,science ,primers4 ,,introductory4 ,,by ,,professor ,,huxley1 ,f4,r4,s4 ,toronto3 ,,canada ,,publishing ,,co41 7,,limited47 ,entered according to the ,act of the ,parliament of ,canada1 in the year ,one ,thousand ,eight ,hundred and ,eighty-one by ,,macmillan ,,co41 ,,london1 in the ,office of the ,minister of ,agriculture4 ,,table ,,of ,,contents4 ,,part4 ,,sect4 ,i4 ,,nature ,,and ,,science4 ,,page #a4 ,sensations and ,things #e #b4 ,causes and ,effects #e #c4 ,the reason ,why4 ,explanation #f #d4 ,properties and ,powers #g #e4 ,artificial and ,natural ,objects4 ,nature #h #f4 ,artificial ,things are only ,natural ,things shaped and brought together or separated by ,men #h #g4 ,many ,objects and ,chains of ,causes and ,effects in ,nature are out of our reach #aj #h4 ,the ,order of ,nature3 nothing happens by ,accident1 and there is no such thing as ,chance #aj #i4 ,laws of ,nature2 ,laws are not ,causes #ab #aj4 ,knowledge of ,nature is the ,guide of ,practical ,conduct #ad #aa4 ,science3 ,the ,knowledge of the ,laws of ,nature obtained by ,observation1 ,experiment1 and ,reasoning #af ,,ii4 ,,material ,,objects4--7,a47 ,,mineral ,,bodies4 #ab4 ,the ,natural ,object ,water #ai #ac4 ,a ,tumbler of ,water #bj #ad4 ,water occupies ,space2 it offers ,resistance2 it has ,weight2 and is able to transfer ,motion which it has acquired2 it is therefore a form of ,matter #bj #ae4 ,water is a liquid #ba #af4 ,water is almost incompressible #bb #ag4 ,the meaning of ,weight #bd #ah4 ,gravity and ,gravitation #be #ai4 ,the cause of ,weight3 ,attraction3 ,force #bg #bj4 ,the ,weight of ,water is ,proportioned to its ,bulk #bh #ba4 ,the ,measuring of ,weights4 ,the ,balance #bi #bb4 ,the ,weight of the same ,bulk or ,volume of ,water is ,constant under the same conditions4 ,mass4 ,density #cj #bc4 ,equal ,volumes of ,different ,things under the same circumstances1 have ,different ,weights3 the ,density of ,different ,bodies is ,different #cb #bd4 ,the ,meaning of ,heavy and ,light--,specific ,gravity #cc #be4 ,things of greater ,specific ,gravity than ,water sink in ,water2 ,things of less ,specific ,gravity float #cd #bf4 ,a ,body which ,floats in ,water always occupies as much ,space beneath the level of the ,surface of the ,water as is equal to the ,volume of ,water which weighs as much as that ,body2 in other words1 it displaces its own ,weight of ,water #cf #bg4 ,water ,presses in all ,directions #cg #bh4 ,the ,transference of ,motion by ,moving ,water3 the ,momentum of ,moving ,water #dj #bi4 ,the ,energy of ,moving ,water #dc #cj4 ,the ,properties of ,water are ,constant #dg #ca4 ,increase of ,heat at first causes ,water to ,increase in ,volume #dh #cb4 ,increase of ,heat at length causes ,water to become ,steam #ej #cc4 ,the taking away of ,heat from ,steam causes the ,steam to change into ,hot ,water #ea #cd4 ,when ,water is changed into ,steam1 its ,volume becomes about #a1gjj times greater than it was at first #ea #ce4 ,gases or ,elastic ,fluids4 ,air #eb #cf4 ,steam is an ,elastic ,fluid or ,gas #ed #cg4 ,gases and ,vapours #ee #ch4 ,the ,evaporation of ,water at ordinary ,temperatures #ef #ci4 ,when ,hot ,water is cooled1 it ,contracts to begin with1 but after a time ,expands #eg #dj4 ,water cooled still further becomes the transparent brittle solid ,ice #eh #da4 ,ice has less ,specific ,gravity than the ,water from which it was formed #ei #db4 ,hoar ,frost is the ,gaseous ,water which exists in the ,atmosphere1 condensed and converted into ,ice ,crystals #fj #dc4 ,when ,ice is warmed it begins to change back into ,water as soon as the ,temperature reaches #cb #fa #dd4 ,ice the solid1 ,water the liquid1 and ,steam the gas1 are three states of one natural object2 the ,condition of each ,state being a certain ,amount of ,heat #fb #de4 ,the ,phenomena of ,heat are the ,effects of a rapid ,motion of the ,particles of ,matter #fc #df4 ,the ,structure of ,water #fe #dg4 ,suppositions or ,hypotheses2 their ,uses and their ,value #fg #dh4 ,the ,hypothesis that ,water is composed of ,separate ,particles 7,molecules7 #fh #di4 ,all ,matter is probably made up either of ,molecules or of ,atoms #gj #ej4 ,elementary ,bodies are neither destroyed nor is their ,quantity increased in ,nature #gb #ea4 ,simple ,mixture #gc #eb4 ,mixture followed by ,increase of ,density2 ,alcohol and ,water #gd #ec4 ,solution2 ,water ,dissolves ,salt #gf #ed4 ,quicklime and ,water3 ,plaster of ,paris and ,water3 ,combination #gi #ee4 ,mineral bodies may take on definite shapes and grow1 or increase in size1 by the addition of like parts #hb 7,b47 ,,living ,,bodies4 #ef4 ,the ,wheat ,plant and the substances of which it is composed #hc #eg4 ,the common ,fowl and the ,substances of which it is ,composed #he #eh4 ,certain ,constituents of the ,body are very similar in the ,wheat ,plant and in the ,fowl #hf #ei4 ,proteid ,substances are met with in ,nature only in ,animals and ,plants2 and ,animals and ,plants always contain ,proteids #hg #fj4 ,what is meant by the word ,living8 #hh #fa4 ,the ,living ,plant increases in ,size1 by adding to the ,substances which compose its ,body1 like ,substances2 these1 however1 are not derived from without1 but are manufactured within the ,body of the ,plant from simpler ,materials #hh #fb4 ,the ,living ,plant1 after it has grown up1 detaches part of its ,substance1 which has the ,power of developing into a similar ,plant1 as a ,seed #ij #fc4 ,the ,living ,animal increases in ,size by adding to the ,substances which compose its ,body1 like ,substances2 these1 however1 are chiefly derived directly from other ,animals or from ,plants #ij #fd4 ,the living ,animal1 after it has grown up1 detaches part of its ,substance1 which has the ,power of growing into a similar ,animal1 as an ,egg #ia #fe4 ,living ,bodies differ from ,mineral ,bodies in their ,essential ,composition1 in the manner of their ,growth1 and in the fact that they are reproduced by ,germs #ia ,,iii4 ,,immaterial ,,objects4 #ff4 ,mental ,phenomena #ib #fg4 ,the order of ,mental ,phenomena3 ,psychology #ic ,,science ,,primers4 ,,introductory4 ,i4 ,,nature ,,and ,,science4 #a4 ,sensations and ,things4 ,all the time that we are awake we are learning by means of our senses something about the world in which we live and of which we form a part2 we are constantly aware of feeling1 or hearing1 or smelling1 and1 unless we happen to be in the dark1 of seeing2 at intervals we taste4 ,we call the information thus obtained sensation4 ,when we have any of these sensations we commonly say that we feel1 or hear1 or smell1 or see1 or taste1 something4 ,a certain scent makes us say we smell onions2 a certain flavour1 that we taste apples2 a certain sound1 that we hear a carriage2 a certain appearance before our eyes1 that we see a tree2 and we call that which we thus perceive by the aid of our senses a thing or an object4 #b4 ,causes and ,effects4 ,moreover1 we say of all these things1 or objects1 that they are the causes of the sensations in question1 and that the sensations are the effects of these causes4 ,for example1 if we hear a certain sound1 we say it is caused by a carriage going along the road1 or that it is the effect1 or the consequence1 of a carriage passing along4 ,if there is a strong smell of burning1 we believe it to be the effect of something on fire1 and look about anxiously for the cause of the smell4 ,if we see a tree1 we believe that there is a thing or object1 which is the cause of that appearance in our field of view4 #c4 ,the reason ,why4 ,explanation4 ,in the case of the smell of burning1 when we find on looking about1 that something actually is on fire1 we say indifferently either that we have found out the cause of the smell1 or that we know the reason why we perceive that smell2 or that we have explained it4 ,so that to know the reason why of anything1 or to explain it1 is to know the cause of it4 ,but that which is the cause of one thing is the effect of another4 ,thus1 suppose we find some smouldering straw to be the cause of the smell of burning1 we immediately ask what set it on fire1 or what is the cause of its burning8 ,perhaps we find that a lighted lucifer match has been thrown into the straw1 and then we say that the lighted match was the cause of the fire4 ,but a lucifer match would not be in that place unless some person had put it there4 ,that is to say1 the presence of the lucifer match is an effect produced by somebody as cause4 ,so we ask why did any one put the match there8 ,was it done carelessly1 or did the person who put it there intend to do so8 ,and if so1 what was his motive1 or the cause which led him to do such a thing8 ,and what was the reason for his having such a motive8 ,it is plain that there is no end to the questions1 one arising out of the other1 that might be asked in this fashion4 ,thus we believe that everything is the effect of something which preceded it as its cause1 and that this cause is the effect of something else1 and so on1 through a chain of causes and effects which goes back as far as we choose to follow it4 ,anything is said to be explained as soon as we have discovered its cause1 or the reason why it exists2 the explanation is fuller1 if we can find out the cause of that cause2 and the further we can trace the chain of causes and effects1 the more satisfactory is the explanation4 ,but no explanation of anything can be complete1 because human knowledge1 at its best1 goes but a very little way back towards the beginning of things4 #d4 ,properties and ,powers4 ,when a thing is found always to cause a particular effect1 we call that effect sometimes a property1 sometimes a power of the thing4 ,thus the odor of onions is said to be a property of onions1 because onions always cause that particular sensation of smell to arise1 when they are brought near the nose2 lead is said to have the property of heaviness1 because it always causes us to have the feeling of weight when we handle it2 a stream is said to have the power to turn a water-wheel1 because it causes the water-wheel to turn2 and a venomous snake is said to have the power to kill a man1 because its bite may cause a man to die4 ,properties and powers1 then1 are certain effects caused by the things which are said to possess them4 #e4 ,artificial and ,natural ,objects4 ,nature4 ,a great many of the things brought to our knowledge by our senses1 such as houses and furniture1 carriages and machines1 are termed artificial things or objects1 because they have been shaped by the art of man2 indeed1 they are generally said to be made by man4 ,but a far greater number of things owe nothing to the hand of man1 and would be just what they are if mankind did not exist1--such as the sky and the clouds2 the sun1 moon and stars2 the sea with its rocks and shingly or sandy shores2 the hills and dales of the land2 and all wild plants and animals4 ,things of this kind are termed natural objects1 and to the whole of them we give the name of ,nature4 #f4 ,artificial ,things are only ,natural ,things shaped and brought together or separated by ,men4 ,although this distinction between nature and art1 between natural and artificial things1 is very easily made and very convenient1 it is needful to remember that1 in the long run1 we owe everything to nature2 that even those artificial objects which we commonly say are made by men1 are only natural objects shaped and moved by men2 and that1 in the sense of creating1 that is to say1 of causing something to exist which did not exist in some other shape before1 man can make nothing whatever4 ,moreover1 we must recollect that what men do in the way of shaping and bringing together or separating natural objects1 is done in virtue of the powers which they themselves possess as natural objects4 ,artificial things are1 in fact1 all produced