost1 should be studied together4 ,observations should be made at different hours1 in different kinds of weather1 and in different seasons4 ,from such observations the following problems may be solved3---- ,a4 ,diurnal ,variation of ,relative ,humidity under ,different ,conditions4----,readings of the wet and dry-bulb thermometers in the instrument shelter1 or of the sling psychrometer1 several times during the day1 will furnish data for determining the diurnal variation of relative humidity4 ,classify your observations according to the weather conditions under which they were made1 and by months or seasons4 ,summarize the results of your investigation1 paying special attention to the relation between the diurnal variation of relative humidity and the temperature4 ,the variations of relative humidity are generally the reverse of those of absolute humidity4 ,in the case of the latter the average diurnal variations are small4 ,the fluctuations in the relative humidity during the day on the northwestern coast of ,europe amount to about #g in ,december and #ag in ,august1 while in central ,asia they average about #be in winter and #ej in summer4 ,b4 ,relation of ,relative ,humidity to the ,direction of the ,wind4----,observations by means of the wet and dry-bulb thermometers in the shelter1 or by means of the sling psychrometer1 supplemented by records of wind direction1 will furnish data for the solution of this problem4 ,tabulate your observations according to wind directions and seasons4 ,determine the characteristics of the different winds as to their relative humidities4 ,consider the control of these winds and humidity conditions by cyclones and anticyclones4 ,the warm wave1 or sirocco1 in front of our winter cyclones in the eastern ,united ,states is a damp1 disagreeable1 irritating wind4 ,in summer1 the sirocco is usually dry1 and during the prevalence of such winds we have our hottest spells1 when sunstrokes are not uncommon4 ,in southern ,italy the sirocco has the same position with reference to the controlling cyclone4 ,there the wind is often so dry as seriously to injure vegetation4 ,the cold wave1 on the rear of our winter cyclones1 with its low temperature and dry air1 often comes as a refreshing change after the enervating warmth of the preceding sirocco4 ,our feelings of bodily comfort or discomfort are thus in a large measure dependent upon the humidity and the movement of the air4 ,c4 ,the ,formation of ,dew4----,the formation of dew is to be studied from the following points of view1 viz41 as dependent upon3 a1 the temperature and the humidity of the air2 b1 the exposure and condition of the ground2 c1 the state of the sky2 and d1 the movement of the air4 ,the occurrence of dew on any night1 as well as the amount1 whether large or small1 can readily be ascertained by inspection4 ,observe the conditions of temperature1 humidity1 cloudiness1 and wind direction and velocity1 as in previous exercises4 ,pay special attention to the state of the sky1 the wind movement1 and the vertical distribution of temperature near the ground4 ,under heading b 7exposure and condition of the ground7 make observations of the amounts of dew formed on hilltops1 hillsides1 and in valleys2 on different kinds of surface covering1 as grass1 leaves1 pavements1 etc41 and over different kinds of soil4 ,classify the results in accordance with the conditions under which the observations were made4 ,compare the results and draw your conclusions from this study4 ,practise making predictions of the formation of dew in different places and under different weather conditions4 ,over the greater portion of the earth's surface the amount of dew which is deposited is very small4 ,it has been estimated that in ,great ,britain the total annual amount would measure only an inch and a half in depth2 and in central ,europe the depth is given as hardly one inch4 ,in some parts of the ,torrid ,zone1 on the other hand1 dew is deposited in much larger quantities4 ,according to ,humboldt1 the traveler through some of the ,south ,american forests often finds what seems to be a heavy shower falling under the trees1 while the sky is perfectly clear overhead4 ,in this case dew is formed on the tops of the tree in sufficiently large quantities to give a shower underneath4 ,it is reported that on the ,guinea coast of ,africa the dew sometimes runs off the roofs of the huts like rain4 ,in many dry regions the dew is an important agency in keeping the plants alive4 ,d4 ,the ,formation of ,frost4----,the formation of frost is to be studied in the same way as that suggested in the case of dew1 i4e41 as dependent upon3 a1 the temperature and the humidity of the air2 b1 the exposure and condition of the ground2 c1 the state of the sky2 and d1 the movement of the air4 ,frosts are usually classified as light or heavy4 ,the words killing frost are also used4 ,study the weather and surface conditions which are most favorable to the formation of frost4 ,pay special attention to the relation of frost and inversions of temperature2 to the frequency of frost on open or sheltered surfaces2 on hills or in valleys1 and on the lower and upper branches of trees and shrubs4 ,determine1 as well as you can1 the weather conditions which precede light or heavy frosts1 and make predictions of coming frosts1 when the conditions warrant them4 ,our ,weather ,bureau gives much attention to the prediction of frosts and to the prompt and widespread distribution of frost warnings4 ,growing crops and fruits are often seriously injured by frosts1 and farmers are naturally anxious to have as early warning as possible of their occurrence4 ,various methods of protecting crops and trees against frost are used4 ,the method most commonly employed consists in the building of fires of brush or other inflammable material on the windward side of the field or the orchard when a frost is expected4 ,the smoke from the fire is blown to leeward across the field1 and acts as an artificial cloud1 affording protection to the vegetation underneath4 ,such fires are known as smudges4 ,,chapter ,,xxiii4 ,,clouds ,,and ,,upper ,,air ,,currents4 ,attentive observation of clouds will soon lead to a familiarity with their common type forms4 ,a series of cloud views1#g with accompanying descriptive accounts1 will teach the names of the clouds and give definiteness to the record4 ,the directions of movement of clouds are determined by means of the nephoscope4 ,cloud observations should be made at different hours1 in different weather conditions1 and in different seasons4 ,the following problems are concerned with clouds and upper air currents3---- ,footnote #g3 ,see ,hydrographic ,office ,cloud ,types1 ,appendix ,b4 ,a4 ,the ,typical ,cloud ,forms and their ,changes4----,note carefully the characteristic forms assumed by clouds2 their mode of occurrence1 whether in single clots1 or in groups1 in lines1 or all over the sky2 their changes in form and in mode of occurrence4 ,classify and summarize your results4 ,compare the clouds of the warm months with those of the cold months4 ,observations have shown that clouds have certain definite characteristic forms which are substantially the same in all parts of the world4 ,this fact makes it possible to give names to the different typical forms1 and these names are used by observers the world over4 ,hence cloud observations1 wherever made1 are comparable4 ,the first classification of clouds was proposed by ,luke ,howard1 in #ahjc4 ,the classification at present in use is known as the ,international ,classification1 and was adopted by the ,international ,meteorological ,congress in #ahif4 ,b4 ,the ,prevailing ,direction of ,cloud ,movements4----,the use of the nephoscope is necessary in the accurate determination of cloud movements4 ,study the prevailing directions of movement of the clouds1 by means of frequent observations with the nephoscope1 in different weather conditions4 ,separate the upper and lower clouds in this study4 ,summarize your results according to the weather conditions and the kinds of clouds4 ,c4 ,correlation of ,cloud ,form and ,movement with ,surface ,winds1 with ,cyclones and ,anticyclones1 and with ,weather ,changes4----,the results obtained in the working out of the two preceding problems may be used in the present problem4 ,tabulate your observations of cloud forms with reference to the wind directions which prevailed at the time of making the observations4 ,do the same with the directions of cloud movement4 ,determine the relation between surface winds and cloud types1 and between surface winds and the direction of the upper air currents1 as shown by the movements of the upper clouds4 ,study the control exercised by cyclones and anticyclones over cloud forms and over the direction of the upper air currents4 ,d4 ,the ,use of ,clouds as ,weather ,prognostics4----,attentive observation of the forms and changes of clouds1 and of the accompanying and following weather changes1 will lead to the association of certain clouds with certain coming weather conditions4 ,make your cloud observations carefully1 taking full notes at the time of observation4 ,give special attention to the weather conditions that follow4 ,continue this investigation through as long a period as possible1 until you have gathered a considerable body of fact to serve as a basis1 and then frame a set of simple rules for forecasting fair or stormy weather on the basis of the forms and changes of the clouds4 ,such local observations as these may be employed as a help in making forecasts from the daily weather maps4 ,clouds were used as weather prognostics long before meteorological observations and weather maps were thought of4 ,to-day sailors and farmers still look to the clouds to give them warning of approaching storms4 ,many of our common weather proverbs are based on the use of clouds as weather prognostics4 ,,chapter ,,xxiv4 ,,precipitation4 ,the special study of various problems connected with precipitation involves detailed observations of the amount and rate of precipitation of various kinds1 measured by the rain gauge during storms in different seasons4 ,these observations of precipitation should1 of course1 be supplemented by the usual record of the other weather elements4 ,the following problems are suggested3---- ,a4 ,the relation of precipitation in general to the other weather elements1 and to cyclones and anticyclones4 ,b4 ,the conditions under which special forms of precipitation 7rain1 snow1 sleet1 hail1 frozen rain7 occur4 ,c4 ,the conditions associated with light and heavy1 brief and prolonged1 local and general rainfall4 ,these problems are studied by means of a careful comparison of full weather records with the daily weather maps during a considerable period of time4 ,rain is the most common form of precipitation the world over1 although snow falls over large portions of both hemispheres4 ,in the ,arctic and ,antarctic zones almost all the precipitation1 which is small in amount1 comes in the form of snow4 ,in southern ,europe snow falls at sea level during the winter as far south as #cf north latitude on the average4 ,in eastern ,asia snow occasionally falls as far south as #bc north latitude4 ,the mean annual rainfall varies greatly in different parts of the world4 ,in desert regions it is practically nothing4 ,at ,cherrapunjee1 in ,india1 it reaches #dic inches1 or over #dj feet4 ,a fall of #dj4h inches in a single day occurred at this station on ,june #ad1 #ahgf4 ,in the ,united ,states1 ,upper ,mattole1 ,cal41 had an extraordinary monthly rainfall of #da4fc inches in ,january1 #ahhh4 ,an excessive daily rainfall of #h inches occurred at ,syracuse1 ,n4 ,y41 on ,june #h1 #ahgf4 ,at ,washington1 ,d4 ,c41 #b4cd inches fell in #cg minutes on ,june #bg1 #ahha4 ,a sudden and very heavy fall of rain occurred at ,palmetto1 ,nevada1 in ,august1 #ahij4 ,a rain gauge which was not exposed to the full intensity of the storm caught #h4hj inches of water in one hour4 ,in ,august1 #ahia1 an observer at ,campo1 ,cal41 measured #aa4e inches as the rainfall in one hour from one very heavy downpour1 and from a portion of a second storm4 ,,chapter ,,xxv4 ,,pressure4 ,the variations of atmospheric pressure1 although insensible to non-instrumental observation1 are so intimately connected with atmospheric processes that they deserve careful attention4 ,their observation leads to several problems4 ,a4 ,the ,decrease of ,pressure with ,height1 as between ,valley and ,hill1 or between the ,base and ,top of a ,building4----,make these observations with the mercurial barometer1 if possible4 ,note the air temperatures at the two levels at which the barometer readings are made4 ,determine the heights of hill or building by means of the following rule3 ,multiply by #i the difference in barometrical readings at the two stations1 given in hundredths of an inch1 and the result will be approximately the difference in height between the stations in feet4 ,a more accurate result may be reached by means of the following rule3 ,the difference of level in feet is equal to the difference of the pressures in inches divided by their sum1 and multiplied by the number #ee1gfa1 when the mean of the air temperatures of the two places is #fj4 ,if the mean temperature is above #fj1 the multiplier must be increased by #aag for every degree by which the mean exceeds #fj2 if less than #fj1 the multiplier must be decreased in the same way4 ,for example1 if the lower station has a pressure of #cj4jj inches and a temperature of #fb1 and the upper station has #bi4jj inches and #eh respectively1 the difference of level between the two will be 7#cj4jj - #bi4jj7 _/ 7#cj4jj #bi4jj7 #ee1gfa #ide feet4 ,if the lower values are #cj4ae inches and #fe1 while the upper values are #bh4fg inches and #ei1 then the formula becomes 7#cj4ae - #bh4fg7 _/ 7#cj4ae #bh4fg7 #ee1gfa 7#b #aag7 #adji feet4 ,the determination of heights by means of the