by the action of that part of nature which we call mankind1 upon the rest4 ,we talk of 8making0 a box1 and rightly enough1 if we mean only that we have shaped the pieces of wood and nailed them together2 but the wood is a natural object and so is the iron of the nails4 ,a watch is 8made0 of the natural objects gold and other metals1 sand1 soda1 rubies1 brought together1 and shaped in various ways2 a coat is 8made0 of the natural object1 wool2 and a frock of the natural objects1 cotton or silk4 ,moreover1 the men who make all these things are natural objects4 ,carpenters1 builders1 shoemakers1 and all other artisans and artists1 are persons who have learned so much of the powers and properties of certain natural objects1 and of the chain of causes and effects in nature1 as enables them to shape and put together those natural objects1 so as to make them useful to man4 ,a carpenter could not1 as we say1 8make0 a chair unless he knew something of the properties and powers of wood2 a blacksmith could not 8make0 a horseshoe unless he knew that it is a property of iron to become soft and easily hammered into shape when it is made red-hot2 a brickmaker must know many of the properties of clay2 and a plumber could not do his work unless he knew that lead has the properties of softness and flexibility1 and that a moderate heat causes it to melt4 ,so that the practice of every art implies a certain knowledge of natural causes and effects2 and the improvement of the arts depends upon our learning more and more of the properties and powers of natural objects1 and discovering how to turn the properties and the powers of things and the connections of cause and effect among them to our own advantage4 #g4 ,many ,objects and ,chains of ,causes and ,effects in ,nature are out of our reach4 ,among natural objects1 as we have seen1 there are some that we can get hold of and turn to account4 ,but all the greatest things in nature and the links of cause and effect which connect them1 are utterly beyond our reach4 ,the sun rises and sets2 the moon and the stars move through the sky2 fine weather and storms1 cold and heat1 alternate4 ,the sea changes from violent disturbance to glassy calm1 as the winds sweep over it with varying strength or die away2 innumerable plants and animals come in being and vanish again1 without our being able to exert the slightest influence on the majestic procession of the series of great natural events4 ,hurricanes ravage one spot2 earthquakes destroy another2 volcanic eruptions lay waste a third4 ,a fine season scatters wealth and abundance here1 and a long drought brings pestilence and famine there4 ,in all such cases1 the direct influence of man avails him nothing2 and1 so long as he is ignorant1 he is the mere sport of the greater powers of nature4 #h4 ,the ,order of ,nature3 nothing happens by ,accident1 and there is no such thing as ,chance4 ,but the first thing that men learned1 as soon as they began to study nature carefully1 was that some events take place in regular order and that some causes always give rise to the same effects4 ,the sun always rises on one side and sets on the other side of the sky2 the changes of the moon follow one another in the same order and with similar intervals2 some stars never sink below the horizon of the place in which we live2 the seasons are more or less regular2 water always flows down-hill2 fire always burns2 plants grow up from seed and yield seed1 from which like plants grow up again2 animals are born1 grow1 reach maturity1 and die1 age after age1 in the same way4 ,thus the notion of an order of nature and of a fixity in the relation of cause and effect between things gradually entered the minds of men4 ,so far as such order prevailed it was felt that things were explained2 while the things that could not be explained were said to have come about by chance1 or to happen by accident4 ,but the more carefully nature has been studied1 the more widely has order been found to prevail1 while what seemed disorder has proved to be nothing but complexity2 until1 at present1 no one is so foolish as to believe that anything happens by chance1 or that there are any real accidents1 in the sense of events which have no cause4 ,and if we say that a thing happens by chance1 everybody admits that all we really mean is1 that we do not know its cause or the reason why that particular thing happens4 ,chance and accident are only aliases of ignorance4 ,at this present moment1 as ,i look out of my window1 it is raining and blowing hard1 and the branches of the trees are waving wildly to and fro4 ,it may be that a man has taken shelter under one of these trees2 perhaps1 if a stronger gust than usual comes1 a branch will break1 fall upon the man1 and seriously hurt him4 ,if that happens it will be called an 8accident10 and the man will perhaps say that by 8chance0 he went out1 and then 8chanced0 to take refuge under the tree1 and so the 8accident0 happened4 ,but there is neither chance nor accident in the matter4 ,the storm is the effect of causes operating upon the atmosphere1 perhaps hundreds of miles away2 every vibration of a leaf is the consequence of the mechanical force of the wind acting on the surface exposed to it2 if the bough breaks1 it will do so in consequence of the relation between its strength and the force of the wind2 if it falls upon the man it will do so in consequence of the action of other definite natural causes2 and the position of the man under it is only the last term in a series of causes and effects1 which have followed one another in natural order1 from that cause1 the effect of which was his setting out1 to that the effect of which was his stepping under the tree4 ,but1 inasmuch as we are not wise enough to be able to unravel all these long and complicated series of causes and effects which lead to the falling of the branch upon the man1 we call such an event an accident4 #i4 ,laws of ,nature2 ,laws are not ,causes4 ,when we have made out by careful and repeated observation that something is always the cause of a certain effect1 or that certain events always take place in the same order1 we speak of the truth thus discovered as a law of ,nature4 ,thus it is a law of nature that anything heavy falls to the ground if it is unsupported2 it is a law of nature that1 under ordinary conditions1 lead is soft and heavy1 while flint is hard and brittle2 because experience shows us that heavy things always do fall if they are unsupported1 that1 under ordinary conditions1 lead is always soft and that flint is always hard4 ,in fact1 everything that we know about the powers and properties of natural objects and about the order of nature may properly be termed a law of nature4 ,but it is desirable to remember that which is very often forgotten1 that the laws of nature are not the causes of the order of nature1 but only our way of stating as much as we have made out of that order4 ,stones do not fall to the ground in consequence of the law just stated1 as people sometimes carelessly say2 but the law is a way of asserting that which invariably happens when heavy bodies at the surface of the earth1 stones among the rest1 are free to move4 ,the laws of nature are1 in fact1 in this respect1 similar to the laws which men make for the guidance of their conduct towards one another4 ,there are laws about the payment of taxes1 and there are laws against stealing or murder4 ,but the law is not the cause of a man's paying his taxes1 nor is it the cause of his abstaining from theft and murder4 ,the law is simply a statement of what will happen to a man if he does not pay his taxes1 and if he commits theft or murder2 and the cause of his paying his taxes1 or abstaining from crime 7in the absence of any better motive7 is the fear of consequences which is the effect of his belief in that statement4 ,a law of man tells what we may expect society will do under certain circumstances2 and a law of nature tells us what we may expect natural objects will do under certain circumstances4 ,each contains information addressed to our intelligence1 and except so far as it influences our intelligence1 it is merely so much sound or writing4 ,while there is this much analogy between human and natural laws1 however1 certain essential differences between the two must not be overlooked4 ,human law consists of commands addressed to voluntary agents1 which they may obey or disobey2 and the law is not rendered null and void by being broken4 ,natural laws1 on the other hand1 are not commands but assertions respecting the invariable order of nature2 and they remain laws only so long as they can be shown to express that order4 ,to speak of the violation1 or the suspension1 of a law of nature is an absurdity4 ,all that the phrase can really mean is that1 under certain circumstances the assertion contained in the law is not true2 and the just conclusion is1 not that the order of nature is interrupted1 but that we have made a mistake in stating that order4 ,a true natural law is an universal rule1 and1 as such1 admits of no exceptions4 ,again1 human laws have no meaning apart from the existence of human society4 ,natural laws express the general course of nature1 of which human society forms only an insignificant fraction4 #aj4 ,knowledge of ,nature is the ,guide of ,practical ,conduct4 ,if nothing happens by chance1 but everything in nature follows a definite order1 and if the laws of nature embody that which we have been able to learn about the order of nature in accurate language1 then it becomes very important for us to know as many as we can of these laws of nature1 in order that we may guide our conduct by them4 ,any man who should attempt to live in a country without reference to the laws of that country would very soon find himself in trouble2 and if he were fined1 imprisoned1 or even hanged1 sensible people would probably consider that he had earned his fate by his folly4 ,in like manner1 any one who tries to live upon the face of this earth without attention to the laws of nature will live there for but a very short time1 most of which will be passed in exceeding discomfort2 a peculiarity of natural laws1 as distinguished from those of human enactment1 being that they take effect without summons or prosecution4 ,in fact1 nobody could live for half a day unless he attended to some of the laws of nature2 and thousands of us are dying daily1 or living miserably1 because men have not yet been sufficiently zealous to learn the code of nature4 ,it has already been seen that the practice of all our arts and industries depends upon our knowing the properties of natural objects which we can get hold of and put together2 and though we may be able to exert no direct control over the greater natural objects and the general succession of causes and effects in nature1 yet1 if we know the properties and powers of these objects1 and the customary order of events1 we may elude that which is injurious to us1 and profit by that which is favourable4 ,thus1 though men can nowise alter the seasons or change the process of growth in plants1 yet having learned the order of nature in these matters1 they make arrangements for sowing and reaping accordingly2 they cannot make the wind blow1 but when it does blow they take advantage of its known powers and probable direction to sail ships and turn windmills2 they cannot arrest the lightning1 but they can make it harmless by means of conductors1 the construction of which implies a knowledge of some of the laws of that electricity1 of which lightning is one of the manifestations4 ,forewarned is forearmed1 says the proverb2 and knowledge of the laws of nature is forewarning of that which we may expect to happen1 when we have to deal with natural objects4 #aa4 ,science3 the ,knowledge of