barometer depends upon the fact that the rate of decrease of pressure upwards is known4 ,as the weight of a column of air of a given height varies with the temperature of the air1 it is necessary1 in accurate work of this sort1 to know the air temperatures at both the lower and upper stations at the time of observation4 ,from these temperatures the mean temperature of the air column between the two stations may be determined4 ,tables have been published which facilitate the reductions in this work4 ,the heights of mountains are usually determined1 in the first instance1 by means of barometric observations1 carried out by scientific expeditions or by travelers that have been able to reach their summits4 ,more accurate measurements are later made1 when possible1 by means of trigonometrical methods4 ,b4 ,the ,diurnal and ,cyclonic ,variation of ,pressure in ,different ,seasons4----,this problem is satisfactorily solved only by a study of the curves traced by the barograph1 or by plotting1 as a curve1 hourly or half-hourly readings of the mercurial barometer4 ,the diurnal variation of the barometer is the name given to a slight double oscillation of pressure1 with two maxima and two minima occurring during the #bd hours4 ,this oscillation is in some way1 not yet understood1 connected with the diurnal variation in temperature4 ,it is most marked in the tropics and diminishes towards the poles4 ,fig4 #ae illustrates1 in the ,may curve1 the diurnal variation of the barometer at ,cambridge1 ,mass41 during a spell of fair spring weather1 ,may #ah-bb1 #ahhg4 ,the maxima are marked by and the minima by #j4 ,the cyclonic variation of pressure is the name given to those irregular changes in pressure which are caused by the passage of cyclones and anticyclones4 ,the second curve in ,fig4 #ae shows the cyclonic variations in pressure recorded by the barograph at ,cambridge1 ,mass41 during a spell of stormy weather1 ,feb4 #bc-bh1 #ahhg4 ,these curves serve as good illustrations of these two kinds of pressure variations4 ,study your barograph tracings1 or your barometer readings1 as illustrating diurnal or cyclonic variations of pressure4 ,note the character and the amount of the diurnal and cyclonic variations1 and their dependence on seasons4 ,over the greater part of the ,torrid ,zone the diurnal variation of the barometer is remarkably distinct and regular4 ,humboldt first called attention to the fact that in those latitudes the time of day may be told within about #ae minutes if the height of the barometer is known4 ,c4 ,the ,relation of ,local ,pressure ,changes to ,cyclones and ,anticyclones1 and thus to ,weather ,changes4----,make a detailed study of the relation of the local pressure changes at your station1 as shown by the barograph curves1 or by frequent readings of the mercurial or aneroid barometers1 to the passage of cyclones and anticyclones1 and to their accompanying weather changes4 ,classify the simple types of pressure change1 so far as possible1 together with the general weather conditions that usually accompany these types4 ,apply the knowledge of local weather changes thus gained when you make your forecast on the basis of the daily weather maps4 ,,chapter ,,xxvi4 ,,meteorological ,,tables4 ,the tables which follow are those which are now in use by the ,united ,states ,weather ,bureau4 ,they were first published in the ,instructions for ,voluntary ,observers issued in #ahib1 and were reprinted in #ahig4 ,the following instructions will be found of service in the use of the tables3---- ,,table ,i4----,,dew-,,point4 ,the figures in heavy type1 arranged in vertical columns at each side of the page1 are the air temperatures in degrees ,fahrenheit1 as recorded by the dry-bulb thermometer4 ,the figures in heavy type1 running across the page1 denote the differences1 in degrees and tenths of degrees1 between the dry-bulb and wet-bulb readings1 or1 technically1 the depression of the wet-bulb thermometer4 ,the figures in the vertical columns denote the dew-points4 ,make your observation of the wet and dry-bulb thermometers and note the difference between the two readings4 ,find1 in the vertical columns of heavy type1 the temperature corresponding to your dry-bulb reading1 or the nearest temperature to that4 ,then look along the horizontal lines of figures in heavy type for the figure which corresponds exactly1 or most nearly1 with the difference between your wet and dry-bulb readings4 ,look down the vertical column under this latter figure until you reach the horizontal line corresponding to your dry-bulb reading4 ,at this point the figures in the vertical column give the dew-point of the air at the time of your observation4 ,example3 ,air ,temperature 7dry bulb71 #dg2 ,wet ,bulb1 #dd2 ,difference1 #c4 ,on page #adh will be found the table containing both #dg 7dry bulb7 and #c 7depression of the dew-point74 ,in the twenty-eighth line of this table and in the seventh column will be found the dew-point1 viz41 #da4 ,example3 ,air ,temperature1 #fa4e2 ,wet ,bulb1 #ee4e2 ,difference1 #f4 ,in this case #fa4e is not found in the vertical columns of dry-bulb readings1 but #fa and #fb are found4 ,the dew-point1 with a difference between wet and dry-bulb readings of #f1 for an air temperature of #fa1 is #ej2 for an air temperature of #fb1 it is #eb4 ,evidently1 then1 for an air temperature of #fa4e the dew-point will be #ea1 i4e41 halfway between #ej and #eb4 ,this method of determining dew-points at air temperatures or with depressions of the wet-bulb thermometer which are not given exactly in the tables1 is known as interpolation4 ,example3 ,air ,temperature1 #ic2 ,wet ,bulb1 #ij4e2 ,difference1 #b4e4 ,our table gives no dew-points for wet-bulb depressions of #b4e1 with air temperature #ic1 but we find 7on page #aeb7 that for air temperature #ic and depression of wet bulb of #b1 the dew-point is #ia1 while for a wet-bulb depression of #c1 the dew-point is #hi4 ,by the method of interpolation we can readily determine the dew-point in the special case under consideration as #ij1 i4e41 halfway between #hi and #ia4 ,,table ,,ii4----,,relative ,,humidity4 ,the general plan of this table is the same as that of ,table ,i4 ,the figures in the vertical columns are the relative humidities 7in percentages7 corresponding to the different readings of the wet and dry-bulb thermometers4 ,,table ,,iii4----,,reduction ,,of ,,barometer ,,to #cb4 ,the figures in heavy type1 arranged in vertical columns at the left of the page1 refer to the temperature in degrees ,fahrenheit1 as indicated by the attached thermometer4 ,the figures in heavy type1 running across the top of the page1 are the barometer readings in inches and tenths4 ,make a reading of the attached thermometer and of the barometer4 ,find in the vertical column the temperature corresponding to the reading of the attached thermometer1 and in the horizontal line of heavy figures the reading corresponding to the height of the barometer4 ,the decimal in the vertical column1 under the appropriate barometer reading1 and in the same horizontal line with the appropriate thermometer reading1 is to be subtracted from the height of the barometer as observed1 thus correcting the reading to freezing4 ,when the attached thermometer reads below #bh1 the correction is additive4 ,example3 ,attached ,thermometer1 #fi2 ,barometer1 #cj4jj inches2 ,correction1 -4#aaj2 ,corrected reading1 #bi4hij inches4 ,example3 ,attached ,thermometer1 #gc2 ,barometer1 #bi4ge inches2 ,correction 8 ,we do not find any column corresponding to a barometer reading of #bi4ge inches4 ,we do find1 however1 that with a barometer reading of #bi4ej1 and an attached thermometer reading of #gc1 the correction is -4#aah inch1 and with a barometer reading of #cj4jj1 the correction is -4#abj4 ,by interpolating1 as in the case of the humidity table above1 we find the correction for a barometer reading of #bi4ge inches1 and an attached thermometer reading of #gc4 ,the correction is -4#aai1 and the corrected reading is #bi4ge - 4#aai #bi4fc inches4 ,,table ,,iv4----,,reduction ,,of ,,barometer ,,to ,,sea ,,level4 ,the figures in heavy type1 in the left-hand vertical columns1 are the heights1 in feet1 of the barometer above sea level4 ,the figures in heavy type at the top of the columns1 running across the page1 are the readings of the ordinary thermometer4 ,the numbers of inches and hundredths of inches to be subtracted from the barometer reading 7corrected for temperature by ,table ,,iii71 for the different heights above sea level1 are given in the vertical columns4 ,the altitude above sea level of the city or town at which the observation is made should be ascertained as accurately as possible from some recognized authority1 as1 e4g41 from a railroad survey2 from ,government measurements1 or from some engineer's office4 ,the correction to be made is determined by a simple inspection of the table or by the method of interpolation4 ,example3 ,altitude of ,barometer above sea level1 #hdj feet2 ,temperature of the air1 #dj2 ,correction1 4#ica inch4 ,example3 ,altitude of ,barometer above sea level1 #bje feet2 ,temperature of the air1 #de2 ,correction 8 ,here #bje feet and #de are neither of them found in the table4 ,hence a double interpolation is necessary4 ,for #bjj feet and #dj the correction is 4#bbd inch4 ,for #bjj feet and #ej the correction is 4#bbj inch4 ,hence for #bjj feet and #de the correction is 4#bbb inch4 ,for #baj feet and #dj the correction is 4#bce inch4 ,for #baj feet and #ej the correction is 4#bca inch4 ,hence for #baj feet and #de the correction is 4#bcc inch4 ,now for #bje feet we should have a correction midway between 4#bce inch and 4#bcc inch or 4#bcd inch4 ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t7 t 7,dry ---------------------------------------- ------------7,dry ther47#j4bj4dj4fj4ha4ja4ba4da4fa4hb4jb4b b4db4fther47 ---------------------------------------- ------------------------ -#dj -#eb -#dj -#ci -#ej -#ci -#ch 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---------------------------------------- ---------------------- t4 #b4f #b4h #c4j #c4b #c4d #c4f #c4h #d4j #d4b #d4d t4 t4 #d4f #d4h #e4j #e4b #e4d #e4f #e4h #f4j #f4b #f4d t4 ---------------------------------------- ---------------------- #h #h #i #i #aj -#eg #aj #aa -#da -#fj #aa #ab -#ca -#da -#ei #ab #ac -#be -#ca -#dj -#eh #ac #ad -#bj -#be -#cj -#ci -#ef #ad #ae -#af -#bj -#bd -#cj -#ch -#ec #ae #af -#ac -#af -#ai -#bc -#bh -#cf -#ej #af #ag -#aj -#ab -#ae -#ah -#bb -#bg -#cd -#dg #ag #ah -#g -#i -#ab -#ad -#ag -#ba -#bf -#cb -#dd #ah #ai -#e -#g -#i -#aa -#ad -#ag -#bj -#be -#cj -#dj #ai #bj -#b -#d -#f -#h -#aj -#ac -#af -#ai -#bc -#bi #bj ---------------------------------------- ---------------------- t4 #d4f #d4h #e4j #e4b #e4d #e4f #e4h #f4j #f4b #f4d t4 ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- --------7,dry 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t4 #ab4jab4eac4jac4ead4jad4eae4jae4eaf4jaf4 eag4jag4eah4j t4 ---------------------------------------- ------------------------------------- ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#ah4jai4jbj4jba4jbb4jbc4jbd4jbe4jb f4jbg4jbh4jbi4jcj4jther47 ---------------------------------------- ------------------------------------- #ee -#h #ee #ef -#b -#ai #ef #eg #b -#aj -#dh #eg #eh #f -#c -#bb #eh #ei #i #a -#ab #ei #fj #ab #e -#e -#be #fj #fa #ae #i #j -#ad #fa #fb #ah #ab #e -#f -#bh #fb #fc #bj #ae #i #j -#ad #fc #fd #bb #ah #ab #d -#f -#cb #fd #fe #bd #bj #ae #i #j -#af #fe #ff #bf #bb #ah #ab #d -#g -#cd #ff #fg #bh #bd #bj #ae #i -#a -#af #fg #fh #cj #bf #bc #ah #ab #d -#g -#cg #fh #fi #cb #bh #be #bj #ae #h #j -#ag #fi #gj #cc #cj #bg #bc #ai #ab #e -#g -#ci #gj #ga #ce #cb #bi #be #ba #af #i #j -#ag #ga #gb #cg #cc #ca #bg #bc #ah #ac #e -#f -#ci #gb #gc #ch #ce #cb #bi #be #ba #af #aj #j -#af #gc #gd #dj #cg #cd #ca #bh #bd #ai #ac #f -#f -#cg #gd #ge #db #ci #cf #cb #cj #bf #bb #af #aj #j -#af #ge #gf #dc #da #ch #cd #cb #bh #bd #bj #ad #f -#f -#cd #gf #gg #de #db #dj #cf #cc #cj #bf #bb #ag #aa #a -#ad #gg #gh #dg #dd #da #ch #ce #cb #bh #bd #bj #ad #g -#d -#cj #gh #gi #dh #df #dc #dj #cg #cd #ca #bg #bc #ah #aa #b -#ac #gi #hj #ej #dg #de #db #ci #cf #cb #bi #be #ba #ae #h -#c #hj ---------------------------------------- ------------------------------------- t #ah4jai4jbj4jba4jbb4jbc4jbd4jbe4jbf4jbg4 jbh4jbi4jcj4j t ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -----------7,dry ther47#a4jb4jc4jd4je4jf4jg4jh4ji4jaj4jaa 4jab4jther47 ---------------------------------------- ----------------------- #hj #gi #gg #gf #gd #gc #gb #gj #fh #fg #fe #fc #fb #hj #ha #hj #gh #gg #ge #gd #gc #ga #gj #fh #ff #fe #fc #ha #hb #ha #gi #gh #gg #ge #gd #gb #ga #fi #fh #ff #fd #hb #hc #hb #hj #gi #gh #gf #ge #gc #gb #gj #fi #fg #fe #hc #hd #hc #ha #hj #gi #gg #gf #gd #gc #ga #gj #fh #fg #hd #he #hd #hb #ha #hj #gh #gg #ge #gd #gb #ga #fi #fh #he #hf #he #hc #hb #ha #gi #gh #gf #ge #gc #gb #ga #fi #hf #hg #hf #hd #hc #hb #hj #gi #gh #gf #gd #gc #gb #gj #hg #hh #hg #he #hd #hc #ha #hj #gi #gg #ge #gd #gc #ga #hh #hi #hh #hf #he #hd #hb #ha #hj #gh #gf #gf #gd #gb #hi #ij #hi #hg #hf #he #hd #hb #ha #gi #gh #gg #ge #gd #ij #ia #ij #hh #hg #hf #he #hc #hb #hj #gi #gh #gf #ge #ia #ib #ia #hi #hh #hg #hf #hd #hc #hb #hj #gi #gg #gf #ib #ic #ib #ia #hi #hh #hg #he #hd #hc #ha #hj #gh #gg #ic #id #ic #ib #ij #hi #hh #hf #he #hd #hb #ha #hj #gh #id #ie #id #ic #ia #ij #hi #hg #hf #he #hc #hb #ha #gi #ie #if #ie #id #ib #ia #ij #hh #hg #hf #hd #hc #hb #hj #if #ig #if #ie #ic #ib #ia #ij #hh #hg #hf #hd #hc #ha #ig #ih #ig #if #id #ic #ib #ia #hi #hh #hg #he #hd #hc #ih #ii #ih #ig #ie #id #ic #ib #ij #hi #hh #hf #he #hd #ii #ajj #ii #ih #if #ie #id #ic #ia #ij #hi #hg #hf #he #ajj #aja #ajj #ii #ig #if #ie #id #ib #ia #ij #hh #hg #hf #aja #ajb #aja #ajj #ih #ig #if #ie #ic #ib #ia #ij #hh #hg #ajb #ajc #ajb #aja #ii #ih #ig #if #id #ic #ib #ia #hi #hh #ajc #ajd #ajc #ajb #ajj #ii #ih #ig #if #id #ic #ib #ij #hi #ajd #aje #ajd #ajc #aja #ajj #ii #ih #ig #ie #id #ic #ia #ij #aje #ajf #aje #ajd #ajb #aja #ajj #ii #ih #if #ie #id #ic #ia #ajf #ajg #ajf #aje #ajc #ajb #aja #ajj #ii #ig #if #ie #id #ib #ajg #ajh #ajg #ajf #ajd #ajc #ajb #aja #ajj #ih #ig #if #ie #ic #ajh #aji #ajh #ajg #aje #ajd #ajc #ajb #aja #ii #ih #ig #if #id #aji #aaj #aji #ajh #ajg #aje #ajd #ajc #ajb #aja #ii #ih #ig #if #aaj ---------------------------------------- ----------------------- t4 #a4jb4jc4jd4je4jf4jg4jh4ji4jaj4jaa4jab4j t4 ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#ab4jac4jad4jae4jaf4jag4jah4jai4jb j4jba4jbb4jbc4jbd4jther47 ---------------------------------------- ------------------------------------- #hj #fb #fj #eh #ef #ed #eb #ej #dg #de #db #ci #cf #cb #hj #ha #fc #fa #ei #eg #ee #ec #ea #di #dg #dd #da #ch #ce #ha #hb #fd #fb #fa #ei #eg #ee #ec #ej #dh #de #dc #dj #cg #hb #hc #fe #fd #fb #fj #eh #ef #ed #eb #ej #dg #dd #db #ci #hc #hd #fg #fe #fc #fa #ei #eg #ee #ec #ea #di #df #dc #da #hd #he #fh #ff #fd #fb #fa #ei #eg #ee #ec #ej #dh #de #db #he #hf #fi #fg #ff #fd #fb #fj #eh #ef #ed #eb #di #dg #dd #hf #hg #gj #fh #fg #fe #fc #fa #ei #eg #ee #ec #ea #dh #df #hg #hh #ga #gj #fh #ff #fd #fc #fa #ei #eg #ee #ec #ej #dh #hh #hi #gb #ga #fi #fg #ff #fd #fb #fj #eh #ef #ed #eb #di #hi #ij #gd #gb #gj #fi #fg #fe #fc #fb #fj #eh #ef #ec #ea #ij #ia #ge #gc #gb #gj #fh #fg #fe #fc #fa #ei #eg #ee #ec #ia #ib #gf #gd #gc #ga #fi #fh #ff #fd #fb #fj #eh #ef #ed #ib #ic #gg #ge #gd #gb #ga #fi #fg #ff #fd #fb #fj #eh #ef #ic #id #gh #gg #ge #gc #gb #gj #fi #fg #fe #fc #fa #ei #eg #id #ie #gi #gh #gf #ge #gc #ga #gj #fh #ff #fd #fc #fa #ei #ie #if #hj #gi #gg #gf #gd #gc #ga #fi #fh #ff #fd #fb #fj #if #ig #ha #hj #gh #gg #ge #gd #gb #ga #fi #fg #fe #fc #fa #ig #ih #hc #ha #hj #gh #gg #ge #gc #gb #gj #fh #fg #fe #fc #ih #ii #hd #hb #ha #gi #gh #gf #ge #gc #ga #gj #fh #ff #fd #ii #ajj #he #hc #hb #hj #gi #gg #gf #gd #gc #ga #fi #fg #ff #ajj #aja #hf #hd #hc #hb #hj #gi #gg #ge #gd #gb #ga #fi #fg #aja #ajb #hg #he #hd #hc #ha #hj #gh #gg #ge #gc #gb #gj #fh #ajb #ajc #hh #hg #he #hd #hb #ha #gi #gh #gf #ge #gc #ga #gj #ajc #ajd #hi #hh #hf #he #hc #hb #ha #gi #gh #gf #gd #gc #ga #ajd #aje #ij #hi #hg #hf #he #hc #hb #hj #gi #gg #gf #gd #gb #aje #ajf #ia #ij #hi #hg #hf #hd #hc #ha #hj #gh #gg #ge #gd #ajf #ajg #ib #ia #ij #hh #hg #he #hd #hc #ha #hj #gh #gf #ge #ajg #ajh #ic #ib #ia #hi #hh #hg #he #hd #hb #ha #gi #gh #gf #ajh #aji #id #ic #ib #ij #hi #hh #hf #he #hc #hb #hj #gi #gg #aji #aaj #if #id #ic #ib #ij #hi #hg #hf #he #hc #hb #hj #gi #aaj ---------------------------------------- ------------------------------------- t4 #ab4jac4jad4jae4jaf4jag4jah4jai4jbj4jba4 jbb4jbc4jbd4j t4 ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#bd4jbe4jbf4jbg4jbh4jbi4jcj4jca4jc b4jcc4jcd4jce4jcf4jther47 ---------------------------------------- ------------------------------------- #hj #cb #bi #be #ba #ae #h -#c -#bg #hj #ha #ce #ca #bh #bd #ah #ab #c -#aa #ha #hb #cg #cc #cj #bf #bb #af #i -#b -#bd #hb #hc #ci #ce #cb #bh #bd #ai #ac #e -#i #hc #hd #da #cg #cd #cj #bg #bb #ag #aj #j -#bj #hd #he #db #ci #cf #cb #bi #be #bj #ad #f -#g -#ed #he #hf #dd #da #ch #ce #ca #bh #bc #ah #aa #a -#ag #hf #hg #df #dc #dj #cg #cc #cj #bf #ba #ae #g -#e -#ch #hg #hh #dh #de #db #ci #ce #cb #bh #bd #ai #ab #c -#ac #hh #hi #di #dg #dd #da #ch #cd #ca #bg #bb #af #i -#b -#bh #hi #ij #ea #dh #df #dc #dj #cf #cb #bi #be #bj #ac #d -#aj #ij #ia #ec #ej #dg #de #db #ch #ce #cb #bh #bc #ah #aj #j #ia #ib #ed #eb #di #df #dd #da #cg #cd #cj #bf #ba #ae #g #ib #ic #ef #ec #ea #dh #df #dc #ci #cf #cb #bi #bd #ai #ab #ic #id #eg #ee #ec #ej #dg #de #db #ch #ce #ca #bg #bb #af #id #ie #ei #ef #ed #eb #di #df #dd #dj #cg #cc #cj #be #bj #ie #if #fj #eh #ef #ec #ea #dh #df #dc #ci #cf #cb #bh #bd #if #ig #fa #ei #eg #ee #ec #ej #dg #de #da #ch #cd #ca #bf #ig #ih #fc #fa #ei #eg #ed #eb #di #dg #dd #dj #cg #cc #bi #ih #ii #fd #fb #fj #eh #ef #ed #ea #dh #df #dc #ci #ce #cb #ii #ajj #ff #fd #fb #fj #eg #ee #ec #ej #dh #de #da #ch #cd #ajj #aja #fg #fe #fc #fa #ei #eg #ed #eb #di #dg #dd #dj #cg #aja #ajb #fh #ff #fe #fc #fa #eh #ef #ed #ea #di #df #dc #ci #ajb #ajc #gj #fh #ff #fd #fb #fj #eh #ee #ec #ej #dh #de #da #ajc #ajd #ga #fi #fg #fe #fc #fa #ei #eg #ee #eb #ej #dg #dd #ajd #aje #gb #gj #fi #fg #fe #fc #fa #ei #ef #ed #eb #di #df #aje #ajf #gd #gb #gj #fh #ff #fd #fb #fj #eh #ef #ec #ea #dh #ajf #ajg #ge #gc #ga #gj #fh #ff #fd #fb #fj #eg #ee #eb #ej #ajg #ajh #gf #gd #gc #ga #fi #fg #fe #fc #fa #ei #eg #ed #eb #ajh #aji #gg #gf #gd #gb #ga #fi #fg #fe #fc #fa #eh #ef #ed #aji #aaj #gi #gg #ge #gd #gb #gj #fh #ff #fd #fb #fj #eh #ee #aaj ---------------------------------------- ------------------------------------- t4 #bd4jbe4jbf4jbg4jbh4jbi4jcj4jca4jcb4jcc4 jcd4jce4jcf4j t4 ,,table ,i4----,,temperature ,,of ,,the ,,dew-,,point1 ,,in ,,degrees ,,fahrenheit4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#cf4jcg4jch4jci4jdj4jda4jdb4jdc4jd d4jde4jdf4jdg4jdh4jther47 ---------------------------------------- ------------------------------------- #hi -#bh #hi #ij -#aj #ij #ia #j -#bb #ia #ib #g -#g -#af #ib #ic #ab #b -#d #ic #id #af #h #d -#cg #id #ie #bj #ac #aj -#ab #ie #if #bd #ae #ae -#a -#be #if #ig #bf #ba #ai #g -#h #ig #ih #bi #be #bc #ab #b -#ah #ih #ii #cb #bh #bf #ag #i -#d -#db #ii #ajj #cd #cj #bi #ba #ad #e -#ab #ajj #aja #cg #cb #cb #bd #ah #aa #j -#be #aja #ajb #ci #ce #cd #bg #bb #af #g -#g #ajb #ajc #da #ch #cd #cj #bf #bj #ac #c -#af #ajc #ajd #dd #dj #cg #cb #bi #bd #ah #aj -#b -#ch #ajd #aje #df #dc #ci #ce #ca #bg #bb #ae #f -#aj #aje #ajf #dh #de #db #ch #cd #cj #be #bj #ab #a -#bb #ajf #ajg #ej #dg #dd #dj #cg #cb #bh #bd #ag #i -#e #ajg #ajh #eb #di #df #dc #ci #ce #ca #bg #ba #ad #e -#ac #ajh #aji #ed #ea #dh #de #db #ch #cd #cj #be #ai #ab #j -#bh #aji #aaj #ee #ec #ej #dg #dd #da #cg #cc #bh #bc #ag #h -#g #aaj ---------------------------------------- ------------------------------------- t4 #cf4jcg4jch4jci4jdj4jda4jdb4jdc4jdd4jde4 jdf4jdg4jdh4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t----t74 t 7,dry ---------------------------------------- ------------ 7,dry ther47#j4bj4dj4fj4ha4ja4ba4da4fa4hb4jb4b b4db4f ther47 ---------------------------------------- ------------------------- -#dj #df -#dj -#ci #di -#ci -#ch #ea -#ch -#cg #ed -#cg -#cf #ef -#cf -#ce #ei -#ce -#cd #fa #bb -#cd -#cc #fc #be -#cc -#cb #fe #cj -#cb -#ca #fg #cd -#ca -#cj #fi #ch -#cj -#bi #ga #db -#bi -#bh #gb #de #ag -#bh -#bg #gd #dh #bb -#bg -#bf #gf #ea #bf -#bf -#be #gg #ec #ca -#be -#bd #gh #ef #cd #ab -#bd -#bc #gi #eh #cg #af -#bc -#bb #hj #fj #dj #bj -#bb -#ba #ha #fb #dd #be -#ba -#bj #hb #fd #dg #bi #aa -#bj -#ai #hc #ff #di #cc #af -#ai -#ah #hd #fh #eb #cf #bj -#ah -#ag #he #gj #ed #ci #bd #i -#ag -#af #hf #ga #eg #dc #bh #ad -#af -#ae #hf #gc #ei #df #cb #ai -#ae -#ad #hg #gd #fa #dh #cf #bc #aj -#ad -#ac #hh #gf #fc #ea #ci #bg #ae -#ac -#ab #hh #gg #fe #ec #db #cj #ai #g -#ab -#aa #hi #gh #fg #ef #de #cd #bc #ab -#aa -#aj #ij #gi #fh #eh #dh #cg #bf #af #e -#aj -#i #ij #hj #gj #fj #ej #dj #cj #bj #aj -#i -#h #ij #ha #ga #fb #eb #dc #cc #bd #ad #e -#h -#g #ia #hb #gc #fc #ed #de #cf #bg #ah #i -#g -#f #ia #hc #gd #fe #ef #dh #ci #ca #bb #ac #e -#f -#e #ib #hc #ge #fg #eh #ej #db #cd #be #ag #i -#e -#d #ib #hd #gf #fh #fj #eb #de #cg #bi #ba #ac #e -#d -#c #ib #he #gg #gj #fb #ee #dg #dj #cb #be #ag #aj -#c -#b #ic #hf #gh #ga #fd #eg #ej #db #ce #bh #ba #ad #g -#b -#a #ic #hf #gi #gb #ff #ei #eb #de #ch #ca #be #ah #aa -#a #j #ic #hg #hj #gd #fg #fa #ed #dh #da #ce #bh #bb #ae #j #a #id #hg #ha #ge #fi #fc #ef #ej #dd #ch #cb #be #ai #a #b #id #hh #hb #gf #gj #fd #eh #eb #df #dj #ce #bi #bc #b #c #id #hh #hc #gg #ga #ff #fj #ed #di #dc #cg #cb #bf #c #d #id #hi #hc #gh #gc #fg #fb #ef #ea #de #dj #cd #bi #d #e #ie #hi #hd #gi #gd #fh #fc #eh #ec #dh #db #cg #cb #e #f #ie #ij #he #hj #ge #gj #fe #fj #ed #ej #dd #ci #cd #f #g #ie #ij #he #hj #gf #ga #ff #fa #ef #ea #dg #db #cg #g #h #ie #ia #hf #ha #gf #gb #fg #fb #eh #ec #di #dd #ci #h #i #if #ia #hf #hb #gg #gc #fh #fd #ei #ee #ea #df #db #i #aj #if #ia #hg #hc #gh #gd #fi #fe #fa #eg #eb #dh #dd #aj #aa #if #ib #hg #hc #gi #ge #ga #ff #fb #eh #ed #ej #df #aa #ab #if #ib #hh #hd #hj #gf #gb #fh #fd #fj #ef #eb #dh #ab #ac #if #ib #hh #hd #ha #gg #gc #fi #fe #fa #eh #ed #ej #ac #ad #if #ic #hi #he #ha #gh #gd #gj #fg #fc #ei #ef #eb #ad #ae #if #ic #hi #hf #hb #gi #ge #ga #fh #fd #fa #eg #ed #ae #af #ig #ic #ij #hf #hc #gi #gf #gc #fi #ff #fb #ei #ef #af #ag #ig #ic #ij #hg #hc #hj #gg #gd #gj #fg #fd #fj #eg #ag #ah #ig #id #ij #hg #hd #ha #gh #gd #ga #fh #fe #fb #ei #ah #ai #ig #id #ia #hh #hd #ha #gh #ge #gb #fi #ff #fc #fj #ai #bj #ig #id #ia #hh #he #hb #gi #gf #gc #gj #fg #fd #fa #bj ---------------------------------------- ------------------------- t4 #j4bj4dj4fj4ha4ja4ba4da4fa4hb4jb4bb4db4f t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- ----------7,dry ther47 #b4f #b4h #c4j #c4b #c4d #c4f #c4h #d4j #d4b #d4dther47 ---------------------------------------- ---------------------- -#b #g -#b -#a #aa #d -#a #j #ae #i #j #a #ai #ac #g #a #b #bc #ag #aa #e #b #c #bf #bj #ae #i #d #c #d #bi #bd #ah #ac #h #b #d #e #cb #bg #bb #af #aa #f #e #f #cd #bi #be #bj #ae #aj #e #f #g #cg #cb #bh #bc #ah #ac #i #d #g #h #ci #ce #cj #bf #ba #ag #ab #h #c #h #i #db #cg #cc #bh #bd #bj #ae #aa #g #b #i #aj #dd #dj #ce #ca #bg #bc #ai #ad #aj #f #aj #aa #df #db #ch #cd #cj #bf #bb #ah #ad #aj #aa #ab #dh #dd #dj #cf #cb #bh #be #ba #ag #ac #ab #ac #ej #df #db #ci #ce #ca #bg #bd #bj #af #ac #ad #eb #dh #de #da #cg #cd #cj #bg #bc #ai #ad #ae #ed #ej #dg #dc #dj #cf #cc #bi #bf #bc #ae #af #ef #eb #di #df #db #ci #cf #cb #bi #be #af #ag #eg #ed #ea #dh #dd #da #ch #ce #ca #bh #ag #ah #ei #ef #ec #di #df #dc #dj #cg #cd #ca #ah #ai #fj #eg #ed #ea #dh #de #db #ci #cf #cc #ai #bj #fa #eh #ef #ec #ej #dg #dd #da #ch #ce #bj ---------------------------------------- ---------------------- t4 #b4f #b4h #c4j #c4b #c4d #c4f #c4h #d4j #d4b #d4d t4 t4 #d4f #d4h #e4j #e4b #e4d #e4f #e4h #f4j #f4b #f4d t4 ---------------------------------------- ---------------------- #h #h #i #i #aj #b #aj #aa #f #b #aa #ab #i #e #b #ab #ac #ac #i #e #b #ac #ad #af #ab #i #e #b #ad #ae #ai #af #ab #i #e #b #ae #af #bb #ai #af #ab #i #f #b #af #ag #be #bb #ai #af #ab #i #f #c #ag #ah #bh #be #bb #ai #af #ac #i #f #c #ah #ai #cj #bg #bd #ba #ai #af #ac #aj #g #d #ai #bj #cc #cj #bg #bd #ba #ai #af #ac #aj #g #bj ---------------------------------------- ---------------------- t4 #d4f #d4h #e4j #e4b #e4d #e4f #e4h #f4j #f4b #f4d t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- --------------------7,dry ther47 #j4e #a4j #a4e #b4j #b4e #c4j #c4e #d4j #d4e #e4j #e4e #f4jther47 ---------------------------------------- -------------------------------- #bj #ib #he #gg #gj #fc #ef #dh #da #cd #bg 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#hj #gg #gd #ga #fh #fe #ef #eg #ig #id #ia #hh #hf #hc #hj #gg #gd #ga #fi #ff #eg #eh #ig #id #ia #hi #hf #hc #hj #gh #ge #gb #fi #fg #eh #ei #ig #id #ib #hi #hf #hc #ha #gh #ge #gb #gj #fg #ei #fj #ig #id #ib #hi #hf #hd #ha #gh #ge #gc #gj #fh #fj #fa #ig #id #ib #hi #hg #hd #ha #gh #gf #gc #ga #fh #fa #fb #ig #ie #ib #hi #hg #hd #ha #gi #gf #gd #ga #fi #fb #fc #ig #ie #ib #hi #hg #hd #hb #gi #gg #gd #gb #fi #fc #fd #ig #ie #ib #ij #hg #he #hb #gi #gg #gd #gb #gj #fd #fe #ig #ie #ib #ij #hg #he #hb #hj #gg #ge #gb #gj #fe #ff #ig #ie #ib #ij #hg #he #hb #hj #gh #ge #gc #ga #ff #fg #ih #ie #ic #ij #hh #he #hc #hj #gh #gf #gc #ga #fg #fh #ih #ie #ic #ij #hh #he #hc #ha #gh #gf #gd #ga #fh #fi #ih #ie #ic #ij #hh #hf #hc #ha #gh #gf #gd #gb #fi #gj #ih #ie #ic #ij #hh #hf #hc #ha #gi #gg #gd #gb #gj #ga #ih #ie #ic #ia #hh #hf #hd #ha #gi #gg #ge #gb #ga #gb #ih #ie #ic #ia #hh #hf #hd #hb #gi #gg #ge #gc #gb #gc #ih #ie #ic #ia #hh #hf #hd #hb #hj #gh #ge #gc #gc #gd #ih #ie #ic #ia #hh #hf #hd #hb #hj #gh #gf #gd #gd #ge #ih #ie #ic #ia #hi #hg #hd #hb #hj #gh #gf #gd #ge #gf #ih #ie #ic #ia #hi #hg #he #hb #hj #gh #gf #gd #gf #gg #ih #ie #ic #ia #hi #hg #he #hc #hj #gh #gf #gd #gg #gh #ih #if #ic #ia #hi #hg #he #hc #ha #gi #gg #ge #gh #gi #ih #if #id #ia #hi #hg #he #hc #ha #gi #gg #ge #gi #hj #ih #if #id #ib #hi #hg #he #hc #ha #gi #gg #ge #hj ---------------------------------------- -------------------------------- t4 #j4e #a4j #a4e #b4j #b4e #c4j #c4e #d4j #d4e #e4j #e4e #f4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -----------------7,dry ther47#f4jf4eg4jg4eh4jh4ei4ji4eaj4jaj4ea a4jaa4eab4jther47 ---------------------------------------- ----------------------------- #ai #aj #ai #bj #ac #f #bj #ba #af #i #b #ba #bb #ai #ab #f #bb #bc #ba #ae #i #b #bc #bd #bd #ag #aa #f #bd #be #bf #bj #ad #h #c #be #bf #bh #bc #ag #aa #f #bf #bg #cj #be 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#ef #ec #ej #dg #dd #dj #ch #cd #ca #bh #be #bb #dg #dh #fj #ef #ec #ea #dh #de #db #ci #cf #cc #cj #bg #bd #dh #di #fj #eg #ed #eb #di #df #dc #dj #cg #cd #ca #bi #bf #di #ej #fa #eh #ee #eb #ej #dg #dd #da #ch #cf #cc #cj #bg #ej #ea #fb #ei #ef #ec #ej #dh #de #db #ci #cg #cd #ca #bh #ea #eb #fc #fj #eg #ed #ea #dh #df #dc #dj #ch #ce #cc #cj #eb #ec #fc #fa #eh #ee #eb #di #dg #dd #db #ci #cf #cd #ca #ec #ed #fd #fa #ei #ef #ec #ej #dh #de #dc #dj #ch #ce #cb #ed #ee #fe #fb #ei #eg #ed #ea #di #df #dc #da #ci #cf #cd #ee #ef #fe #fc #fj #eg #ee #eb #ej #dg #dd #db #dj #cg #ce #ef #eg #ff #fd #fa #eh #ee #ec #ej #dh #de #dc #dj #ch #cf #eg #eh #fg #fd #fa #ei #ef #ec #ea #di #df #dd #db #ci #cg #eh #ei #fg #fe #fb #fj #eg #ed #eb #di #dg #de #dc #dj #ch #ei #fj #fh #fe #fc #fj #eh #ee #ec #ej #dh #df #dd #da #ci #fj #fa #fh #ff #fc #fa #eh #ef #ed #ea #di #dg #dd #db #dj #fa #fb #fi #ff #fd #fa #ei #eg #ed #eb #ej #dg #de #dc #da #fb #fc #fi #fg #fd #fb #fj #eg #ee #ec #ea #dh #df #dd #db #fc #fd #gj #fg #fe #fb #fj #eh #ef #ec #ea #di #dg #de #dc #fd #fe #gj #fh #fe #fc #fa #ei #ef #ed #eb #ej #dh #df #dd #fe #ff #ga #fh #ff #fc #fa #ei #eg #ee #ec #ea #di #dg #de #ff #fg #ga #fi #ff #fd #fb #fj #eh #ee #ec #ea #di #dg #de #fg #fh #ga #fi #fg #fe #fc #fj #eh #ef #ed #eb #ej #dh #df #fh #fi #gb #gj #fg #fe #fc #fa #ei #eg #ee #ec #ea #di #dg #fi #gj #gb #gj #fh #ff #fd #fb #fj #eg #ee #ec #eb #ej #dh #gj #ga #gb #gj #fh #ff #fd #fb #fj #eh #ef #ed #eb #ej #dh #ga #gb #gc #ga #fi #fg #fe #fc #fa #ei #eg #ee #ec #ea #di #gb #gc #gc #ga #fi #fg #fe #fc #fa #ei #eg #ee #ec #eb #ej #gc #gd #gd #gb #gj #fh #ff #fd #fb #fj #eh #ef #ed #eb #ej #gd #ge #gd #gb #gj #fh #ff #fd #fb #fj #eh #ef #ee #ec #ea #ge #gf #gd #gb #gj #fh #ff #fd #fc #fa #ei #eg #ee #ec #eb #gf #gg #gd #gc #ga #fi #fg #fe #fc #fa #ei #eg #ef #ed #eb #gg #gh #ge #gc #ga #fi #fg #fe #fc #fb #fj #eh #ef #ed #ec #gh #gi #ge #gc #ga #gj #fh #ff #fd #fb #fj #eh #eg #ee #ec #gi #hj #ge #gc #gb #gj #fh #ff #fd #fc #fa #ei #eg #ee #ed #hj ---------------------------------------- ----------------------------- t4 #f4jf4eg4jg4eh4jh4ei4ji4eaj4jaj4eaa4jaa4 eabjt4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#ab4jab4eac4jac4ead4jad4eae4jae4ea f4jaf4eag4jag4eah4jther47 ---------------------------------------- ------------------------------------- #dj #h #e #a #dj #da #aj #g #d #da #db #ac #aj #f #c #db #dc #ae #ab #i #e #b #dc #dd #ag #ad #aa #h #e #a #dd #de #ai #af #ac #aj #g #d #a #de #df #ba #ah #ae #ab #i #f #c #df #dg #bb #bj #af #ad #aa #h #e #c #dg #dh #bd #ba #ai #af #ac #aj #g #e #b #dh #di #bf #bc #bj #ag #ae #ab #i #g #d #a #di #ej #bg #bd #bb #ai #af #ad #aa #i #f #d #a #ej #ea #bh #bf #bc #ba #ah #af #ac #aj #h #e #c #ea #eb #cj #bg #bd #bb #bj #ag #ae #ab #aj #g #e #eb #ec #ca #bi #bf #bd #ba #ai #af #ad #ab #i #g #d #b #ec #ed #cb #cj #bh #be #bc #bj #ah #ae #ac #aa #h #f #d #ed #ee #cd #ca #bi #bf #bd #bb #ai #ag #ae #ab #aj #h #f #ee #ef #ce #cc #cj #bh #be #bc #ba #ai #af #ad #ab #aj #h #ef #eg #cf #cd #cb #bi #bg #bd #bb #bj #ah #af #ac #aa #i #eg #eh #cg #ce #cc #cj #bh #bf #bd #ba #ai #ag #ae #ac #aa #eh #ei #ch #cf #cd #ca #bi #bg #be #bc #ba #ah #af #ad #ab #ei #fj #ci #cg #cd #cb #cj #bh #bf #bd #bb #bj #ah #af #ad #fj #fa #dj #ch #ce #cc #cb #bi #bg #be #bc #ba #ai #ag #ae #fa #fb #da #ci #cg #cd #cb #cj #bh #bf #bd #bb #bj #ah #af #fb #fc #db #dj #ch #ce #cc #ca #bi #bh #bf #bd #bb #bj #ah #fc #fd #dc #da #ch #cf #cd #cb #cj #bi #bg #be #bc #ba #ai #fd #fe #dd #db #ci #cg #ce #cc #ca #bi #bh #bf #bd #bb #bj #fe #ff #de #db #dj #ch #cf #cd #cb #cj #bi #bg #be #bc #bb #ff #fg #de #dc #da #ci #cg #ce #cc #cb #cj #bh #bf #be #bc #fg #fh #df #dd #db #dj #ch #cf #cd #cc #ca #bi #bg #bf #bd #fh #fi #dg #de #dc #da #ci #cg #ce #cc #cb #cj #bh #bf #be #fi #gj #dh #df #dd #db #dj #ch #cf #cd #cc #ca #bi #bg #bf #gj #ga #dh #df #de #dc #da #ci #cg #ce #cd #cb #cj #bh #bg #ga #gb #di #dg #de #dc #db #dj #ch #cf #ce #cc #ca #cj #bh #gb #gc #ej #dh #df #dd #db #da #ci #cg #ce #cd #cb #cj #bi #gc #gd #ej #dh #dg #de #dc #da #dj #ch #cf #ce #cc #ca #cj #gd #ge #ea #di #dg #df #dd #db #dj #ci #cg #ce #cd #cb #ca #ge #gf #eb #ej #dh #df #de #dc #da #ci #ch #cf #ce #cc #ca #gf #gg #eb #ej #di #dg #de #dd #db #dj #ci #cg #ce #cd #cb #gg #gh #ec #ea #di #dh #df #dd #dc #da #ci #ch #cf #ce #cc #gh #gi #ec #eb #ej #dh #dg #de #dc #db #dj #ci #cg #cf #cd #gi #hj #ed #eb #ea #di #dg #de #dd #db #da #ci #ch #cf #ce #hj ---------------------------------------- ------------------------------------- t4 #ab4jab4eac4jac4ead4jad4eae4jae4eaf4jaf4 eag4jag4eah4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#ah4jai4jbj4jba4jbb4jbc4jbd4jbe4jb f4jbg4jbh4jbi4jcj4jther47 ---------------------------------------- -------------------------------------- #ee #f #a #ee #ef #h #c #ef #eg #i #e #eg #eh #aa #g #b #eh #ei #ab #h #d #ei #fj #ad #aj #f #b #fj #fa #ae #aa #g #c #fa #fb #af #ac #i #e #a #fb #fc #ah #ad #aj #g #c #fc #fd #ai #ae #ab #h #e #a #fd #fe #bj #ag #ac #aj #f #c #fe #ff #bb #ah #ad #aa #h #d #a #ff #fg #bc #ai #af #ab #i #f #b #fg #fh #bd #bj #ag #ad #aj #g #d #a #fh #fi #be #bb #ah #ae #ab #h #e #b #fi #gj #bf #bc #ai #af #ac #aj #g #d #a #gj #ga #bg #bd #bj #ag #ad #aa #h #e #b #ga #gb #bh #bd #bb #ah #ae #ab #i #f #c #a #gb #gc #bi #be #bb #ai #af #ac #aj #h #e #b #gc #gd #cj #bf #bc #bj #ah #ae #ab #i #f #c #a #gd #ge #ca #bg #bd #ba #ai #af #ac #aj #g #e #b #ge #gf #ca #bh #be #bb #bj #ag #ad #aa #h #f #c #a #gf #gg #cb #bi #bf #bc #bj #ah #ae #ab #aj #g #d #b #gg #gh #cc #cj #bg #bd #ba #ai #af #ac #aa #h #f #c #a #gh #gi #cd #ca #bh #be #bb #ai #ag #ad #ab #i #g #d #b #gi #hj #ce #cb #bi #bf #bc #bj #ah #ae #ac #aj #h #f #c #hj ---------------------------------------- ------------------------------------- t4 #ah4jai4jbj4jba4jbb4jbc4jbd4jbe4jbf4jbg4 jbh4jbi4jcj4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- --------------------7,dry ther47 #a4j #b4j #c4j #d4j #e4j #f4j #g4j #h4j #i4jaj4jaa4jab4jther47 ---------------------------------------- --------------------------------- #hj #if #ib #hg #hc #gi #ge #gb #fh #fd #fa #eg #ed #hj #ha #if #ib #hh #hd #hj #gf #gb #fh #fe #fa #eh #ed #ha #hb #if #ib #hh #hd #hj #gf #gb #fi #fe #fb #eh #ee #hb #hc #if #ib #hh #hd #hj #gf #gc #fi #ff #fb #ei #ee #hc #hd #if #ib #hh #hd #hj #gg #gc #fi #ff #fc #ei #ef #hd #he #if #ib #hh #hd #hj #gg #gc #gj #ff #fc #fj #ef #he #hf #if #ib #hh #hd #ha #gg #gc #gj #fg #fc #fj #eg #hf #hg #if #ib #hh #hd #ha #gg #gd #gj #fg #fd #fj #eg #hg #hh #if #ib #hh #he #ha #gg #gd #ga #fg #fd #fa #eh #hh #hi #if #ib #hh #he #ha #gh #gd #ga #fh #fd #fa #eh #hi #ij #if #ib #hh #he #ha #gh #ge #ga #fh #fe #fb #ei #ij #ia #if #ib #hi #he #hb #gh #ge #ga #fh #fe #fb #ei #ia #ib #if #ib #hi #he #hb #gh #ge #gb #fi #fe #fb #ei #ib #ic #if #ic #hi #he #hb #gh #ge #gb #fi #ff #fc #fj #ic #id #if #ic #hi #hf #hb #gi #ge #gb #fi #ff #fc #fj #id #ie #if #ic #hi #hf #hb #gi #gf #gb #fi #ff #fc #fj #ie #if #if #ic #hi #hf #hb #gi #gf #gc #gj #fg #fd #fa #if #ig #if #ic #hi #hf #hb #gi #gf #gc #gj #fg #fd #fa #ig #ih #if #ic #hi #hf #hc #gi #gf #gc #gj #fg #fd #fa #ih #ii #if #ic #hi #hf #hc #hj #gf #gc #gj #fh #fe #fb #ii #ajj #ig #ic #ij #hf #hc #hj #gg #gd #ga #fh #fe #fb #ajj #aja #ig #ic #ij #hf #hc #hj #gg #gd #ga #fh #fe #fb #aja #ajb #ig #ic #ij #hf #hc #hj #gg #gd #ga #fh #fe #fc #ajb #ajc #ig #ic #ij #hg #hc #hj #gg #gd #ga #fi #ff #fc #ajc #ajd #ig #ic #ij #hg #hc #hj #gg #gd #gb #fi #ff #fc #ajd #aje #ig #ic #ij #hg #hd #ha #gh #ge #gb #fi #ff #fd #aje #ajf #ig #ic #ij #hg #hd #ha #gh #ge #gb #fi #ff #fd #ajf #ajg #ig #ic #ij #hg #hd #ha #gh #ge #gb #fi #fg #fd #ajg #ajh #ig #ic #ij #hg #hd #ha #gh #ge #gb #gj #fg #fd #ajh #aji #ig #ic #ij #hg #hd #ha #gh #ge #gc #gj #fg #fe #aji #aaj #ig #id #ij #hg #hd #ha #gh #gf #gc #gj #fg #fe #aaj ---------------------------------------- -------------------------------- t4 #a4j #b4j #c4j #d4j #e4j #f4j #g4j #h4j #i4jaj4jaa4jab4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#ab4jac4jad4jae4jaf4jag4jah4jai4jb j4jba4jbb4jbc4jbd4jther47 ---------------------------------------- ------------------------------------- #hj #ed #ea #dg #dd #da #ch #ce #cb #bi #bf #bc #bj #ah #hj #ha #ed #ea #dh #dd #da #ch #ce #cc #cj #bg #bd #ba #ai #ha #hb #ee #eb #dh #de #db #ci #cf #cc #ca #bh #be #bb #bj #hb #hc #ee #eb #di #df #dc #dj #cg #cd #ca #bi #bf #bc #ba #hc #hd #ef #ec #di #df #dd #da #ch #ce #cb #bi #bg #bd #bb #hd #he #ef #ec #ej #dg #dd #da #ch #cf #cc #cj #bh #be #bb #he #hf #eg #ed #ea #dh #de #db #ci #cf #cd #ca #bi #bf #bc #hf #hg #eg #ed #ea #dh #de #db #dj #cg #cd #cb #cj #bg #bd #hg #hh #eh #ee #eb #di #df #dc #dj #ch #ce #cb #cj #bg #be #hh #hi #eh #ee #eb #di #df #dd #da #ch #cf #cc #ca #bh #bf #hi #ij #ei #ef #ec #ej #dg #dd #da #ci #cf #cd #cb #bi #bf #ij #ia #ei #ef #ec #ej #dg #de #db #ci #cg #ce #cc #cj #bg #ia #ib #ei #ef #ed #ea #dh #de #dc #dj #cg #ce #cc #cj #bh #ib #ic #fj #eg #ed #ea #dh #df #dc #da #ch #cf #cd #ca #bi #ic #id #fj #eg #ed #eb #di #df #dd #da #ci #cf #cd #ca #bi #id #ie #fj #eh #ee #eb #di #dg #dd #db #ci #cg #ce #cb #cj #ie #if #fa #eh #ee #ec #ej #dg #de #db #dj #cg #cf #cc #cj #if #ig #fa #eh #ef #ec #ej #dh #de #dc #dj #ch #cf #cc #ca #ig #ih #fa #ei #ef #ec #ea #dh #df #dc #da #ch #cg #cd #cb #ih #ii #fb #ei #ef #ed #ea #di #df #dd #da #ci #cg #cd #cb #ii #ajj #fb #ei #eg #ed #ea #di #dg #dd #db #ci #cg #ce #cc #ajj #aja #fb #fj #eg #ed #eb #di #dg #de #db #dj #ch #cf #cc #aja #ajb #fc #fj #eg #ee #eb #ej #dg #de #dc #dj #ch #cf #cd #ajb #ajc #fc #fj #eh #ee #ec #ej #dh #de #dc #da #ci #cg #cd #ajc #ajd #fc #fa #eh #ee #ec #ea #dh #df #dd #da #ci #cg #ce #ajd #aje #fd #fa #eh #ef #ec #ea #di #df #dd #db #dj #ch #ce #aje #ajf #fd #fa #ei #ef #ed #ea #di #dg #dd #db #dj #ch #cf #ajf #ajg #fd #fb #ei #eg #ed #eb #di #dg #de #dc #da #ch #cf #ajg #ajh #fd #fb #ei #eg #ed #eb #ej #dg #de #dc #da #ci #cg #ajh #aji #fe #fb #fj #eg #ee #eb #ej #dh #df #dd #da #ci #cg #aji #aaj #fe #fb #fj #eg #ee #ec #ej #dh #df #dd #db #dj #ch #aaj ---------------------------------------- ------------------------------------- t4 #ab4jac4jad4jae4jaf4jag4jah4jai4jbj4jba4 jbb4jbc4jbd4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- -------------------------7,dry ther47#bd4jbe4jbf4jbg4jbh4jbi4jcj4jca4jc 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#ig #ih #cb #bi #bg #be #bc #ba #ai #ah #af #ad #ab #aj #i #ih #ii #cb #cj #bh #bf #bd #bb #bj #ah #af #ae #ac #aa #aj #ii #ajj #cc #ca #bi #bg #be #bc #ba #ai #ag #ae #ad #ab #aj #ajj #aja #cc #ca #bi #bg #be #bc #ba #bj #ah #af #ad #ac #aa #aja #ajb #cd #cb #cj #bh #bf #bd #bb #bj #ai #ag #ae #ac #ab #ajb #ajc #cd #cb #cj #bh #bf #be #bc #ba #ai #ag #af #ad #ab #ajc #ajd #ce #cc #ca #bi #bg #be #bc #bb #bj #ah #af #ae #ac #ajd #aje #ce #cc #ca #cj #bh #bf #bd #bb #bj #ai #ag #ae #ad #aje #ajf #cf #cd #cb #cj #bh #bf #be #bc #ba #ai #ah #af #ad #ajf #ajg #cf #cd #cb #ca #bi #bg #be #bc #bb #bj #ah #ag #ae #ajg #ajh #cg #ce #cc #ca #bi #bg #bf #bd #bb #ba #ai #ag #af #ajh #aji #cg #ce #cc #cb #cj #bh #bf #be #bc #ba #bj #ah #af #aji #aaj #ch #cf #cd #cb #cj #bh #bg #be #bc #bb #bj #ai #ag #aaj ---------------------------------------- ------------------------------------- t4 #bd4jbe4jbf4jbg4jbh4jbi4jcj4jca4jcb4jcc4 jcd4jce4jcf4j t4 ,,table ,,ii4----,,relative ,,humidity1 ,,per ,,cent4 t ,difference between the dry and wet thermometers 7t-t74 t 7,dry ---------------------------------------- --------------------7,dry ther47#cf4jcg4jch4jci4jdj4jda4jdb4jdc4jd d4jde4jdf4jdh4j,ther47 ---------------------------------------- -------------------------------- #hi #a #hi #ij #b #ij #ia #c #a #ia #ib #c #b #a #ib #ic #d #c #b #ic #id #e #d #c #j #id #ie #f #e #d #a #ie #if #g #e #e #b #a #if #ig #h #f #f #c #a #ig #ih #i #g #g #d #b #a #ih #ii #aj #h #g #e #c #b #j #ii #ajj #aj #i #h #f #d #c #a #ajj #aja #aa #i #i #f #e #c #b #j #aja #ajb #ab #aj #i #g #f #d #c #a #ajb #ajc #ab #aa #i #h #f #e #d #b #a #ajc #ajd #ac #ab #aj #h #g #f #e #c #b #ajd #aje #ad #ab #aa #i #h #f #e #d #b #a #aje #ajf #ad #ac #aa #aj #h #g #f #d #c #b #j #ajf #ajg #ae #ad #ab #aa #i #h #f #e #d #c #a #ajg #ajh #af #ad #ac #aa #aj #i #g #f #e #c #b #ajh #aji #af #ae #ac #ab #aj #i #h #g #e #d #c #aji #aaj #ag #ae #ad #ac #aa #aj #h #g #f #e #c #a #aaj ---------------------------------------- -------------------------------- t4 #cf4jcg4jch4jci4jdj4jda4jdb4jdc4jdd4jde4 jdf4jdh4j t4 ,,table ,,iii4----,,reduction ,,of ,,barometer ,,reading ,,to #cb4 ,inches4 ---------------------------------------- ----------------------------------- ,f #bd4j #bd4e #be4j #be4e #bf4j #bf4e #bg4j #bg4e #bh4j #bh4e #bi4j #bi4e #cj4j #cj4e #ca4j ---------------------------------------- -------------------------------------- #cj-4jjc-4jjc-4jjc-4jjc-4jjc-4jjc-4jjc-4 jjc-4jjc-4jjd-4jjd-4jjd-4jjd-4jjd-4jjd #ca 4#jje 4#jje 4#jje 4#jje 4#jjf 4#jjf 4#jjf 4#jjf 4#jjf 4#jjf 4#jjf 4#jjf 4#jjf 4#jjg 4#jjg #cb 4#jjg 4#jjh 4#jjh 4#jjh 4#jjh 4#jjh 4#jjh 4#jjh 4#jji 4#jji 4#jji 4#jji 4#jji 4#jji 4#jji #cc 4#jaj 4#jaj 4#jaj 4#jaj 4#jaj 4#jaj 4#jaa 4#jaa 4#jaa 4#jaa 4#jab 4#jab 4#jab 4#jab 4#jab #cd 4#jab 4#jab 4#jab 4#jab 4#jac 4#jac 4#jac 4#jac 4#jad 4#jad 4#jad 4#jad 4#jae 4#jae 4#jae #ce 4#jad 4#jad 4#jad 4#jae 4#jae 4#jae 4#jaf 4#jaf 4#jaf 4#jaf 4#jag 4#jag 4#jag 4#jah 4#jah #cf 4#jaf 4#jaf 4#jag 4#jag 4#jag 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a4chga4ceia4ccba4cjfa4bhja4bef #acjja4fcga4eiha4efaa4ebea4diaa4deia4dbh a4ciha4cfia4cdba4cafa4bija4bff #acaja4fdia4faja4egca4ecfa4ejba4dgja4dci a4djha4cgia4ceba4cbfa4cjja4bge #acbja4ffaa4fbba4ehda4edha4eaca4dhaa4ddi a4daia4cija4cfba4ccfa4cjia4bhe #accja4fgda4fcda4eifa4eeia4ebea4diba4dfj a4dbia4djja4cgba4cdfa4caia4bid #acdja4fhfa4fdja4fjha4egaa4ecfa4ejca4dga a4ddja4daja4chba4cefa4cbia4cjd #aceja4fiha4feha4fbja4ehba4edga4eada4dhb a4deja4dbja4cica4cffa4ccia4cac #acfja4gaja4ffia4fcaa4eica4eeha4ebda4dib a4dfaa4dcaa4djca4cgea4cdha4cbc #ahgja4gbba4fhaa4fdca4fjea4efia4ecea4ejc a4dgaa4ddaa4daca4chea4ceha4ccb #achja4gcea4fica4feea4fafa4ehaa4edfa4ead a4dhba4deaa4dbca4ciea4cfha4cdb #acija4gdga4gjea4fffa4fbha4eiba4eega4ebd a4diba4dfba4dcca4djea4cgga4cea #adjja4geia4gaga4fgha4fcia4fjca4efha4ece a4ejca4dgba4ddca4daea4chga4cfa #adaja4ggaa4gbia4fija4feja4fada4egia4edf a4eaca4dhba4deca4dbea4ciga4cgj #adbja4ghca4gdaa4gjaa4ffba4fbea4eija4eef a4ebda4diba4dfca4dcea4djfa4chj #adcja4gifa4geca4gaca4fgca4fcfa4fjaa4efg a4ecda4ejca4dgca4ddda4dafa4chi #addja4hjha4gfea4gbda4fhea4jdga4faba4egg a4edea4eaca4dhca4deda4dbfa4cii #adeja4hbja4ggga4gcfa4fifa4feha4fbca4ehh a4eeea4ebca4dica4dfda4dcfa4djh #adfja4hcba4ghha4gdha4gjga4fgja4fcca4eii a4efea4ecca4ejca4dgda4ddea4dah #adgja4hdda4hjja4geia4gaia4jhaa4fdda4fji a4egfa4edca4eaca4dhda4deea4dbg #adhja4hega4haba4ggaa4gcja4fiba4feea4fbj a4ehfa4eeda4ebca4dica4dfea4dcg #adija4hfia4hbda4ghba4gdba4gjca4fffa4fcj a4eiga4efda4ecca4ejca4dgda4ddf #aejja4hhaa4hcfa4gida4geca4gada4fgga4fda a4fjga4egda4edca4eaca4dhda4def ,,appendix ,a4 ,,suggestions ,,to ,,teachers4 ,it is the object of this book to lead the student to the independent discovery of the most