the ,laws of ,nature obtained by ,observation1 ,experiment1 and ,reasoning4 ,no line can be drawn between common knowledge of things and scientific knowledge2 nor between common reasoning and scientific reasoning4 ,in strictness all accurate knowledge is ,science2 and all exact reasoning is scientific reasoning4 ,the method of observation and experiment by which such great results are obtained in science1 is identically the same as that which is employed by every one1 every day of his life1 but refined and rendered precise4 ,if a child acquires a new toy1 he observes its character and experiments upon its properties2 and we are all of us constantly making observations and experiments upon one thing or another4 ,but those who have never tried to observe accurately will be surprised to find how difficult a business it is4 ,there is not one person in a hundred who can describe the commonest occurrence with even an approach to accuracy4 ,that is to say1 either he will omit something which did occur1 and which is of importance2 or he will imply or suggest the occurrence of something which he did not actually observe1 but which he unconsciously infers must have happened4 ,when two truthful witnesses contradict one another in a court of justice1 it usually turns out that one or other1 or sometimes both1 are confounding their inferences from what they saw with that which they actually saw4 ,a swears that ,b picked his pocket4 ,it turns out that all that ,a really knows is that he felt a hand in his pocket when ,b was close to him2 and that ,b was not the thief1 but ,c1 whom ,a did not observe4 ,untrained observers mix up together their inferences from what they see with that which they actually see in the most wonderful way2 and even experienced and careful observers are in constant danger of falling into the same error4 ,scientific observation is such as is at once full1 precise1 and free from unconscious inference4 ,experiment is the observation of that which happens when we intentionally bring natural objects together1 or separate them1 or in any way change the conditions under which they are placed4 ,scientific experiment1 therefore1 is scientific observation performed under accurately known artificial conditions4 ,it is a matter of common observation that water sometimes freezes4 ,the observation becomes scientific when we ascertain under what exact conditions the change of water into ice takes place4 ,the commonest experiments tell us that wood floats in water4 ,scientific experiment shows that1 in floating1 it displaces its own weight of the water4 ,scientific reasoning differs from ordinary reasoning in just the same way as scientific observation and experiment differ from ordinary observation and experiment--that is to say1 it strives to be accurate2 and it is just as hard to reason accurately as it is to observe accurately4 ,in scientific reasoning general rules are collected from the observation of many particular cases2 and1 when these general rules are established1 conclusions are deduced from them1 just as in every-day life4 ,if a boy says that 8marbles are hard10 he has drawn a conclusion as to marbles in general from the marbles he happens to have seen and felt1 and has reasoned in that mode which is technically termed induction4 ,if he declines to try to break a marble with his teeth1 it is because he consciously1 or unconsciously1 performs the converse operation of deduction from the general rule 8marbles are too hard to break with one's teeth40 ,you will learn more about the process of reasoning when you study ,logic1 which treats of that subject in full4 ,at present1 it is sufficient to know that the laws of nature are the general rules respecting the behaviour of natural objects1 which have been collected from innumerable observations and experiments2 or1 in other words1 that they are inductions from those observations and experiments4 ,the practical and theoretical results of science are the products of deductive reasoning from these general rules4 ,thus science and common sense are not opposed1 as people sometimes fancy them to be1 but science is perfected common sense4 ,scientific reasoning is simply very careful common reasoning1 and common knowledge grows into scientific knowledge as it becomes more and more exact and complete4 ,the way to science then lies through common knowledge2 we must extend that knowledge by careful observation and experiment1 and learn how to state the results of our investigations accurately1 in general rules or laws of nature2 finally1 we must learn how to reason accurately from these rules1 and thus arrive at rational explanations of natural phenomena1 which may suffice for our guidance in life4 ,,ii4 ,,material ,,objects4--,a4 ,,mineral ,,bodies4 #ab4 ,the ,natural ,object ,water4 ,one of the commonest of common natural objects is water2 everybody uses it in one way or another every day2 and consequently everybody possesses a store of loose information--of common knowledge--about it4 ,but1 in all probability1 a great deal of this knowledge has never been attended to by its possessor2 and certainly1 those who have never tried to learn how much may be known about water1 will be ignorant of a great many of its powers and properties and of the laws of nature which it illustrates2 and consequently will be unable to account for many things of which the explanation is very easy4 ,so we may as well make a beginning of science by studying water4 #ac4 ,a ,tumbler of ,water4 ,suppose we have a tumbler half-full of water4 ,the tumbler is an artificial object 7 #e72 that is to say1 certain natural objects have been brought together and heated till they melted into glass1 and this glass has been shaped by a workman4 ,the water1 on the other hand1 is a natural object1 which has come from some river1 pond1 or spring2 or it may be from a water-butt into which the rain which has fallen on the roof of a house has flowed4 ,now the water has a vast number of peculiarities4 ,for example1 it is transparent1 so that you can see through it2 it feels cool2 it will quench thirst and dissolve sugar4 ,but these are not the characters which it is most convenient to begin with4 #ad4 ,water occupies ,space2 it offers ,resistance2 it has ,weight2 and is able to transfer ,motion which it has acquired2 it is therefore a form of ,matter4 ,the water1 we see1 fills the cavity of the tumbler for half its height1 therefore it occupies that much space1 or has that bulk or volume4 ,if you put the closed end of another tumbler of almost the same size into the first1 you will find that when it reaches the water1 the latter offers a resistance to its going down1 and unless some of the water can get out1 the end of the second tumbler will not go in4 ,any one who falls from a height into water will find that he receives a severe shock when he reaches it4 ,water therefore offers resistance4 ,if the water is emptied out1 the tumbler feels much lighter than it was before2 water1 therefore1 has weight4 ,and1 finally1 if you throw the water out of the tumbler at any slightly supported object1 the water hitting against it would knock it over4 ,that is to say1 the water being put in motion is able to transfer that motion to something else4 ,all these phenomena1 as things which happen in nature are often called1 are effects of which water1 under the conditions mentioned1 is the cause1 and they may therefore be said to be properties 7 #d7 of water4 ,all things which occupy space1 offer resistance1 possess weight and transfer motion to other things when they strike against them1 are termed material substances or bodies1 or simply matter4 ,water1 therefore1 is a kind1 or form1 of matter4 #ae4 ,water is a liquid4 ,you will easily observe that1 though water occupies space1 it has no definite shape1 but fits itself exactly to the figure of the vessel which holds it4 ,if the tumbler is cylindrical1 the contour of the surface of the water will be circular when the tumbler is held vertically1 and will change1 without the least break or interruption1 to more and more of an oval when the tumbler is inclined1 and whatever the shape of the vessel into which you pour it1 the sides of the water always exactly fit against the sides of the vessel4 ,if you put your finger into the water you can move it in all directions with scarcely any feeling of obstacle4 ,if you pull your finger out there is no hole left1 the water on all sides rushing together to fill up the space that was occupied by the finger4 ,you cannot take up a handful of water1 for it runs away between your fingers1 and you cannot raise it into a permanent heap4 ,all this shows that the parts of water move upon one another with great ease4 ,the same fact is illustrated if the tumbler is inclined so that the level of the surface rises above the edge of the tumbler on one side1 and the water is therefore to some extent unsupported by the tumbler at this point4 ,the water then flows over in a stream and falls to the ground1 where it spreads out and runs to the lowest accessible place1 or gradually soaks up into crevices4 ,nevertheless1 although the parts of the water thus loosely slip and slide upon one another1 yet they hold together to a certain extent4 ,if the surface of the water is just touched with the finger1 a little of it will adhere2 and if the finger is then slowly and carefully raised1 the adjacent water will be raised up into a slender column which acquires a noticeable length before it breaks4 ,so1 in the early morning1 after heavy dew1 you may see the water upon cabbage-leaves and blades of grass in spherical drops1 the parts of which similarly hold together4 ,material substances1 the parts of which are so movable that they fit themselves exactly to the sides of any vessel which contains them1 and which flow when they are not supported1 are called fluids1 and fluids the parts of which do not fly off from one another1 but hold together as those of water do1 are called liquids4 ,water therefore is a liquid4 #af4 ,water is almost incompressible4 ,it has been seen that water1 like every other material substance1 resists the intrusion of other matter into the place which it occupies4 ,but many things1 though they resist1 can be easily squeezed or compressed into a smaller volume4 ,this1 however1 is not the case with water1 which like other liquids1 is almost incompressible2 that is to say1 an immense pressure is needful to cause its volume to diminish to any appreciable extent4 ,it may seem strange that anything so apparently yielding as water should yet be almost as difficult to squeeze as so much iron2 but the apparent yieldingness of water is due to the ease with which it changes its shape2 and1 if water is prevented from changing its shape1 it is very difficult to drive its parts closer together4 ,it has been ascertained that if water is confined in a closed space1 a pressure amounting to fifteen pounds on the square inch diminishes its volume by only #a_/bjjjjth part4 ,take a common syringe1 and having seen that the plug or piston fits the cylinder of the syringe well1 put the nozzle into water and draw the piston up4 ,then turn the nozzle upward and push upon the piston till a little of the water squirts out1 so as to make sure that the cylinder contains nothing but water4 ,now put your finger on the opening of the nozzle firmly1 so as to stop any water from passing out1 and then try to push the piston down4 ,you will find that you cannot make it stir without great force2 and1 if the piston moves appreciably1 it will be because some of the water has escaped by the sides of the piston4 ,in fact1 if the piston presented a square inch of surface1 and fitted accurately1 and the column of water in the cylinder were one inch long1 it must be pressed down by a weight of #cj1jjj pounds 7about thirteen tons7 to make it move one-tenth of an inch4 #ag4 ,the ,meaning of ,weight4 ,let us next consider the property of weight4 ,we say that anything has weight when1 on trying to lift it from the ground1 or on holding it in the hand1 we have a feeling of effort4 ,or again1 if anything which is supported at a certain height above the ground1 falls when the support is taken away1 we say that it has weight4 ,now the ground merely means the surface of the earth2 and1 as all bodies which possess weight fall directly towards the surface of the earth when they are not kept away from it by some support1 we may say that all bodies which have weight tend to fall in this way4 ,and it does not matter on what part of the surface of the earth you make the experiment4 ,rain consists of drops of water1 and it does not matter whether we watch a shower in calm weather here1 or in ,new ,zealand2 the drops fall perpendicularly towards the ground4 ,but we know that the earth is a globe1 and that ,new ,zealand is at our antipodes1 or on the opposite side of the globe to ,england4 ,hence if two showers are falling at the same time1 one in ,new ,zealand and one here--the drops must be falling in opposite directions1 towards one another2 that is1 towards the centre of the earth which lies between them4 ,in fact1 all bodies which have weight tend to fall towards the centre of the earth--that is to say they fall in this way if there is nothing to prevent them2 and when we speak of weight we mean this tendency to fall4 ,to call anything heavy1 is the same as saying that we fully expect that1 if there is nothing to support it1 it will fall to the ground2 or that if we support it ourselves we shall be conscious of effort4 #ah4 ,gravity and ,gravitation4 ,the word gravity1 when it was first used1 had exactly the same meaning as weight2 and a body which has weight is said to gravitate towards the center of the earth4 ,but gravity has now acquired a much wider sense than weight4 ,for an immense number of careful observations and experiments have established the general rule1 or law of nature1 that every material substance1 tends to approach every other material substance1 just in the same way as a drop of rain falls towards the earth2 and1 in fact1 that any two portions of matter1 whatever the nature of that matter may be1 will move towards one another if there is nothing to prevent them from doing so4 ,to make this clear1 let us suppose that the only material bodies in the universe were two spherical drops of water1 each a tenth of an inch in diameter4 ,each of these drops would have the same bulk as the other1 and would be a quantity of matter exactly equivalent to the other4 ,then1 however great the distance which separated these two drops1 they would begin to approach one another2 and1 each moving with gradually increasing swiftness1 they would at length meet in a point exactly half-way between the positions which they at first occupied4 ,but if the bulk of one drop were greater than that of the other drop1 then the larger would move more slowly1 and the point of meeting would be by so much nearer the larger drop4 ,it follows that1 if the one body of water were as big as the earth and the other remained of its original size1 no bigger than a rain-drop--the motion of the large mass towards the small one would be an inconceivably minute fraction of the total distance travelled over4 ,it would appear as if the large body were perfectly still and drew the small body to itself4 ,this is just what happens when a single drop of water falls from a cloud1 say through a distance of a mile1 to the earth4 ,the earth really moves towards it1 just as it moves towards the earth1 on the straight line which joins the centres of the two4 ,but the length of this line which each travels over is inversely proportional to the quantity of matter in each1 that is to say is the less the bigger the quantity4 ,so that we have a rule-of-three sum4 ,as the quantity of matter in the earth is to that in a rain-drop1 so is a mile to the distance travelled over by the earth4 ,and if any one worked out this sum1 he would find that the fourth term of the proportion would be an inconceivably minute fraction of an inch4 ,for all practical purposes1 therefore1 we may consider the earth to be at rest in relation to all falling bodies1 inasmuch as the quantity of matter in any falling body is insignificant1 in comparison with that contained in the earth4 ,what is true of water is true1 so far as we know1 of all kinds of matter1 and we therefore say that it is a law of nature that all kinds of matter possess gravity2 that is to say1 that of any two1 each tends to move towards the other1 at a speed which is the slower the greater the quantity of matter it contains in proportion to that which the other contains2 and this speed gradually becomes quicker as the two bodies approach4 ,what is usually called the law of gravitation is a statement of the same observed facts in another and more complete fashion4 7,see ,physics ,primer47 #ai4 ,the cause of ,weight3 ,attraction3 ,force4 ,we know nothing whatever of the reason why bodies possess weight4 ,bodies do not fall on account of the law of gravitation 7 #i72 nor does their gravity explain why they fall4 ,gravity1 as we have seen1 is only a name for weight1 and the law of gravitation is only a statement of how bodies approach one another1 not why they do so4 ,it is often said that gravitation is attraction1 and that bodies fall to the earth because the earth attracts them4 ,but the word 8attract0 simply means to 8draw towards10 and 8attraction0 means nothing but 8drawing towards20 and to say1 when two bodies move towards one another1 that they are 8drawn towards0 one another1 is simply to describe the fact and makes us no whit wiser than we were before4 ,on the contrary1 unless we take great care1 it may make us a little less wise4 ,for the words 8drawing towards0 are so closely associated with ropes and hooks and the act of pulling1 that we are easily led to fancy the existence of some analogous invisible machinery in the case of mutually attractive bodies4 ,again1 gravitation is spoken of as a force2 and as the word force is in very common use1 let us try to make out what we mean by it4 ,a man is said to exert force when he pushes or pulls anything so as either to exert pressure upon it or to put it in motion4 ,a wrestler's force is proved by his hug2 a bowler's force is shown by the swiftness of motion of the ball4 ,force1 then1 is the name which we give to that which causes or1 in the case of pressure1 tends to cause1 motion4 ,the force of gravity therefore means the cause of the pressure which we feel when bodies which possess gravity are supported by our bodies1 and the cause of their movement towards the centre of the earth1 when they are free to move4 ,but it is exactly about the cause of these phenomena that we know nothing whatever4 ,a good deal of mischief is done by the inaccurate use of such words as attraction and force1 as if they were the names of things having an existence apart from natural objects1 and from the series of causes and effects which are open to our observation2 while they are1 in reality1 merely the names of the unknown causes of certain phenomena4 ,and it is worth while to take pains to get clear ideas on this head at the outset of the study of science4 ,let us remember then that1 so far as we know1 it is a law of nature1 that any two material bodies1 if they are free to move1 approach one another with gradually increasing swiftness2 and that the space over which each travels before the two meet1 is inversely proportional to the quantity of matter which it contains4 ,attraction of gravitation is a name for this general fact2 weight is the name for the fact in the case of terrestrial bodies2 force is a name which we give to the unknown cause of the fact4 ,the fact is that which it is important to know4 ,the names are of no great consequence so long as we recollect that they are merely names and not things4 #bj4 ,the ,weight of ,water is ,proportioned to its ,bulk4 ,we must next consider1 not weight in general1 but the weight of water4 ,we say that a tumbler full of water is heavier than an empty tumbler1 because the full tumbler gives us a greater feeling of effort when we lift it than the empty tumbler does4 ,the more water there is in the tumbler the greater is the effort4 ,a pail full of water requires still more effort1 though the empty pail feels quite light2 and1 when we come to deal with a large tub full of water1 we may be unable to stir it1 though the empty tub could be lifted with ease4 ,thus it seems that the greater the bulk of water the more it weighs1 and the less the bulk the less it weighs4 ,but then a single drop of water in the palm of the hand seems to weigh nothing at all4 ,however1 this clearly cannot be1 for the drop falls to the ground readily1 and therefore it must have weight4 ,moreover1 a few thousand drops would fill the tumbler1 and if a thousand drops weigh something1 each drop must have a thousandth of that weight4 ,the fact is that our feeling of effort is a very rough measure of weight1 and does not enable us to compare small weights1 or even to perceive them if they are very small4 ,to know anything accurately about weight we must have recourse to an instrument which is contrived for the purpose of measuring weights with precision4 #ba4 ,the ,measuring of ,weights4 ,the ,balance4 ,such an instrument is the balance or scales1 which you may see in every grocer's shop4 ,it is composed of a beam which moves easily on a pivot fixed to its middle1 and which has a scale-pan attached to each end4 ,so long as both scale-pans are empty the beam is horizontal2 but if you put anything which has weight into one1 that one goes down and the other rises4 ,if now you either pull or push the empty scale downwards1 the beam may be brought into the horizontal position again1 and the effort required to bring it into the horizontal position will be the greater1 the greater the weight of the body in the opposite scale4 ,an ounce in the one scale is easily raised by the pressure of a finger in the other4 ,a pound requires more effort2 ten pounds needs putting out the strength of the arm2 to raise fifty pounds involves still more exertion2 while a couple of hundredweight will not be stirred by the strongest push or pull upon the empty scale4 ,suppose that1 instead of pressing down the empty scale1 you put something that has weight into it2 then1 as soon as this weight is equal to that in the other scale1 the beam will become horizontal4 ,in fact1 one scale has just as much tendency to move towards the centre of the earth as the other has1 and as neither can go down without pulling the other up1 they neutralise one another4 ,it comes to the same thing1 as if two boys of equal strength were pulling one against the other2 so long as the pulls in opposite directions are equal1 of course neither boy can stir2 while the smallest addition of strength to one enables him to pull the other over4 #bb4 ,the ,weight of the same ,bulk or ,volume of ,water is ,constant under the same conditions4 ,mass4 ,density4 ,now let two graduated thin glass measures be put into the two scales1 and made to counterpoise one another exactly4 ,then1 if even a single drop of water is put into the one measure the scale will descend1 if the balance is a good one2 showing that the drop has weight4 ,if the measures are graduated accurately1 then whatever volume of water is put into one1 an exactly similar volume of the same water must be put into the other to make the beam level4 ,this obviously means that the same volume of water under the same circumstances always has the same weight4 ,in #ah it was said that bodies tend