important facts in our ordinary weather conditions1 and of the interrelations of the different weather elements4 ,this practical study having taught something as to the real nature of atmospheric phenomena by actual observation1 rapid and substantial progress may be made in the knowledge of the distribution and of the explanation of similar phenomena in other parts of the world1 as derived through a study of the text-books4 ,by means of this combination of the two kinds of study1 the inductive and the didactic1 the advantages of both may be preserved1 and the slow progress of the first method and the unsound progress of the second may be avoided4 ,this book is not a text-book1 and it therefore does not attempt to give explanations of various phenomena discovered by the class4 ,explanations will1 of course1 be called for by the scholars1 in increasing number as the work progresses1 and the larger relations of the study become apparent4 ,it is best1 if possible1 to leave the more complicated matters 7such as the cause of the deflection of the wind from the gradient1 of cyclones and anticyclones1 etc47 until the subjects can be taken up in detail and fully explained1 for instance in the later years of the high school course4 ,it is not advisable to raise such complicated questions in the grammar school work if they can be avoided4 ,the teacher who has a fairly good knowledge of one comprehensive modern text-book of meteorology1 such as ,davis's ,elementary ,meteorology1 will find himself sufficiently well equipped to answer the questions put by the class4 ,the value of the work outlined in this little book can be much increased if the larger applications of the lessons here learned are strongly emphasized4 ,suggestions along this line have been made in fine print throughout the text1 but the examples given may be further extended to the great advantage of the student4 ,careful attention ought to be given to the formulating and writing out of the generalizations reached by the class1 for in these written summaries the results are preserved in compact form4 ,,chapter ,i4 ,the work outlined in this chapter is adapted to the lower grades in the grammar school4 ,it is assumed that the pupils have already had some preliminary training in the simplest non-instrumental weather observations1 such as can readily be made during the primary school years4 ,for the convenience of teachers who may desire it1 a brief outline of work suited to the primary school grades is here given4 ,it is desirable that even older scholars be given some such training as this before they take up the exercises of ,chapter ,,ii4 ,the central idea in this elementary work is to train the children in intelligent weather observation1 so that they may come to appreciate what our typical weather changes are2 that they may recognize the types as they recur1 and may see how each example differs from1 or accords with1 those that have preceded it4 ,we are all so directly affected by the weather conditions prevailing at any time that even the youngest children are forced1 unconsciously to be sure1 to take some notice of these changes4 ,the work of the teacher is1 therefore1 simply to direct attention to what is already seen4 ,when the children come to school on some snowy winter day1 with a northeast wind1 chilling and damp1 attention may be called to the need of overshoes and overcoats1 to the piling up of the snow in deep drifts at certain places near the school or in the town1 while in other places the ground is left bare2 to the ease with which snowballs may be made1 and to other facts which will very readily suggest themselves4 ,a day or two after such a storm1 when the sun is shining bright in a cloudless sky1 when there is no wind and the air is dry1 cold1 and crisp1 the contrasts between these two weather types should be brought out4 ,instead of snow we now have sunshine3 instead of a damp1 chilling northeaster we now have a calm and the air is dry2 snowballs cannot easily be made in the early morning because the snow is frozen hard and is too dry1 but towards noon1 if the temperature rise high enough1 there may be thawing on the tops or sides of the snowdrifts1 and there the snow becomes soft enough for snowballing4 ,another weather type1 often noted during our winter in the central and eastern ,united ,states1 and strongly contrasted with both of the preceding conditions1 is that which brings us a warm1 damp1 southerly wind1 frequently accompanied by heavy rains4 ,as these damp winds blow over snow-covered surfaces they become foggy and the ground is said to 8smoke02 the heavy rain rapidly melts the snow2 slush and mud make bad walking2 rivers and brooks rise rapidly1 perhaps overflowing their banks2 low-lying places become filled with standing water4 ,these and other features should all be brought out by the teacher1 not by telling the class of them directly1 but by judicious questioning1 and they should be contrasted with the conditions which may immediately follow1 when the storm has cleared off1 and when the low temperatures brought by a cold wave1 with its dry northwest wind1 have resulted in freezing lakes1 rivers1 and brooks1 and when skating and sliding may be indulged in4 ,early summer weather conditions1 with their characteristic warm spells1 cumulus clouds1 thunderstorms1 and 7near the coast7 sea breezes1 furnish another long list of typical changes that should be just as carefully noted and described as the more striking winter characteristics4 ,autumn types add further to the list1 which might be extended almost indefinitely4 ,one whole year of the grammar school course may well be given to the observations suggested in ,chapter ,i1 provided that there is no need of hastening on to the more advanced work4 ,the advantage of extending the course over a whole school year is great1 because such extension gives opportunity for becoming familiar with late summer1 autumn1 winter1 spring1 and early summer weather types1 and this is far better than attempting to crowd all the work into one short season4 ,the interest of a class can easily be kept up throughout a school year by means of a progressive system of observations4 ,it is best to vary the observations from time to time1 and to arrange them so that1 beginning with the more simple1 they shall gradually become more complete and more advanced as the year goes on4 ,thus1 starting with temperature observations alone1 these may be continued for one or two weeks before they are supplemented by records of wind direction and velocity4 ,after some practice in the observation of these two weather elements 7say during one month71 data as to the state of the sky may be added4 ,cloud observations themselves may well be graded during successive weeks1 so that1 beginning with the simplest notes concerning amounts of cloudiness1 the pupils shall gradually advance to the point of observing1 and perhaps even of sketching1 the common cloud forms and their changes4 ,thus an important step will have been taken towards appreciating the need of a standard cloud classification1 which may be given later4 ,the addition of records of precipitation completes the list of simple non-instrumental weather observations1 and these records1 as well as the cloud records1 can easily be graded1 so that1 during successive weeks1 every week's work shall be different from that of every other week4 ,in this progression from the simpler to the more complicated observations lies the secret of making the work attractive4 ,nothing will sooner check interest in the study than the necessity of making exactly the same observations day after day and week after week throughout the year4 ,a graded course of non-instrumental observation1 such as is suggested1 gives a very practical general knowledge of our common weather types and changes1 and of the relations of one weather element to another4 ,the questions asked under the different headings in this chapter are designed to awaken the interest of the scholars1 and to call their attention to the more important points of diurnal1 cyclonic1 and seasonal changes in weather elements4 ,the teacher will readily think of other questions which may be suggested for the consideration of the class4 ,although the non-instrumental records are of little value for future reference1 as compared with the instrumental observations1 they should nevertheless be systematically preserved by the class in their record books4 ,after discussion of the daily observations made by the different scholars1 or by one of their number1 the records may be written upon one of the blackboards reserved for this purpose4 ,at the close of the day1 or the next morning1 the blackboard notes should be entered in a record book kept in the schoolroom4 ,the teacher may guide in the discussion of the observations2 may suggest points overlooked by the scholars2 may draw comparisons between the weather conditions of other weeks and of other days4 ,this talking over of the observations is most important1 as it never fails to bring out much of interest4 ,,chapter ,,ii4 ,this work may usually be begun in the early years of the grammar school course1 as soon as the non-instrumental observations have been satisfactorily completed4 ,the scheme of progressive observations already suggested may be followed to advantage in the instrumental work as well as in the non-instrumental4 ,it is often a good plan to have a different scholar assigned to the task of taking the observations every day1 or it may be more advisable to divide the work1 making one responsible for the temperature observations1 another for the precipitation1 etc4 ,it is well to have the daily instrumental weather records written upon the blackboard in the schoolroom1 as already suggested in the case of the non-instrumental observations4 ,at the end of each day the blackboard data should be entered in a permanent record book by some one of the scholars1 and some ingenuity can be exercised in devising the best scheme for keeping this record4 ,the record book should be carefully preserved in the schoolroom1 where it may be referred to by the scholars of future years when any unusually severe storm1 or a spell of excessively hot or dry weather1 or a remarkable cold wave occurs1 in order that comparison with past occurrences of a similar kind may be made4 ,it is well to have the record book of large size1 and to have each day's record entered across two full pages4 ,on the left-hand page the temperature1 pressure1 rainfall1 wind direction and velocity1 etc41 may be entered1 each observation in its proper column1 the number of columns being increased according to the increasing number of observations4 ,the right-hand page may be left for 8,remarks40 ,these 8,remarks0 should include notes of any meteorological phenomena which did not find a place in the columns reserved for the regular observations1 e4g41 occurrence of hail1 or frozen rain2 damage by lightning1 winds1 or floods2 freezing up of rivers or brooks2 interruption of railroad or street-car traffic by snow1 etc41 and1 in general1 explanatory comments on the weather conditions4 ,instructive lessons may be taught as to the relation of the local weather conditions which prevail in the vicinity of the school1 and those of other portions of the country1 by comments on newspaper despatches concerning gales along the coast or on the lakes1 and resulting damage to shipping2 of snow blockades and stalled trains2 of severe thunderstorms and tornadoes2 of hot waves and sunstrokes1 or of cold waves and the destruction of crops or fruits by the frost4 ,the scholars should be encouraged to bring into the class any comments on such phenomena as may be of interest in the work4 ,such of these newspaper clippings as are of the most value may be pasted in the space reserved for the 8,remarks10 where they may be referred to by succeeding classes2 and in this space also may be pasted at the end of each week the barograph and thermograph sheets1 if these instruments are in use at the school4 ,,chapter ,,iii4 ,these observations may usually be profitably undertaken in the later grammar and in the high school years4 ,the instruments described1 while all desirable1 are by no means all necessary1 and no teacher should postpone the establishment of a course in observational meteorology for the reason that a complete set of first-class instruments cannot be secured at the start4 ,if the school is provided with a psychrometer1 there will be no need of the ordinary thermometer1 because the psychrometer gives the true air temperature4 ,it is well1 however1 to have both stationary wet and dry-bulb thermometers1 in the shelter1 for ordinary school use1 and also a sling psychrometer for use in the meteorological field work which forms an important part of the more advanced instrumental work in meteorology4 ,the sling psychrometer may1 of course1 be used simply as an ordinary sling thermometer4 ,the simple form of mercurial barometer1 without vernier and without attached thermometer1 described in ,chapter ,,ii1 will be found the best barometer for general school use4 ,the standard barometer1 described in this chapter1 is too expensive and too complicated to come into extended use in our schools4 ,full instructions concerning the care1 the reading1 and the corrections of the standard mercurial barometer are published by the ,weather ,bureau1 and to these instructions teachers who have such an instrument are referred4 7,see ,appendix ,b47 ,the form of table given at the end of this chapter is intended merely as a suggestion1 and not as a rigid scheme to be adopted in every school4 ,in using the instruments here described1 practice with the maximum and minimum thermometers 7in addition to the simpler work of ,chapter ,,ii7 may be given before any attempt is made to have the class use the psychrometer4 ,and in using the psychrometer one week may well be given to the determination