to move towards one another with a relative velocity#a which is inversely proportional to the quantity of matter which they contain4 ,but how are we to measure quantity of matter8 ,is it to be estimated by the space which it occupies2 that is1 by its volume8 or are we to estimate the quantity of matter in a body by its weight8 ,you will soon learn that the volume of all bodies is constantly changing in correspondence with the changes in the pressure exerted by other bodies1 but more especially in correspondence with the changes of temperature to which they are subjected2 while the weight of the same body1 at the same point on the earth's surface1 never alters4 ,hence we may take the weight of a body as a measure of the quantity of matter which it contains2 and it follows that1 for the same weight1 the larger the volume of a body the less matter it contains proportionally to its volume1 and the less the volume1 the more matter it contains4 ,the proportion of its weight to its volume gives us the density of a body4 ,footnote #a3 ,velocity1 or swiftness1 is measured by the distance over which a body travels1 in a given time4 ,of two bodies1 one of which travels through one foot in a second1 while the other travels through two feet1 the latter has the greater relative velocity4 ,now what is true of water is true of all other bodies or material substances4 ,suppose that one of the measures is emptied and replaced1 the beam may be brought to the horizontal position again by means of a piece of lead cut to exactly the right size4 ,the piece of lead will thenceforth furnish an exactly corresponding or equivalent weight for so much water2 and pieces of iron or brass1 which counterpoise the lead1 will also be equivalents of the weight of the water1 or of the lead1 or of one another4 ,but the pieces of lead1 iron1 or brass will obviously be of much less volume or bulk than the water which they counterpoise4 ,here it follows that the densities of these metals1 or the quantity of matter contained in the same volume1 must be much greater than in the case of water4 ,what are called weights in commerce are pieces of lead1 or iron1 or brass exactly equivalent in weight to a certain bulk of water under certain conditions4 ,an imperial gallon of water thus weighs ten pounds1 and therefore an imperial pint weighs a pound and a quarter4 #bc4 ,equal ,volumes of ,different ,things under the same circumstances1 have ,different ,weights3 the ,density of ,different ,bodies is ,different4 ,the important fact which has just been alluded to must be considered more fully4 ,we have seen that an imperial pint measure gives us the space which is taken up by as much water as weighs a pound and a quarter2 and this space is the bulk or volume of that weight of water4 ,but if you take an ordinary pound weight and a quarter-pound weight1 and put them into an imperial pint measure1 you will find that instead of filling it1 they take up only a very small portion of the space in its interior1 or in other words1 of its capacity4 ,thus the volume of a pound and a quarter of lead1 or of iron1 or of brass1 is very much less than the volume of the same weight of water2 that is to say1 the metals are denser than water2 the same volume has greater mass or more gravity4 ,or1 to put the case in another way1 fill the tumbler with which we began half full of water1 making a mark on the side exactly at the level of the top of the water4 ,then place it in one scale of a balance1 and counterpoise it with weights in the other4 ,next1 pour out the water1 and after drying the tumbler1 fill it with fine sand carefully up to the mark4 ,the volume of sand will be equal to the volume of water4 ,but now the same weights will no longer counterpoise it1 and you will have to put more weights in the opposite scale4 ,volume for volume1 therefore1 sand is heavier than water4 ,throw out the sand1 and put in sawdust in the same way1 and you will find that a less weight than was necessary to counterpoise the water counterpoises the sawdust4 ,volume for volume1 therefore1 sawdust is lighter than water4 ,experiment in the same way with spirit and oil1 and they will be found to be lighter than water1 while treacle will be heavier1 and quicksilver very much heavier than water4 #bd4 ,the ,meaning of ,heavy and ,light--,specific ,gravity4 ,we are in the habit of using the words heavy and light rather carelessly4 ,we call things that are easily lifted light1 and things that are hard to lift heavy4 ,we say that sand1 which is blown about by the wind1 is light1 and that a block of wood is heavy1 and yet we have just seen that sand is heavier1 bulk for bulk1 than wood4 ,in order to get rid of this double meaning1 the weight of a volume of any liquid or solid1 in proportion to the weight of the same volume of water at a known temperature and pressure1 is called its specific gravity4 ,water being taken as #a1 anything a volume of which is twice as heavy as the same volume of water is said to have the specific gravity #b2 if three times1 #c2 if four and a half times1 #de1 and so on4 ,thus the specific gravity of any liquid or solid expresses its density in proportion to that of water under the same conditions4 ,sawdust1 oil1 and spirit have a less specific gravity than water1 while treacle1 sand1 and quicksilver have a greater specific gravity4 ,in this sense1 the former three substances are light1 while the latter three are heavy4 #be4 ,things of greater ,specific ,gravity than ,water sink in ,water2 ,things of less ,specific ,gravity float4 ,here are two tumblers of water4 ,throw some sand into one and some sawdust into the other4 ,what happens8 ,the sand sinks to the bottom1 the sawdust floats at the top4 ,we may stir them up as we like1 but the sand will tumble to the bottom and the sawdust1 as obstinately1 rise to the top4 ,thus that which is lighter than the water floats1 and that which is heavier 7bulk for bulk7 sinks4 ,so1 if we pour some oil into the water1 it floats1 and if we pour some coloured spirit in carefully1 it also floats2 while treacle and quicksilver sink to the bottom1 just as the iron-filings do4 ,we saw that the iron-filings sank1 because iron is heavier than water4 ,here is a piece of the thin tinned sheet-iron that they make tin boxes of4 ,what will happen if we drop it into the water8 ,it is heavier than water1 bulk for bulk1 and therefore it will sink as you see it does4 ,but now here is a 8tin0 canister made of this very same tinned sheet-iron4 ,we drop that into the water1 and you see it does not sink at all1 but floats at the top as if it were made of cork4 ,here is a perplexity4 ,we were sure just now that iron is heavier than water1 and here is an iron box floating6 ,is this an exception to the law8 ,not at all2 for what we said was that a thing would float if it were lighter1 bulk for bulk1 than water4 ,now let us weigh the tin box1 and having weighed it let us next try to find out how much the same bulk of water weighs4 ,this may be done very simply1 for the walls of the box are very thin1 so that the inside of the box is very nearly as large as the whole box4 ,consequently1 if we fill the box with water1 and then weigh the water1 we shall find out1 very nearly1 what is the weight of a bulk of water as great as that of the box4 ,but if we do this1 we shall find that the water which was contained in the box1 weighs very much more than the box does4 ,so that1 bulk for bulk1 the box1 although it is made of iron1 is really lighter than water1 and that is why it floats4 ,you will all have heard of the iron ships which are now so common1 and you may have wondered how it is1 that ships made of thick plates of iron riveted together1 and weighing many thousand tons1 do not go to the bottom4 ,but they are nothing but our tin canisters on a great scale1 and they float because each ship weighs less than a quantity of water of the same bulk does4 ,it is because of this property of water to bear up things lighter than itself1 and because of that other property of being easily moved which the particles of water have1 that the sea1 and rivers1 and canals1 are such great highways for mankind4 ,for there is nothing so heavy that it may not be made to float in water1 if the box which holds it is large enough to make the weight of the whole less than the weight of the same bulk of water4 ,and then1 having once got the weight to float1 the particles of water are so easily moved1 that the force of the winds1 or of oars1 or of paddles1 readily causes it to slip through the water from one place to another4 #bf4 ,a ,body which ,floats in ,water always occupies as much ,space beneath the level of the ,surface of the ,water as is equal to the ,volume of ,water which weighs as much as that ,body2 in other words1 it displaces its own ,weight of ,water4 ,a cubic inch of water weighs about #beb grains and a half4 ,suppose that the tin box in the previous experiment was square1 and had the bulk of #ajj cubic inches1 then the weight of a corresponding volume of water would be #be1bej grains4 ,if the box weighed #h1daf grains1 just a third of its bulk would be immersed2 if #ab1fbe grains1 half2 if #af1hcb grains1 it would sink two-thirds of its volume1 and so on4 ,or1 if1 when the box is floating1 you make a mark upon its side at the exact level of the surface of the water1 the bulk of that portion of the box which lies below the water-level can be ascertained4 ,suppose it to be thirty cubic inches1 then the weight of the box will be #cj #bebe or #gege grains4 ,hence it may be said that the immersed part of a floating body takes the place of the water which it displaces1 and1 as it were1 represents it4 ,if you press downwards upon the floating box1 there is a feeling of resistance as it descends1 and when the pressure is taken off1 the body immediately rises again4 ,hence the water presses upwards against the bottom of the floating body4 ,but it also presses against the sides1 for if the sides of the box are very thin they will be driven in4 ,if a thin empty bottle is tightly corked and lowered into deep water the cork will be driven in1 or else the bottle will be crushed4 #bg4 ,water presses in all ,directions4 ,thus water presses in all directions upon things which are immersed in it4 ,if a long wooden or metal pipe1 placed vertically1 has its lower end stopped with a cork which does not fit very tightly1 and water is poured into the top of the tube1 the water will at first fill the part of the tube above the cork1 and its weight will exert a certain pressure on the cork4 ,in fact1 if the end of the tube is stopped by applying the palm of the hand closely against it1 the downward pressure of the water will have to be overcome by a certain amount of effort4 ,as the water accumulates1 this downward pressure will become greater and greater until the hand is driven away1 or the cork is forced out1 and the water falls to the ground4 ,the pressure in this case is the same as the weight of the water1 and the cork would have been driven out equally well by a rod of lead of the same weight4 ,suppose the tube to be square1 and that the inside of the square measures exactly one inch each way4 ,then an inch of height of the tube will hold exactly one cubic inch of water4 ,since one cubic inch of water weighs #beb grains and a half1 as much water as will fill the tube about two feet three inches and a half high1 will weigh a pound 7#g1jjj grains71 and fifteen pounds of water will fill such a tube between thirty-three and thirty-four feet high4 ,and these respective weights measure the pressure of two columns of water1 one twenty-seven and a half inches high1 and the other nearly thirty-four feet high1 on a square inch of the surface on which they rest4 ,the specific gravity 7 #bd7 of lead is #aade2 in other words it is about eleven and a half times denser than water4 ,therefore if a bar of lead cut square and one inch in the side1 and rather less than #a_/aath of the height of a column of water1 is slipped into the tube in place of the water1 it will exert the same pressure on the bottom4 ,and now comes a difference between the lead and the water1 which depends on the fluidity of the latter4 ,the lead exerts no pressure on the sides of the tube1 but the water does4 ,if a small hole is cut in the side of the tube close to the bottom1 and stopped with a cork1 the lead will not press upon the cork4 ,but if the column of water is high enough the cork will be driven out with as much force as before1 so that the water presses just as much sideways as downwards4 ,it is easy to satisfy oneself of this by inserting a long glass tube1 with its lower end bent at right angles and fitted with a cork1 into the side of the wooden pipe4 ,the water will at once rise in the tube to the same height as it has in the pipe4 ,whence it is obvious that the pressure of the water on any point of the side is exactly equal to the vertical pressure at that point2 for the pressure outwards is exactly balanced by that of the vertical column in the tube inwards4 ,the water in a watering-pot always stands at the same level in the can and in the spout4 ,if a glass tube is bent into the shape of a ,u1 and water is poured into it1 the water will always stand at the same level in the two legs of the tube1 whatever the shape of the bend may be1 or the relative capacities of the two legs1 or the inclination of the tube4 ,and this must needs be so1 for the force with which the water tends to flow out of the one half of the arrangement depends on the vertical height#b of the surface of the water above the aperture of exit2 so that any column of equal vertical height must balance it4 ,footnote #b3 ,vertical height is the height measured along a line drawn from the surface of the water perpendicularly to the surface of the earth4 ,a plumb-line is a string to one end of which a weight is attached and thus hangs suspended4 ,if the other end of the line is brought opposite the surface of the water the direction of the string answers to the line of vertical height4 ,that a column of water will stand at exactly the same level as any other with which it communicates1 may be seen still more simply by placing a glass tube1 open at each end1 in a basin of water4 ,however the tube may be inclined or bent1 whether its lower end is wide or narrow1 the column of water inside it will be at exactly the same level as the water outside it4 ,yet1 of course1 the rigid glass walls of the tube cut off all communication between the column of water inside it and the rest1 except at the bottom4 ,in a well-ordered town1 water is supplied to every house and can be drawn from taps placed in the highest stories4 ,these are fed by pipes which lead from a cistern at the top of the house4 ,this water is brought from a large pipe1 or main1 in the street1 by a smaller house-pipe1 which is often made to twist about in various directions before it reaches the cistern at the top of the house into which it delivers the water4 ,if you followed the main1 you would find that it took a long course up and down1 beneath the pavement of the streets1 until at last it reached the water-works4 ,here you would find that the main was connected with a reservoir2 and either this reservoir is at a greater height than any of the cisterns into which the water is delivered1 or there is some means of pumping the water from it to that height on its way to the main4 ,thus the reservoir1 the main1 and the house-pipe form one immense ,u-tube1 and the water in the house-pipe tends to rise to the same level as that of the water in the reservoir1 and hence flows into the cistern when the supply-pipe is open4 #bh4 ,the ,transference of ,motion by ,moving ,water3 the ,momentum of ,moving ,water4 ,suppose a wooden vat with a horizontal tap1 the sectional area#c of the tube of which is one square inch1 inserted close to the bottom1 to be filled with water up to #ajj inches above the tap4 ,then supposing the tap to be shut1 the pressure upon its sectional area will be #be1bej grains1 or rather more than three pounds and a half--and there is the same pressure on every square inch of the bottom of the vat4 ,footnote #c3 ,the sectional area of a tube is the surface occupied by its cavity when it is cut across4 ,it would be represented by the surface of a piece of cardboard1 like the wad of a gun1 just large enough to go into the tube4 ,if the tap is now turned1 the water nearest to it being unsupported on its outer side1 the pressure on the inner side sets it in motion1 and it flows out in a stream4 ,at first the stream shoots out violently and the water is carried to a long distance4 ,that is to say1 the weight of the column of water #ajj inches high acts as a force1 or cause of motion1 upon the water nearest the tap1 and this water is forced out with a velocity depending on that force in a horizontal direction4 ,now suppose that you take a common toy cup-and-ball and bring the ball into the way of the stream of water4 ,the stream will at once strike the ball and drive it in the same direction as that which it is itself taking4 ,the power which the moving water has of transferring or communicating motion to a body which is at rest1 but free to move as the ball is1 is due to its momentum4 ,the greater the mass of the stream and the more rapidly it moves1 the more motion will it communicate to the ball1 or the heavier the ball it will move4 ,close to the mouth of the tap the direction of the stream is horizontal2 but it very soon begins to bend downwards1 and describing a rapid curve1 comes to the ground4 ,it does this for just the same reasons that a stone thrown horizontally describes a curve2 and at length strikes the ground2 and1 in fact1 the stream may be regarded as so much water thrown horizontally4 ,these reasons are two3 firstly1 as soon as the water has left the tap it is an unsupported heavy body2 and1 as such1 it begins to fall to the ground4 ,secondly1 the momentum of the water is continually being diminished by the resistance of the air through which it passes4 ,for1 although the air which surrounds us is so thin and movable a body that we ordinarily take no notice of it--the fact that it offers resistance to bodies which move through it is easily observed2 as1 for example1 in using a fan4 ,the water has to overcome this resistance1 and its momentum is proportionally diminished4 ,if1 when the water leaves the tap1 the air and gravitation were alike abolished1 the water1 keeping its momentum1 would travel for ever in the same direction4 ,as the water runs out1 it will be observed that the velocity of the stream becomes less and the curve which it describes sharper1 so that it comes to the ground sooner2 and finally1 when the vat is nearly empty1 the stream falls nearly vertically downwards4 ,the reason of this is that the level of the top of the water is gradually lowered2 consequently1 the height of the column which presses on the water close to the tap is gradually lessened1 and therefore its weight is diminished4 ,but this weight or pressure is the cause of the motion of the water1 and as the cause diminishes the effect of that cause must diminish4 ,therefore the momentum of the water is gradually lessened and it is carried less and less far horizontally in the time which it takes to fall to the ground3 until finally1 it acquires no appreciable horizontal motion at all1 and so falls vertically downwards from the mouth of the tap4 #bi4 ,the ,energy of ,moving ,water4 ,if a short pipe bent at right angles like the letter ,l is fitted by one arm on to the end of the tap1 while the other is turned vertically upwards1 and the vat is full as before2 when the tap is turned1 the water will shoot up into the air1 and after rising for a certain distance will stop1 and then fall4 ,in fact we shall have a fountain4 ,observe the difference between the vertical jet of water and the horizontal jet4 ,if we leave the resistance of the air out of consideration1 the water in the horizontal jet has no obstacle to overcome2 and it might go on for ever1 if its weight did not gradually cause its path to become more and more bent towards the earth1 against which it eventually strikes4 ,when the jet is vertical the case is altered4 ,the water thrown up vertically constantly tends to fall down vertically1 as any other heavy body would do1 and its momentum has to overcome the obstacle of its gravity4 ,any given portion of the water is1 in fact1 acted upon by two opposite tendencies1 momentum urging it up1 and gravity pulling it down4 ,now if two equal tendencies exactly oppose one another1 the body upon which they act does not move at all2 while1 if one is stronger than the other1 the body moves in the direction of the stronger4 ,thus a portion of water which has just left the spout shoots up1 because the velocity with which it is impelled upwards is sufficient to carry it through a greater space in a given time1 say a second1 than that through which its gravity would1 in the same time1 impel it downwards4 ,but the distance which the water will travel during this second will be the difference between the distance which it would have ascended if there had been no gravity forcing it down1 and the distance which it would have descended if there had been no momentum driving it up2 and1 at the end of the second1 the rate of its motion upwards1 or its velocity1 will be proportionally slower4 ,thus1 at the end of the first second1 the water has spent a certain portion of its momentum in overcoming its gravity4 ,and as there is nothing to make good the loss1 it would1 if left to itself1 travel more slowly1 or over a less distance1 in the second second than it tended to do in the first4 ,but though the momentum of the water is diminished1 its gravity1 weight1 or tendency to fall downwards1 for a given distance in a second1 remains exactly what it was1 and operates in the course of the second second to exactly the same extent as in the first4 ,hence1 at the end of the second second1 the distance through which the water travels upwards is still smaller1 and its velocity is still more diminished4 ,it is obvious that1 however great the disproportion between momentum and gravity to start with1 gravity must gain the day in the long run under these circumstances4 ,the store of momentum will be used up2 and1 after a momentary rest1 the water1 reduced to the condition of a body without support1 will begin to be carried downwards by the unopposed action of gravity4 ,the case is similar to that of a boy sculling a boat1 the bows of which are suddenly seized and the boat thrust violently backwards by a strong man4 ,the boat will go stern-foremost rapidly1 at first1 but every stroke of the boy's oar at the stern will retard its backward motion2 until1 at length1 the stock of momentum conferred upon it by the man's thrust will be completely exhausted in working against the boy1 and the boat1 after a momentary rest1 will resume its onward course4 ,the distance to which the boat will be propelled backwards will evidently depend upon the amount of muscular power which the man1 as it were1 suddenly capitalizes in the boat1 and which the boat then slowly pays out4 ,we call people who possess much muscular or other power energetic2 and we estimate their energy by the obstacles they overcome1 or1 in other words1 by the work they do4 ,in the present illustration the man's energy would be measured by the distance to which the boat was propelled before it stopped4 ,it is easy to transfer this conception of energy1 as the power of doing work1 to inanimate things2 and thus when a body