of the dew-point alone1 before the wet and dry-bulb readings are employed to determine the relative humidity4 ,absolute humidity1 which is not referred to in this chapter1 may1 if the teacher deem it advisable1 be added as another weather element for study4 ,a refinement in the notes on the state of the sky is suggested1 viz41 that cloudiness should be recorded in tenths of the sky covered by clouds4 ,this is an advance over the earlier1 less accurate cloud observations1 and is in line with such a progressive scheme as has been recommended4 ,this book is not intended to present a rigid scheme of observational work in meteorology1 alike for all schools1 but rather to make suggestions for the guidance of teachers in laying out such a course as may fit their own cases4 ,under the heading ,summary of ,observations only a few of the most important climatic elements have been noted4 ,the list may easily be extended by the addition of such data as the following3 ,for temperature1 mean diurnal range2 mean diurnal variability 7the mean of the differences between the successive daily means74 ,for humidity1 monthly mean absolute humidity4 ,for precipitation1 the maximum daily precipitation2 the number of rainy and snowy days in every month1 the number of clear1 fair1 and cloudy days in every month2 the mean frequency of rainfall in every month 7number of rainy days divided by the total number of days72 the number of days with thunderstorms1 etc4 ,it is important that the monthly summaries should be discussed in the class1 and that the scholars should give verbal statements as to the numerical results which they have obtained4 ,in this way the work will have a living interest1 which the mere compilation of summaries does not possess4 ,,chapter ,,iv4 ,the first thing for any teacher to do who intends to establish a course in meteorology is to secure a supply of daily weather maps4 ,arrangements should be made to have them mailed regularly from the nearest map-publishing station of the ,bureau4 ,it is important that the ,saturday morning map1 which is usually not sent to schools1 should be included in the set1 as the break of two days 7,saturday and ,sunday7 in every week seriously interferes with the value of the work that may be done on consecutive maps4 ,the maps should be securely fastened up in the schoolroom or in the hall4 ,it is advisable to keep at least two maps thus on view all the time1 in order that the scholars may be able to study the changes from day to day by comparing the last two or three maps with one another4 ,as soon as they are removed from the wall1 the maps should be carefully filed away for future reference4 ,they may be conveniently kept in stiff brown paper folders1 each month's maps being enclosed in a separate folder1 with the name of the month and the year written on the outside4 ,it is a good plan to keep with the file of maps any newspaper clippings referring to notable meteorological phenomena associated with the conditions shown on the maps4 ,thus1 newspaper accounts of the damage done by a hurricane along the ,atlantic ,coast2 of the blockades caused by a heavy snowstorm in the ,northwest2 of tornadoes in the ,mississippi ,valley2 of hot waves and sunstrokes in our larger cities1 will serve to enliven the study of the maps1 and will also help1 in later references to them1 to recall interesting points that might otherwise escape the memory4 ,it is true that newspapers are prone to exaggerate1 and that they are lamentably inaccurate in their use of meteorological terms2 but nevertheless they may often be profitably used in such general studies as these4 ,besides the complete weather map1 the school will need a supply of blank weather maps1 as used by the ,weather ,bureau4 ,these may usually be secured from the nearest map-publishing station at cost price4 ,in the case of the preparation of illustrations for permanent class use1 as suggested later1 it is advisable to employ the blank maps used as the base of the ,washington daily weather maps1 and to be obtained1 at cost price1 on application to the ,chief of the ,weather ,bureau1 ,washington1 ,d4 ,c4 ,these are larger in size 7#af-a_/b by #bc-c_/d inches7 than the station maps1 and the paper is of a better quality4 ,colored illustrations with these ,washington blank maps as the base furnish an economical1 simple1 and effective means of teaching elementary meteorology4 ,,chapter ,v4 ,in this chapter a series of six consecutive weather maps is taken as the basis of the work4 ,the study of the weather elements on such a series of maps gives a far clearer understanding of the distribution of these elements and of their relation one with another1 than if a far larger number of single maps are studied which do not follow one another in regular sequence4 ,teachers should add to the map-drawing exercises by giving their classes the data from other sets of maps selected from the school files4 ,summer maps as well as winter ones should be used1 in order that too much emphasis may not be laid on winter conditions4 ,the search for the various cities in which ,weather ,bureau stations are established1 involved in the work of entering the data on the blank maps1 furnishes excellent practice in geography4 ,this exercise may be varied1 and practice in the location of the different ,states may be given1 if the teacher reads out to the class the temperatures in different parts of the various ,states1 as1 e4g41 central ,arizona1 #cd2 southwestern ,tennessee1 #cj2 northern ,nevada1 #ch1 etc4 ,as the ,state names are not given on the ,weather ,bureau maps1 such a method as this will give a very desirable familiarity with the relative positions of the ,states of the ,union4 ,if the school possesses a blackboard outline map of the ,united ,states1 it may be a good plan1 if the class is small1 to have one of the pupils enter the temperatures and draw the isotherms on the board before the class1 and to let the others correct him if they see that he is going wrong4 ,as to irregularities in the isotherms1 which may cause trouble1 the officials of the ,weather ,bureau vary somewhat among themselves in dealing with such cases1 and no definite rules can be laid down to fit all occasions4 ,it is best to select maps with few irregularities at first1 and in time experience will show how the exceptional cases may be treated4 ,by the scheme of coloring isothermal maps1 suggested in this chapter1 a valuable series of permanent illustrations of noteworthy weather types for class use can readily be prepared at very slight cost4 ,for the purposes of these colored illustrations it is best to use the large scale ,washington blank weather maps1 as suggested in the preceding chapter1 and to have each map mounted on heavy cardboard after it has been colored4 ,by means of this mounting the maps are prevented from tearing1 and can be kept smooth and in good condition4 ,the scheme of coloring may be varied to suit the fancy of the scholars1 for the preparation of these permanent illustrations may well be intrusted to those of the class who are especially interested in the work1 and who are skillful in their use of the paint brush4 ,the work is really very simple and needs only ordinary care4 ,as soon as the drawing of isotherms and the coloring of isothermal charts have been sufficiently studied1 the teacher should hang up the daily weather map each day 7or a blank map with the isotherms for the day drawn on it71 and should call attention to the temperature changes from day to day4 ,in this way the facts of actual temperature changes experienced by the class will be associated with the larger temperature changes shown on the weather maps4 ,the sections on temperature gradients may be postponed1 if the teacher deems it advisable1 until other matters of a simpler nature are passed4 ,the idea of rates of change is not an easy one for students to grasp1 and it is far better to postpone the consideration of this subject than to involve the class in any confusion at this stage4 ,it is a mistake1 however1 to omit these sections altogether1 as a clear conception of the principle of rates is a valuable part of a student's mental equipment4 ,it is a good plan1 in the exercises on lines of temperature decrease1 to have maps prepared with faint isotherms and heavy lines of temperature decrease1 in order to emphasize the idea of change of temperature1 in contrast to the idea of constancy of temperature expressed by the isotherms4 ,,chapter ,,vi4 ,in the work on the wind charts it is essential to proceed very slowly1 in order that the best results may be obtained by the pupils4 ,some of the aberrant wind courses1 which complicate the discovery of the cyclonic and anticyclonic spirals1 may well be omitted in the case of the younger classes1 and considerable assistance in facilitating these discoveries may be given by suggestions as to adding intermediate dotted wind arrows1 in sympathy with the observed wind directions4 ,the anticyclonic systems are always much more difficult to discover than the cyclonic1 and care should be taken to assist the class in this matter as much as seems necessary4 ,the questions in the text are merely suggestive1 and are by no means as numerous as it would be well to make them in the class4 ,the discovery of the spirals will probably be made by degrees4 ,the concise formulation of the facts discovered will furnish excellent basis for exercises in writing4 ,it is interesting to note that the discussion as to whether the winds blow circularly around1 or radially in towards1 centers of low pressure1 which usually comes up in every class in meteorology at some stage in the study1 was carried on in a very animated way about the middle of the present century in this country4 ,two noted ,american meteorologists1 ,redfield and ,espy1 and their respective followers1 took opposite sides in this controversy1 ,redfield maintaining at the start that the winds moved in circles1 and ,espy maintaining that they followed radial courses4 ,the truth lay between the two4 ,,chapter ,,vii4 ,the study of atmospheric pressure is not easy1 because the pupils cannot perceive the changes in pressure from day to day by their unaided senses4 ,especially difficult does this study become if the class has not already had some practice in making barometer readings4 ,when this observational work has not preceded the consideration of the isobaric lines of the daily weather maps1 the teacher should introduce the subject of pressure very carefully4 ,the experiment with the ,torricellian tube will show the class something of the reality of atmospheric pressure1 and the variations in this pressure from day to day can readily be made apparent by means of a few barometer readings1 if time cannot be spared for a regular and continued series of barometer observations4 ,a word may be said as to the correction of barometric readings for local influences1 in order to make these readings comparable1 if this matter has not been previously met with1 but care should be taken not to confuse the younger pupils too much with explanations at this stage of the work4 ,it may be well to omit this point unless it is brought up by some pupil4 ,the questions asked in the text are merely suggestive4 ,they may be added to and varied at the discretion of the teacher4 ,lines of pressure-decrease should be drawn on all isobaric charts studied in the class1 as they are highly instructive4 ,when the isobars are near together1 these lines of pressure-decrease may be drawn heavier1 to indicate a steeper gradient4 ,the convergence of these lines towards regions of low pressure1 and their divergence from regions of high pressure1 seen on every map on which these gradients are drawn1 emphasizes an important lesson4 ,before measuring rates of pressure-decrease by means of a scale1 considerable practice should be given in the study1 by means of the eye1 of the rapidity or slowness of decrease of pressure1 as shown by the heavier or lighter lines of pressure-decrease4 ,when the broad facts of differing rates are comprehended1 then the actual measurement of these rates is a comparatively easy matter4 ,in any case1 however1 an appreciation of these rates of change is not always readily gained1 even by older scholars in the high school4 ,it is1 therefore1 of prime importance to proceed very slowly indeed at this point1 and to have every step fully understood before another step is taken4 ,the instructions in the text for measuring rates of pressure-decrease are1 that these rates shall be recorded as so many hundredths of an inch of change of pressure in one latitude-degree4 ,this is done for the sake of simplicity4 ,if this rate is expressed in hundredths of an inch of pressure in a quarter of a latitude-degree of distance1 the numerical value is the same as if expressed in millimeters of pressure per latitude-degree of distance4 ,,chapter ,,viii4 ,the fact of the prevalence of different kinds of weather over the country at the same time is of great importance4 ,it should be strongly emphasized by the teacher in the course of the discussion of the maps of weather distribution4 ,additional exercises of the same sort may be given to advantage1 by letting the class plot and study the weather signs taken from any current weather map4 ,instructive lessons may be taught by talking over1 in the class1 the different ways in which people all over the country are affected by the character of the weather that happens to prevail where they are4 ,,chapters ,,ix-,,xviii4 ,the correlation exercises will1 as a whole1 teach few entirely new facts to the brighter scholars who have faithfully completed the preceding work in observations and in the construction and study of the daily weather maps4 ,these exercises do1 however1 lead to detailed examination and to the careful working out of the relations which may have been previously noticed in a general way only4 ,they give the repeated illustration which is necessary in order to impress firmly on the mind the lesson that the weather map has to teach4 ,it is a good plan to let different scholars work out the problems for different months4 ,the results reached in each case should be discussed in the class1 and thus each member may have the double advantage of working out his own problem1 and of profiting by the work done by his fellows4 ,throughout these exercises care should be taken to have weather maps of all months studied4 ,the exercise on the correlation of the velocity of the wind with the pressure cannot be undertaken unless the work on temperature and pressure gradients 7,chapters ,v and ,,vii7 has been completed4 ,,chapters ,,xx-,,xxv4 ,it is not expected that any one scholar can accomplish all that is here outlined4 ,examples may be selected from the list1 as opportunity offers1 so that each scholar shall become familiar with several problems4 ,few of the problems suggested call for continuous routine observation at fixed hours4 ,they require1 on the other hand1 an intelligent examination of ordinary weather phenomena1 with special reference to discovering their explanation4 ,in most of the problems a small number of observations will suffice4 ,under the supervision of the teacher1 different problems may be assigned to the several members of a class2 or several scholars may work on different parts of the same problem1 exchanging records in order to save time4 ,all the scholars should have a general knowledge of the results which have been obtained from the observations made by the other members of their class4 ,the teacher will use his discretion in arranging the order of the problems1 and in selecting those that are best suited to the season in which the work is done1 to the locality in which the school is situated1 and to the facilities and apparatus at command4 ,although the variety of accessible problems is less in city schools than in country schools1 much may be done in the city as well as in the country4 ,the opportunities for carrying out such observational work vary so much in different schools that it is impossible to give specific instructions1 which shall be available in all cases4 ,some general suggestions are therefore given1 which the teacher may supplement by more detailed instructions framed to fit the particular circumstances of each case4 ,a review of the headings of the different problems shows that a very general correlation exists among them1 whereby the subjects of every heading are associated with those of nearly every other4 ,in other words1 every weather element is treated as a function of several other elements4 ,it follows from this that the variety of work here outlined is more apparent than real1 and that many problems which appear from their wording to be entirely new are in large part rearrangements of problems previously encountered4 ,,appendix ,b4 ,,the ,,equipment ,,of ,a ,,meteorological ,,laboratory4 ,a4 ,,instruments4 ,exposed ,thermometer 7,united ,states ,weather ,bureau pattern71 with brass support1 #b4ge4 ,maximum and ,minimum ,thermometers 7,united ,states ,weather ,bureau pattern71 mounted together on one board1 #f4be4 ,wet- and ,dry-,bulb ,thermometers 7,united ,states ,weather ,bureau pattern71 mounted on one board1 complete with water cup1 #f4ej4 ,sling ,psychrometer 7designed by ,professor ,c4 ,f4 ,marvin1 of the ,united ,states ,weather ,bureau71 consisting of two exposed mercurial thermometers1 mounted on an aluminum back1 and provided with polished1 turned hard-wood handle and brass trimmings1 #e4jj4 ,sling ,psychrometer1 consisting of two cylindrical bulb thermometers1 mounted one a little above the other upon a light brass frame1 with a perforated guard to protect the bulbs while swinging1 but which can be raised 7by sliding upon the frame7 for the purpose of moistening the linen covering of the wet bulb4 ,much less liable to be broken than the ,weather ,bureau pattern1 #e4jj4 ,rain ,gauge 7,united ,states ,weather ,bureau standard71 #h inches in diameter1 complete1 with measuring stick1 #e4be4 ,rain ,gauge1 #c inches in diameter1 with overflow and measuring stick1 #a4be4 ,wind ,vane 7,united ,states ,weather ,bureau pattern71 #aj4jj4 ,anemometer 7,united ,states ,weather ,bureau pattern71 with indicator1 aluminum cups1 and electrical attachment1 #be4jj4 ,the same1 with painted brass cups1 #bc4jj4 ,anemometer ,register 7,united ,states ,weather ,bureau pattern71 with pen and ink attachment1 #ce4jj4 ,the same1 with pencil attachment 7old style71 #bd4jj4 ,aneroid ,barometer 7for meteorological work71 #ad4jj-af4jj4 ,,note4----,much cheaper aneroids can be purchased1 and may be used to some advantage in the simpler observations in schools4 ,mercurial ,barometer 7,standard ,united ,states ,weather ,bureau pattern71 complete with attached thermometer1 vernier1 etc41 #cj4jj-cc4jj4 ,,note4----,the above instruments1 as used by the ,united ,states ,weather ,bureau1 are made by ,h4 ,j4 ,green1 #aaia ,bedford ,avenue1 ,brooklyn1 ,n4 ,y4 ,the prices are those given in ,green's latest catalogue4 ,mercurial ,barometer4 ,new improved form1 especially designed for school use4 ,mounted on mahogany back4 ,scale engraved on aluminum4 ,divisions of scale on metric and ,english systems4 ,no vernier1 #e4ge4 7,l4 ,e4 ,knott ,apparatus ,co41 #ad ,ashburton ,place1 ,boston1 ,mass47 ,thermograph 7designed by ,dr4 ,daniel ,draper1 of ,new ,york74 ,consists of a bimetallic thermometer in a case which carries a disk1 with a chart upon its axle instead of hands like the ordinary clock4 ,a pen 7resting on the face of the disk7 registers the fluctuations of temperature as the chart is carried around4 ,sizes1 #ad #bj inches1 #cj4jj2 #aj #ad inches1 #ae4jj4 ,this instrument may be purchased of ,h4 ,j4 ,green4 ,thermograph4 ,self-recording thermometer 7as adopted by the ,united ,states ,weather ,bureau71 made by ,richard ,frres1 of ,paris4 ,records continuously on a sheet of paper wound around a revolving drum1 which is driven by clock-work inside4 ,standard size 7without duty71 #cj4jj4 ,barograph4 ,self-recording barometer 7as adopted by the ,united ,states ,weather ,bureau71 made by ,richard ,frres1 of ,paris4 ,similar in general arrangement to the thermograph4 ,standard size 7without duty71 #bg4fj4 ,these last two instruments can be procured through ,glaenzer ,frres ,rheinboldt1 #bf #bh ,washington ,place1 ,new ,york ,city4 ,instrument ,shelter 7standard ,united ,states ,weather ,bureau pattern7 will hold a set of maximum and minimum thermometers1 psychrometer1 and a thermograph4 ,may be set up on top of posts driven into the ground1 or may be attached to a wall1 #ah4jj4 ,barometer ,box1 for the standard mercurial barometer4 ,made of mahogany1 with glass panels on front and sides2 lock and key1 and with fittings complete1 #h4ej4 ,these may be purchased of ,h4 ,j4 ,green4 ,b4 ,,text-,,books4 ,the ,story of the ,earth's ,atmosphere4 ,,douglas ,,archibald4 ,new ,york1 ,d4 ,appleton ,co41 #ahih4 #ahmo1 pp4 #aid4 #dj cents4 ,to be recommended to the general reader who wishes to gain some knowledge of meteorology quickly4 ,not a text-book4 ,contains a chapter on 8,flight in the ,atmosphere40 ,elementary ,meteorology4 ,,william ,,morris ,,davis4 ,boston1 ,ginn ,co41 #ahih4 #hvo1 pp4 #cee4 #b4ej4 ,the most complete of the modern text-books1 and the best adapted for use in the systematic teaching of meteorology4 ,the modern views are presented clearly and without the use of mathematics4 ,portions of it are somewhat too advanced for school study1 but teachers will find it invaluable as a reference book in directing the laboratory work1 and in answering the questions of school classes4 ,a ,popular ,treatise on the ,winds4 ,,william ,,ferrel4 ,new ,york1 ,john ,wiley ,sons1 #ahij4 #hvo1 pp4 #eje4 #c4dj4 ,this can hardly be regarded as a popular treatise4 ,it embodies1 in condensed and chiefly non-mathematical form1 the results of ,ferrel's researches during his long and profound study of the general circulation and phenomena of the atmosphere4 ,teachers who advance far into meteorology will find this book indispensable4 ,it is not at all suited for general class-room use4 ,american ,weather4 ,a4 ,w4 ,,greely4 ,new ,york1 ,dodd1 ,mead ,co41 #ahhh4 #hvo1 pp4 #bhf4 ,out of print1 but secondhand copies are probably obtainable4 ,deals1 as the title implies1 especially with the weather phenomena of the ,united ,states4 ,contains brief accounts of individual hot and cold waves1 hurricanes1 blizzards and tornadoes1 and gives specific data concerning maxima and minima of temperature1 precipitation1 etc41 in the ,united ,states4 ,meteorology3 ,practical and ,applied4 ,,john ,,william ,,moore4 ,london1 ,f4 ,j4 ,rebman1 #ahid4 #hvo1 pp4 #dde4 #h shillings4 ,a readable book4 ,considerable space is given to instrumental meteorology4 ,contains chapters on the climate of the ,british ,isles and on the relations of weather and disease in the ,british ,isles4 ,especially adapted for the use of ,english readers4 ,elementary ,meteorology4 ,,robert ,h4 ,,scott4 ,international ,scientific ,series4 ,london1 ,kegan ,paul1 ,trench ,co41 #ahhe2 ,boston1 ,a4 ,a4 ,waterman ,co41 #ahhi4 #hvo1 pp4 #daj4 #f shillings4 ,the standard text-book in ,great ,britain4 ,the author is secretary to the ,meteorological ,council of the ,royal ,society4 ,fairly complete1 but now somewhat out of date in some portions4 ,it is a useful book in a meteorological library1 but does not treat the subject in a way very helpful to the teacher4 ,meteorology4 ,,thomas ,,russell4 ,new ,york1 ,the ,macmillan ,company1 #ahie4 #hvo1 pp4 #bgg4 ,brief and incomplete as a text-book of meteorology1 but containing a very comprehensive account1 fully illustrated1 of rivers and floods in the ,united ,states1 and their prediction4 ,elementary ,meteorology4 ,,frank ,,waldo4 ,new ,york1 ,american ,book ,company1 #ahif4 #hvo1 pp4 #cgc4 #ij cents4 ,a compact summary4 ,useful to teachers as a handy reference book4 ,modern ,meteorology4 ,,frank ,,waldo4 ,new ,york1 ,charles ,scribner's ,sons1 #ahic4 #hvo1 pp4 #dfj4 #a4be4 ,very complete account of meteorological apparatus and methods1 and admirable summary of recent ,german studies of the thermodynamics and general motions of the atmosphere4 ,c4 ,,instructions ,,in ,,the ,,use ,,of ,,instruments4 ,instructions for ,voluntary ,observers4 #ahii4 #hvo1 pp4 #bc4 ,brief instructions for taking and recording observations of temperature and precipitation with ordinary and maximum and minimum thermometers and with the rain gauge4 ,barometers and the ,measurement of ,atmospheric ,pressure4 ,c4 ,f4 ,,marvin4 #ahid4 #hvo1 pp4 #gd4 ,a pamphlet of information respecting the theory and construction of barometers in general1 with summary of instructions for the care and use of the standard ,weather ,bureau instruments4 ,instructions for ,obtaining and ,tabulating ,records from ,recording ,instruments4 #ahih4 #hvo1 pp4 #ca4 ,contains directions concerning the care and use of the ,richard thermograph and barograph4 ,,note4----,these pamphlets are prepared under the direction of ,professor ,willis ,l4 ,moore1 ,chief of the ,united ,states ,weather ,bureau1 and are published1 under authority of the ,secretary of ,agriculture1 by the ,weather ,bureau4 ,they will be found the best guides in making observations1 the care of instruments1 etc4 ,d4 ,,journals1 ,,etc4 ,monthly ,weather ,review4 ,prepared under the direction of ,willis ,l4 ,moore1 ,chief of ,weather ,bureau1 ,professor ,cleveland ,abbe1 ,editor4 ,united ,states ,department of ,agriculture1 ,weather ,bureau1 ,washington1 ,d4 ,c4 #aj cents a copy4 ,an invaluable publication for teachers and students alike4 ,contains complete meteorological summaries for each month2 accounts of all notable storms1 cold and hot waves1 etc42 and a large number of articles on a wide range of meteorological subjects4 ,the charts show the tracks of areas of high and low pressure which crossed the ,united ,states during the month1 the total precipitation1 sea-level pressure1 temperature and surface winds1 percentage of sunshine1 etc41 for the month4 ,other charts are also frequently added4 ,the ,journal of ,school ,geography4 ,professor ,richard ,e4 ,dodge1 ,teachers ,college1 ,columbia ,university1 ,new ,york ,city1 ,editor4 ,publication ,office1 #da ,no4 ,queen ,street1 ,lancaster1 ,pa4 ,ten numbers a year4 #a4jj per annum4 ,a monthly journal devoted to the interests of the common school teacher of geography4 ,contains numerous articles and notes on meteorological and climatological subjects4 ,science4 ,edited by ,professor ,j4 ,mc,k4 ,cattell1 ,columbia ,university1 ,new ,york ,city1 ,new ,york1 ,the ,macmillan ,company4 ,weekly4 #e4jj per annum4 ,devoted to the advancement of all sciences4 ,contains brief ,current ,notes on ,meteorology1 which summarize the more important meteorological publications4 ,monthly ,bulletins of the ,climate and ,crop ,service of the ,weather ,bureau4 ,these ,bulletins are issued every month at the central office of the ,weather ,bureau in each ,state1 under the direction of the ,section ,director of the ,climate and ,crop ,service in that ,state4 ,they contain meteorological data for the month1 and frequently notes of interest4 ,the annual summaries are especially valuable4 ,e4 ,,charts4 ,daily ,weather ,maps4 ,these are published at the central office of the ,weather ,bureau in ,washington1 and at eighty-four other stations of the ,bureau throughout the ,united ,states4 ,it is best to have the daily maps sent from the nearest map-publishing station1 and not from ,washington1 as the delay in the latter case is often so great that much of the immediate value of the maps is lost4 ,climate and ,crop ,bulletin of the ,united ,states ,weather ,bureau4 ,washington1 ,d4 ,c4 ,monthly4 ,chart showing1 by means of small maps1 the actual precipitation1 departures from normal precipitation1 departures from normal temperature1 