in motion overcomes any kind of obstacles in its way1 parting with its momentum and more or less coming to rest in the process1 we say that it has energy and that it does work4 ,the energy of moving water is thus measured by the intensity of the opposing forces which it can overcome multiplied into the distance which it can travel before that energy is exhausted2 that is to say1 by the work it does before it is itself reduced to a state of rest4 ,in the case under consideration1 the energy by which gravity is overcome1 for a greater or less time1 depends upon the velocity of the stream2 and this again depends upon the height of the water in the vat above the tap4 ,just as the energy of the horizontal stream diminished as the level of the water became lower1 so does the energy of the vertical stream diminish4 ,hence1 as the vat empties1 the jet becomes shorter and shorter1 until at last it sinks down to nothing4 ,the energy of moving water makes it1 under some circumstances1 one of the most destructive of natural agents2 and1 under others1 one of the most useful servants of man4 ,a stream is water falling down hill with a velocity depending upon the inclination of its bed4 ,as it falls it acquires momentum and1 hence1 energy2 and thus a mountain stream1 suddenly swollen by rain or melting snow1 will tear away masses of rock and sweep everything before it4 ,nothing can look softer or more harmless than a calm sea1 but if the wind sweeping over its surface puts the water in motion1 it strikes upon the shore with terrific force2 and its energy is expended in throwing up great waves1 which lift vast blocks or drive masses of shingle up the beach4 ,in all kinds of watermills it is the energy of more or less rapidly falling water which is turned to account4 ,the water is made to flow against buckets or floats attached to the circumference of a wheel4 ,each bucket or float is therefore an obstacle to which the water transfers some of its own motion2 it moves away and thus makes the wheel to which it is fastened turn4 ,but the turning of the wheel brings a new obstacle in the way of the stream4 ,this is treated in the same fashion1 and the wheel turns still further1 thus introducing another obstacle in the way of the stream upon which the same effect is produced4 ,thus each float1 or bucket1 is a means by which some of the momentum of the stream is1 as it were1 caught and transferred to the water-wheel1 which consequently turns round with a certain velocity4 ,but this water-wheel is now a mass of matter in motion1 and therefore itself contains a store of energy or power doing work4 ,if a cord with a weight at the end of it were fastened to the axle of the wheel1 the cord would be wound upon the axle1 and the weight could be raised1 or1 in other words1 so much work would be done by the turning of the wheel and we should thus have a rough measure of the amount of energy which had been given up by the stream to the wheel4 ,the machinery of the mill is simply a set of contrivances for transferring the energy stored up in the water-wheel to the place in which work has to be done4 ,in a flour-mill1 for example1 a series of wheels carries it from the water-wheel to the grindstones1 which it sets in motion4 #cj4 ,the ,properties of ,water are ,constant4 ,if1 whenever there is a shower1 you catch some rain-water1 you will find that it possesses all the properties which have been described4 ,it will be found to be an almost incompressible liquid1 an imperial pint of which weighs about a pound and a quarter4 ,it would make no difference if the rain-water were collected in ,africa or in ,new ,zealand2 or if it had been obtained centuries ago and kept bottled up ever since4 ,and there is every reason to believe that rain-water will have exactly the same properties a hundred or a thousand years hence4 ,so far as the properties of rain-water are concerned the order of nature is constant4 ,this1 however1 is by no means the same thing as saying that the properties of water are always the same4 ,in fact the properties of the substance1 water1 vary immensely according to the conditions to which it is exposed2 but1 under the same conditions1 they are the same1 so that we may still say that so far as water is concerned1 the order of nature is constant4 #ca4 ,increase of ,heat at first causes ,water to ,increase in ,volume4 ,it has been seen that a certain weight of water always has the same volume under the same conditions4 ,the most important of these conditions is the heat or cold to which it is exposed4 ,water which has stood for some time in a warm room becomes less in volume1 or contracts1 if it is taken into a cool place2 while its volume increases1 or it expands1 if it is made hot4 ,the same thing is true of quicksilver1 of spirit1 and of liquids in general4 ,a thermometer is simply a small flask--the bulb--with a long and narrow neck--the tube--filled with as much mercury or spirit as will rise a short distance into the neck4 ,if the liquid in the bulb is warmed1 its volume is increased and it overflows into the tube1 increasing the height of the column of liquid in the tube4 ,if1 on the other hand1 the liquid in the bulb is cooled1 its volume is diminished2 and1 as it shrinks1 the column of liquid in the tube flows back into the bulb1 and the level of the top of the column is lowered4 ,if a mark is made on the tube1 or on a scale fixed to it1 at the point which the liquid reaches when the bulb is placed in boiling water2 and another mark at the point to which it sinks when the bulb is in melting ice2 and the space between the two marks is divided into #ahj equal parts1 each of these parts is what is called a 8degree0 in the thermometers ordinarily used in this country 7called ,fahrenheit74 ,and if the boiling-point is counted as #bab the freezing-point must be #cb 7#bab - #cb #ahj74 ,with the same amount of heat the fluid in the tube always stands at the same degree1 and hence the instrument measures temperature4 ,that hot water is lighter than cold is easily seen when a bath is filled from two taps1 one of hot and one of cold water1 which run at the same time4 ,unless care is taken to stir the water1 the top of the bath will be very much hotter than the bottom4 ,thus1 an imperial pint of water weighs a pound and a quarter only at a certain temperature or degree of warmth1 namely at #fb2 if it is made hotter its volume increases1 and therefore its specific gravity diminishes4 ,it was for this reason that in #bb the weight of the same volume of water was said to be constant under the same conditions2 and1 of course1 the same qualification must be borne in mind when we speak of the weight of a cubic inch of water being about #beb and a half grains4 ,its weight is in fact #bebde grains only when ,fahrenheit's thermometer stands at #fb--;but as this is the temperature of ordinary mild weather1 and the expansion or contraction of water for a degree about this temperature amounts to less than #a_/cjjjth of its volume1 the weight of a cubic inch may for all practical purposes be taken as #beb and a half grains4 #cb4 ,increase of ,heat at length causes ,water to become ,steam4 ,thus a change is effected in the properties of water by heating it ever so little4 ,if it is more strongly heated a still greater change takes place4 ,you know what happens when a saucepan containing water is put on the fire4 ,the water gets hotter and hotter1 then it begins to simmer1 and finally1 when it reaches #bab1 it boils away into steam1 which passes into the air and disappears4 ,if the boiling is carried on long enough all the water vanishes4 ,it looks at first as if the water had been destroyed by the heat4 ,in reality1 however1 not a particle of water has been destroyed4 ,it has merely changed its state4 ,the heat has altered it from the state of liquid water into that of gaseous water1 vapour or steam4 ,try the same experiment with a tea-kettle instead of a saucepan1 but only put a little water in the tea-kettle1 and shut the lid well down4 ,then1 as soon as the water begins to boil1 the steam will shoot out of the spout in a jet2 and this will go on as long as any water remains in the kettle4 ,the steam1 as it comes out of the spout1 is so hot that it will scald you if you put your finger in it4 ,but you may satisfy yourself that it is very hot1 without scalding your fingers1 by holding a stick of sealing-wax in it4 ,the wax will soften1 just as if you held it before the fire4 ,moreover1 if you look through the steam1 just where it leaves the spout1 you will see that it is quite transparent2 it is only at some little distance from the spout that it loses its transparency1 changes into a white opaque cloud1 and rapidly vanishes in the air4 #cc4 ,the taking away of ,heat from ,steam causes the steam to change into ,hot ,water4 ,now take a cold spoon1 or a cold plate1 and hold it against the jet of steam1 for a moment or two4 ,when you take it away1 you will find that it is quite wet1 being covered with drops of warm water1 and1 moreover1 the cold spoon1 or plate1 has become warm4 ,and if you fit a long cold metal pipe to the nozzle of the tea-kettle1 you will find that no steam at all issues from the end of the pipe1 but only water1 while the pipe becomes warmed4 ,thus the heat passes from the fire into the saucepan1 or kettle1 and thence to the water which they contain2 the water gets hotter and hotter1 and1 when it has taken in a certain quantity of heat1 it becomes steam1 or vapour of water4 ,when the steam comes against the cold plate1 or passes through the cold pipe1 it gives up the heat it has taken in to the plate1 or the metal of the pipe4 ,they carry off the heat which kept the water in a condition of a vapour1 and so it passes back into the condition of liquid4 ,thus steam and water are two conditions of the same thing1 water2 they are effects of the quantity of heat which the water has taken in4 #cd4 ,when ,water is changed into ,steam1 its ,volume becomes about #a1gjj times greater that it was at first4 ,if you could measure and weigh the water in your kettle to begin with1 and then measure and weigh all the steam into which the heat of the fire changes it1 you would find that the bulk of the steam was nearly #a1gjj times as great as the bulk of the water1 though the weight of the steam would be exactly the same as that of the water4 ,if you had a small square cup like a die1 the inside measure of which was exactly one inch each way1 it would hold one cubic inch of water4 ,if this cup full of water were heated till all the water was turned into steam1 the steam would nearly occupy a cubic foot2 since there are #a1gbh cubic inches in a cubic foot4 ,a cubic inch of water weighs #beb grains1 and the steam into which it is converted has just the same weight4 ,thus we may say that steam is water expanded by heat into a vapour which is of #a1gjj times less specific gravity than water4 ,on the other hand1 a pint of steam allowed to cool1 becomes converted into a quantity of water1 which measures only #a_/agjjth of a pint1 though it weighs just as much as the whole pint of steam did4 ,the steam1 therefore1 is condensed to a #a_/agjjth of its volume of water4 ,the power with which water expands when it is converted into steam is very great4 ,if you were to stop up the nozzle of the tea-kettle1 the steam1 inside the kettle1 in trying to expand1 would burst open the lid2 and if you were to fasten down the lid1 it would pretty soon burst the kettle itself4 ,you sometimes hear of the strong boilers of steam-engines being burst in this way4 #ce4 ,gases or ,elastic ,fluids4 ,air4 ,here is a glass flask with a long neck and an open mouth4 ,if we pour water in at the mouth until it rises to the lip we say that the flask is full of water4 ,if we now pour the water out