and maximum and minimum temperatures4 ,also a printed summary of the weather and of the crop conditions in the different sections of the ,united ,states4 ,issued on the first of each month4 ,snow and ,ice ,chart of the ,united ,states ,weather ,bureau4 ,washington1 ,d4 ,c4 ,weekly during the winter season4 ,based on data from regular ,weather ,bureau stations1 supplemented by reports from selected voluntary observers4 ,shows1 by shading1 the area covered with snow at #h ,p4,m4 each ,tuesday during the winter1 and by lines1 the depth of snow in inches4 ,explanatory tables and text accompany the chart4 ,storm ,bulletin of the ,united ,states ,weather ,bureau4 ,washington1 ,d4 ,c4 ,issued at irregular intervals4 ,charts1 with text1 illustrating the history of individual notable storms4 ,pilot ,chart of the ,north ,atlantic and ,north ,pacific ,oceans4 ,hydrographic ,office1 ,bureau of ,equipment1 ,department of the ,navy1 ,washington1 ,d4 ,c4 ,monthly4 ,price #aj cents a copy4 ,shows calms and prevailing winds1 ocean currents1 regions of fog and equatorial rains1 the positions of icebergs and wrecks1 steamship and sailing routes1 storm tracks1 magnetic variation1 etc4 ,also gives isobars and isotherms and a forecast for the month succeeding the date of publication1 and a review of the weather over the oceans for the preceding month4 ,supplementary charts are occasionally issued4 ,rainfall and ,snow of the ,united ,states as compiled to the ,end of #ahia1 with ,annual1 ,seasonal1 ,monthly1 and other ,charts4 ,,mark ,w4 ,,harrington4 ,united ,states ,department of ,agriculture4 ,weather ,bureau1 ,bulletin ,c1 ,washington1 ,d4 ,c4 #ahid4 ,atlas1 #ah #bd inches4 ,charts #bc4 ,text1 #d-hj pp4 ,contains twenty-three charts as follows3 ,monthly rainfall1 seasonal rainfall1 annual rainfall1 monthly snowfall1 monthly maxima of rainfall1 rainy seasons1 details of rainfall1 details of occurrence of thunderstorms4 ,well adapted to serve as illustrations for use in the class-room4 ,the text is explanatory1 and is published separately in quarto form4 ,rainfall of the ,united ,states1 with ,annual1 ,seasonal1 and other ,charts4 ,,alfred ,j4 ,,henry4 ,united ,states ,department of ,agriculture1 ,weather ,bureau1 ,bulletin ,d1 ,washington1 ,d4 ,c4 #ahig4 #i-a_/d #aa-a_/b inches4 ,pp4 #eh4 ,charts #aj4 ,plates ,,iii4 ,a more recent publication than the preceding one1 the averages having been compiled to the end of #ahif4 ,the charts are smaller than most of those in ,bulletin ,c1 and therefore not so well adapted for class-room illustration4 ,the chart of mean annual precipitation is the latest and best published4 ,the rainfall of the crop-growing season receives separate treatment1 and is illustrated by means of two charts4 ,the discussion in the text is excellent4 ,f4 ,,meteorological ,,tables4 ,smithsonian ,meteorological ,tables4 ,smithsonian ,miscellaneous ,collections1 #hdd4 ,washington1 ,d4 ,c4 #ahic4 #hvo4 ,pp4 #bfb4 ,a very complete set of tables4 ,handbook of ,meteorological ,tables4 ,h4 ,a4 ,,hazen 7of the ,united ,states ,weather ,bureau74 ,washington1 ,d4 ,c4 #ahhh4 #hvo4 ,pp4 #abg4 #a4ej4 ,contains forty-seven tables1 comprising all that are needed by the working meteorologist4 ,includes tables for ,fahrenheit and ,centigrade conversions1 for barometric hypsometry and reduction to sea level1 for the psychrometer1 etc4 ,tables for ,obtaining the ,temperature of the ,dew-,point1 ,relative ,humidity1 etc4 ,united ,states ,department of ,agriculture1 ,weather ,bureau1 ,washington1 ,d4 ,c4 #ahig4 #hvo4 ,pp4 #bi4 ,these are the tables now in use by the ,weather ,bureau4 ,g4 ,,illustrations4 ,classification of ,clouds for the ,weather ,observers of the ,hydrographic ,office4 ,hydrographic ,office1 ,bureau of ,navigation1 ,department of the ,navy1 ,washington1 ,d4 ,c4 #ahig4 ,sheet of twelve colored views4 ,price #dj cents4 ,in book form1 with descriptive text1 #a4jj4 ,an excellent set of cloud views1 classified according to the ,international ,nomenclature4 ,the text describes the various cloud forms and shows their value as weather prognostics4 ,an attractive addition to the furnishings of a schoolroom4 ,selected ,list of ,cloud ,photographs and ,lantern ,slides4 ,consists of twenty-eight photographs1 and the same number of lantern slides1 of the typical cloud forms1 selected by the present writer from the collection in the ,physical ,geography ,laboratory of ,harvard ,university4 ,the photographs 7#bj cents each1 mounted7 and slides 7#dj cents each7 may be purchased of ,e4 ,e4 ,howell1 #fab #agth ,street1 ,n4 ,w41 ,washington1 ,d4 ,c4 ,a description of these views was published in the ,american ,meteorological ,journal for ,july1 #ahid 7,boston1 ,mass41 ,ginn ,company74 ,photographs4 ,photographs of miscellaneous meteorological phenomena1 such as snow and ice storms1 damage by storm-waves or high winds1 wind-blown trees1 lightning1 etc41 may often be purchased of local dealers4 ,they add to the attractiveness of a schoolroom and furnish excellent illustrations in teaching4 ,h4 ,,general4 ,the following ,bulletins of the ,weather ,bureau may be found useful as reference books3 ,no4 #a4 ,notes on the ,climate and ,meteorology of ,death ,valley1 ,california4 ,,mark ,w4 ,,harrington4 #hvo4 #ahib4 ,pp4 #ej4 ,no4 #h4 ,report on the ,climatology of the ,cotton ,plant4 ,p4 ,h4 ,,mell4 #hvo4 #ahic4 ,pp4 #fh4 ,no4 #aj4 ,the ,climate of ,chicago4 ,h4 ,a4 ,,hazen4 #hvo4 #ahic4 ,pp4 #acg4 ,no4 #aa4 ,report of the ,international ,meteorological ,congress held at ,chicago1 ,,iii41 ,aug4 #ba-bd1 #ahic4 #hvo4 ,pt4 ,i1 #ahid1 pp4 #bjf4 ,pt4 ,,ii1 #ahie1 pp4 #ehc4 ,pt4 ,,iii1 #ahif1 pp4 #ggb4 ,pt4 ,,iv1 not yet issued4 ,no4 #ae4 ,protection from ,lightning4 ,,alexander ,,mcadie4 #hvo4 #ahie4 ,pp4 #bf4 ,no4 #ag4 ,the ,work of the ,weather ,bureau in ,connection with the ,rivers of the ,united ,states4 ,,willis ,l4 ,,moore4 #hvo4 #ahif4 ,pp4 #ajf4 ,no4 #ai4 ,report on the ,relative ,humidity of ,southern ,new ,england and ,other ,localities4 ,a4 ,j4 ,,henry4 #hvo4 #ahif4 ,pp4 #bc4 ,no4 #bj4 ,storms1 ,storm ,tracks and ,weather ,forecasting4 ,,frank ,h4 ,,bigelow4 #hvo4 #ahig4 ,pp4 #hg4 ,no4 #ba4 ,climate1 of ,cuba4 ,also1 ,a ,note on the ,weather of ,manila4 ,w4 ,f4 ,r4 ,,phillips4 #hvo4 #ahih4 ,pp4 #bc4 ,no4 #bc4 ,frost3 ,when to expect it and how to lessen the ,injury therefrom4 ,w4 ,h4 ,,hammon4 #hvo4 #ahii4 ,pp4 #cg4 ,no4 #be4 ,weather ,forecasting3 ,some ,facts ,historical1 ,practical1 and ,theoretical4 ,,willis ,l4 ,,moore4 #hvo4 #ahii4 ,pp4 #af4 ,no4 #bf4 ,lightning and the ,electricity of the ,air4 ,in two parts4 ,a4 ,g4 ,,mcadie and ,a4 ,j4 ,,henry4 #hvo4 #ahii4 ,pp4 #gd4 ,the following miscellaneous publications of the ,weather ,bureau may also prove of value4 ,injury from ,frost and ,methods of ,protection4 ,w4 ,h4 ,,hammon4 #hvo4 #ahif4 ,pp4 #ab4 ,some ,climatic ,features of the ,arid ,regions4 ,,willis ,l4 ,,moore4 #hvo4 #ahif4 ,pp4 #ai4 ,investigation of the ,cyclonic ,circulation and the ,translatory ,movement of the ,west ,indian ,hurricanes4 ,the late ,,rev4 ,,benito ,,vi,,es1 ,s4 ,j4 #hvo4 #ahih4 ,pp4 #cd4 ,requests for weather maps1 ,bulletins1 and other publications of the ,weather ,bureau should be sent to the ,chief of the ,weather ,bureau1 ,washington1 ,d4 ,c4 ,all requests are dealt with on their merits1 and in cases where it is deemed that effective use will be made of the publications they are usually sent free of charge4 ,,index4 ,a4 ,anemometer1 #ch-da4 ,aneroid barometer1 #bc1 #bd4 ,anticyclones1 #gf4 -------- and pressure changes1 #ada4 -------- and temperature1 #ajd-ajf4 -------- and weather1 #aji-aab4 -------- and wind circulation1 #ih-ajj4 -------- form and dimensions of1 #if-ih4 -------- progression of1 #aaa1 #aab4 -------- tracks of1 #aaa1 #aab4 ,b4 ,backing winds1 #aah4 ,barograph1 #cf1 #cg4 -------- records1 #cg1 #ch4 ,barometer1 aneroid1 #bc1 #bd4 -------- corrections1 #cc1 #cd4 -------- mercurial1 #ai-bc1 #cb1 #cc4 -------- reduction to freezing1 #adc1 #add1 #aff1 #afg4 ,barometer reduction to sea level1 #add1 #ade1 #afh-agj4 ,buran1 #ge1 #gf4 ,buys-,ballot's ,law1 #ii4 ,c4 ,cherrapunjee1 rainfall at1 #ach4 ,clouds and upper air currents1 #acf1 #acg4 ,clouds as weather prognostics1 #acg4 -------- forms and changes of1 #acf4 -------- movements of1 #da-dc1 #df1 #ie1 #acf1 #acg4 ,clouds1 observations of1 #e1 #i1 #da-dc1 #de1 #df4 ,cold wave1 #fb1 #ge1 #gf1 #ajc1 #ajf4 ,cold-wave forecasts1 #fc4 ,correlations of weather elements1 #ia-aac4 ,cyclones1 #gf4 -------- and pressure changes1 #ada4 -------- and temperature1 #ajd-ajf4 -------- and weather1 #aji-aaa1 #aac1 #aad4 -------- and wind circulation1 #ih-ajj4 -------- form and dimensions of1 #if-ih4 -------- progression of1 #aaa1 #aab4 -------- tracks of1 #aaa1 #aac4 -------- tropical1 #ajf4 -------- velocity of1 #aab1 #aac4 ,d4 ,dew1 #acd1 #acf4 -------- point1 #cj4 -------- -------- tables1 #adb1 #adc1 #adf-aee4 ,diurnal variation of temperature1 #abe-abg4 ,diurnal variation of wind velocity1 #acj4 ,doldrums1 #bi4 ,e4 ,equipment of a meteorological laboratory1 #ahf4 ,evaporation1 #bi4 ,f4 ,fahrenheit1 #ab1 #ac4 ,ferrel's ,law1 #ic4 ,forecasts1 cold-wave1 #fc4 -------- weather1 #di1 #aad-abd4 ,franklin1 ,benjamin1 #aad1 #aae4 ,frost1 #ace4 -------- warnings1 #ace4 ,g4 ,galileo1 #ab1 #ai4 ,gradients1 pressure1 #hb-he4 -------- temperature1 #fd-gj4 -------- vertical temperature1 #abi4 ,h4 ,humidity1 #bi1 #acb-acd4 -------- diurnal variation of1 #acc4 -------- relative1 #cj1 #cb1 #de1 #acc4 -------- relative1 and wind direction1 #acc4 -------- tables1 #adc1 #aef-afe4 ,hurricane1 #ajj4 ,i4 ,inversions of temperature1 #abi4 ,isobaric charts1 #gf-hb1 #he1 #ie1 #if4 ,isobars1 #gg-hb1 #aba4 ,isothermal charts1 #fc1 #fh-gj4 ,isotherms1 #ee-eg1 #aba4 ,l4 ,land and sea breezes1 #c1 #aca1 #acb4 ,loomis1 #ig1 #aac4 ,m4 ,meteorological tables1 #adf-agj4 ,mistral1 #ge4 ,monsoons1 #ajj4 ,mountain and valley winds1 #aca4 ,n4 ,nephoscope1 #da-dc4 ,o4 ,observational meteorology1 problems in1 #abe-ada4 ,observations1 advanced instrumental1 #bf-df4 ,observations1 cloud1 #e1 #i1 #da-dc4 -------- elementary instrumental1 #aa-bf4 ,observations1 non-instrumental1 #a-aj4 ,observations1 rainfall1 #i1 #aj1 #bf4 -------- state of sky1 #e1 #i4 -------- temperature1 #a-c1 #be4 -------- wind1 #c-e1 #h1 #i1 #be4 ,p4 ,pampero1 #gf1 #ajd4 ,pascal1 #ba4 ,precipitation1 #g1 #i1 #aj1 #ach1 #aci4 ,pressure and wind direction1 #ia-ic4 -------- and wind velocity1 #ic-if4 -------- atmospheric1 #ai-ba4 -------- charts1 #gf-hc4 -------- cyclonic variation of1 #adj1 #ada4 -------- decrease with altitude1 #aci1 #adj4 -------- diurnal variation of1 #adj1 #ada4 -------- gradient1 #hb-he4 ,prevailing westerly winds1 #ic1 #ie1 #if1 #aab1 #aac4 ,psychrometer1 #bh4 -------- sling1 #ca4 ,purga1 #ge4 ,r4 ,rain1 see ,precipitation4 -------- heavy1 #ach1 #aci4 -------- gauge1 #ae-ag4 ,rainfall records1 #ag1 #ah1 #bf4 ,s4 ,sensible temperatures1 #bi1 #cj4 ,sirocco1 #ajc1 #ajd1 #acc1 #acd4 ,sling psychrometer1 #ca4 ,smudges1 #ace4 ,state of sky1 #e1 #i1 #de4 ,suggestions to teachers1 #aga4 ,t4 ,temperature charts1 #eh-fj4 -------- distribution1 #ea-fc4 -------- diurnal range1 #abe-abg4 -------- forecasts1 #aaf4 -------- gradient1 #fd-gj4 ,temperature gradient1 vertical1 #abi4 -------- inversions1 #abi4 -------- maximum and minimum1 #de4 -------- mean1 #dc1 #de4 -------- observations1 #a-c1 #h-aj1 #be1 #dc1 #de4 -------- range1 #de1 #abe-abg4 -------- sensible1 #bi1 #cj4 -------- vertical distribution of1 #abh1 #abi4 ,thermograph1 #cd-cf4 -------- records1 #ce1 #cf4 ,thermometer1 #ab4 -------- attached1 #cc4 -------- maximum and minimum1 #bf-bh4 -------- shelter1 #ac1 #ad4 -------- wet- and dry-bulb1 #bh1 #cj1 #ca4 ,torricelli1 #ai1 #bj4 ,trade winds1 #ic4 ,v4 ,veering winds1 #aah4 ,vernier1 #cc4 ,vertical temperature gradient1 #abi4 ,w4 ,water vapor1 #bh4 ,weather1 #he-ij4 -------- and wind direction1 #ajf-aji4 -------- changes1 sequence of1 #aac1 #aad4 -------- charts1 #he-ij4 ,weather forecasts1 #di1 #aad-abd4 -------- map data1 #ij4 -------- maps1 #dg-ea4 -------- prognostics1 #acg4 -------- signs1 #he4 -------- temperate zone1 #hh-ij4 -------- torrid zone1 #hh-ij4 ,wind charts1 #gj-ge4 -------- direction and pressure1 #ia-ic4 -------- -------- and relative humidity1 #acc4 -------- -------- and temperature1 #aja-ajd4 -------- -------- and weather1 #ajf-aji4 -------- -------- forecasts of1 #aah4 -------- observations1 #c-e1 #be1 #dj1 #da4 -------- rose1 #ajc1 #ajh1 #aji4 -------- vane1 #ae4 -------- velocity1 #c1 #dj1 #da1 #de4 -------- -------- and pressure1 #ic-if4 -------- -------- diurnal variation of1 #acj4 -------- -------- forecasts of1 #aah4 -------- -------- scale1 #c4 ,winds around cyclones and anticyclones1 #ih-ajj4 ,winds1 mountain and valley1 #aca1 #acb4 -------- prevailing westerly1 #ic1 #ie-if1 #aab1 #aac4 ,winds1 trade1 #ic4 ,woeikof1 #fi4 99 99 99 99 99 ,,transcriber',s ,,amendments ,transcriber's ,note3 ,blank pages have been deleted4 ,some illustrations have been moved4 ,the footnotes have been coalesced and moved so as to follow the referencing paragraph4 ,the publisher's inadvertent omissions of important punctuation have been corrected4 ,some wide tables have been re-formatted to narrower equivalents with some words replaced with commonly known abbreviations and possibly a key4 ,the table on page #dd has been flipped around a diagonal axis so that the original column headings are now row headings4 ,the following list indicates any additional changes made4 ,the page number represents that of the original publication and applies in this etext except for footnotes and illustrations since they may have been moved4 ,key3 fromto3 ,page ,change #f ,than the day before yesterday8 #fb reduction of temperature to from #af to #cf4 #ge general relation between winds and cold wavewaves #aei #dg #dd #db #bici #cf #cd #ca #ec #afb #ajcajh #ig #ic #ij #hg #hc #hj #agj ,multiple unrecorded corrections4 99 99 99 99 99