we say that the flask is empty4 ,but is it empty8 ,press the flask mouth downwards into a glass jar full of water4 ,if the flask were empty there would be no reason why the water should not enter the neck of the flask and stand at the same height inside the neck as it does outside4 ,if you take an 8empty0 glass tube open at each end and press it down into the water1 the water inside and the water outside will stand at the same level4 ,but if you put your finger on the upper end of the tube so as to convert it into a closed vessel1 the water will enter the lower end only a little way4 ,so with the flask1 the water enters the neck only a little way4 ,hence there is something inside the 8empty0 tube and in the 8empty0 flask2 something which is material1 because it occupies space and offers resistance4 ,in fact the flask is full of that form of matter which is termed air1 a thick coat of which surrounds the earth as the atmosphere4 ,air has weight1 as you will learn more fully by and by2 and that air in motion can transfer that motion to other bodies you are taught by the effects of the winds1 which are merely air in motion4 ,air therefore has all the characters of a material substance4 ,moreover it is a fluid1 for it fits itself exactly to the shape of any vessel which contains it2 its parts are very easily moved1 or we should feel its resistance every time we move a limb2 that it 8flows0 is seen in every breeze and every time you use a pair of bellows1 when the air is driven in a stream out of the nozzle2 and it presses on all sides anything contained in it4 ,but though air is a fluid it is not a liquid4 ,in the first place it is very compressible4 ,we saw that the water entered a little way into the tube or the neck of the flask in the preceding experiment4 ,the reason of this is that the water compresses the air into a smaller volume4 ,a bag full of air1 such as a common air-cushion1 can be squeezed till the air in its interior occupies a much smaller volume2 and1 if you treat a syringe full of air in the same way as the syringe full of water was treated1 you will find1 if the piston fits well1 that it can be driven down some distance and then springs back again4 ,air in fact is not only a compressible1 but it is an elastic fluid or gas4 ,heat expands air just as it expands water1 but the expansion of air for the same degree of heat is much greater4 #cf4 ,steam is an ,elastic ,fluid or ,gas4 ,in all the properties which have been mentioned water in the form of steam is an elastic fluid or gas like air4 ,if a little water is placed in the flask mentioned in the preceding section all the 8empty0 part of the space will contain air4 ,if the flask is now made hot the water will at length boil1 bubbles of steam forming in the water and breaking at its surface4 ,by degrees1 the air1 which at first lay above the water1 will be driven out2 and if the whole flask is kept hot1 the 8empty0 part of it will be full of the gaseous water1 which is transparent and colourless like air4 ,the steam flows out of the mouth of the flask still a clear and colourless gas2 but it soon cools and becomes condensed as a cloud of small particles of fluid water4 ,steam is lighter than air1 and hence it rises in the air1 just as bodies which are lighter than water rise in water4 #cg4 ,gases and ,vapours4 ,air is as much a gas in the coldest winter as it is in the hottest summer4 ,but air can be liquefied by exposing it to a very low temperature1 while1 at the same time1 it is subjected to an extremely great pressure4 ,thus1 the difference between gases like air1 which are condensed with extreme difficulty1 and gases like steam1 which are condensed easily1 is only one of degree4 ,nevertheless there is a certain convenience in distinguishing those gases1 which1 like steam1 are easily condensed as vapours4 ,in what we ordinarily call steam1 all the water of which it is composed remains gaseous only at and above the temperature of boiling water 7#bab ,fahrenheit74 ,cooled ever so little below this point1 most of it becomes condensed into hot liquid water4 ,however1 it must be recollected that though that particular form of gaseous water which we call steam exists only at and above the temperature of boiling water1 yet water is capable of existing in the gaseous state down to the freezing-point4 ,suppose that when our boiling flask contained nothing but water and steam1 the mouth were stopped and the lamp removed4 ,then1 so long as the temperature of the whole remained at that of boiling water1 every cubic inch of steam above the water in the flask would weigh about th of a grain1 since #ajj cubic inches weigh about #ae grains4 ,suppose the capacity of the flask1 exclusively of the fluid water in it1 to be #ajj cubic inches4 ,then1 to begin with1 the gaseous water which it contains will weigh #ae grains4 ,if the flask is now allowed to cool1 more and more of the gaseous water condenses into the fluid state2 but1 even down to the freezing-point1 some water will remain in the gaseous state and will fill that part of the flask which is unoccupied by the fluid water4 ,at blood-heat 7#ih7 the gaseous water weighs only about a grain1 though it still occupies #ajj cubic inches2 at the ordinary temperature of the air it weighs not more than rd of a grain2 while1 at the freezing-point1 its weight is only th of a grain4 ,but inasmuch as there is less and less actual weight of water in the same volume of gaseous water as the temperature falls1 it follows that the density1 or specific gravity1 of the gaseous water must be less the lower the temperature4 ,moreover1 while1 at the boiling-point1 gaseous water or steam resists compression with exactly the same force as air does1 the lower the temperature the more easily compressible is the gaseous water4 ,suppose an elastic bag were to be tied on to the nozzle of a kettle full of boiling water4 ,if the bag were kept as hot as the boiling water it would become fully distended1 and maintain its shape in spite of the pressure of the air upon all sides of it4 ,if the bag were taken away it would retain its shape so long as it was kept as hot as boiling water2 but1 if it were allowed to cool1 it would gradually become flattened by the outside air squeezing up the less and less resisting gaseous water of the lower temperatures4 ,hence1 when the stopped flask has been allowed to cool1 the air rushes in with great violence if it is opened4 #ch4 ,the ,evaporation of ,water at ordinary ,temperatures4 ,if some water is poured into a saucer and is allowed to stand even in a cool room or in the open air1 you know that it sooner or later disappears4 ,wet clothes hung on a line soon dry--that is to say1 the water clinging to them disappears or evaporates4 ,the disappearance of the water under these circumstances results from the property just mentioned4 ,in fact1 it becomes gaseous water of the density appropriate to the temperature1 and as such mixes with the air as any other gas would do4 ,and as the sea1 lakes1 and rivers1 are constantly giving off gaseous water into the air in proportion to the temperature1 it is not wonderful that the atmosphere always contains gaseous water4 ,air is said to be moist when the weight of water in a given quantity1 say #ajj cubic inches1 is as much1 or nearly as much1 as can exist in the state of gas at the temperature4 ,under these circumstances1 if the temperature is lowered even a very little1 some of the gaseous water is converted into liquid water4 ,we see this in hot moist weather1 when the outside of a tumbler of fresh drawn cold spring water immediately becomes bedewed4 ,the gaseous water in immediate contact with the tumbler1 in fact1 is cooled down below the point at which it can all exist as gas1 and the superfluity is deposited as dew4 ,in such days wet clothes do not dry well1 because there is1 already1 nearly as much gaseous water in the atmosphere as the amount of heat marked by the thermometer can maintain in that state4 #ci4 ,when ,hot ,water is cooled1 it ,contracts to begin with1 but after a time ,expands4 ,we have now seen what a wonderful change is brought about by heating water4 ,at first1 it expands gradually and slightly2 but1 when it reaches the boiling-point1 it suddenly expands enormously1 and is no longer a liquid1 but a gas4 ,on the other hand1 if warm water is allowed to cool1 it gradually contracts till it reaches the ordinary temperature of the air in mild weather2 but1 if the weather is very cold1 or if the water is cooled artificially1 it goes on contracting only down to a certain temperature 7#ci71 and then begins to expand again4 ,in this peculiarity water is unlike all other bodies which are fluid at ordinary temperatures4 ,hence the temperature of #ci is that at which pure water has its greatest density or specific gravity1 and water at this temperature is heavier1 bulk for bulk1 than the same water at any other temperature4 ,therefore if water at the top of a vessel is cooled down to this temperature1 it falls to the bottom1 and if the water at the bottom of a vessel is cooled below this temperature it rises to the top4 #dj4 ,water cooled still further becomes the transparent brittle solid ,ice4 ,our tumbler of water1 if put out of doors on a cold winter's night1 would gradually cool until it assumed a temperature of #ci throughout4 ,cooling below this temperature1 the water so cooled would gradually accumulate at the surface by reason of its less density1 and its temperature would fall till the thermometer placed in it marked #cb4 ,as soon as this upper water cooled ever so little below #cb1 a film like glass would form on its surface by the conversion of the coldest fluid water into solid water or ice4 ,and if all the water cooled down to the same degree it would all gradually change into the same kind of substance4 ,in this condition water is solid4 ,it occupies space1 offers resistance1 has weight and transmits motion as the water did1 but if you shake it out of the tumbler in a cold place it retains its form without the least change4 ,if you press it1 it proves to be exceedingly hard and unyielding2 and1 if the pressure is increased1 it becomes crushed and breaks like glass4 ,it may thus be crushed to powder1 and the ice powder can be formed into heaps as if it were sand4 ,just as any quantity of steam has exactly the same weight as the water which was converted into it by heat2 so the ice has exactly the same weight as the water which has been converted into it by taking away heat4 #da4 ,ice has less ,specific ,gravity than the ,water from which it was formed4 ,but though the ice in the tumbler has the same weight as the water had1 it has not the same volume4 ,the expansion which began at #ci goes on1 and when water passes into the solid state its volume is about #a_/aath greater than it was at #ci4 ,taking water at this temperature as #aj1 ice has a specific gravity of #jiaf4 ,but although water in freezing expands only to this small amount1 it resembles steam in the tremendous force with which it expands4 ,if you fill a hollow iron shell quite full of water1 screw down the opening tight1 and then put it in a cold place where the water may freeze1 the water as it freezes will burst the iron walls of the shell4 ,you know that when the winter is severe1 the pipes by which water is brought to a house often burst4 ,this is because the water in them freezes1 and1 being unable to get out of the pipe1 bursts it1 just as you may burst a jacket that is too tight for you by stretching yourself4 ,among the bare hill-tops1 or on the face of cliffs exposed to the weather1 the strongest and hardest rocks are every winter split and broken1 just as if quarrymen had been at work at them4 ,in the summer the rain-water gets into the little cracks and rifts in the stone and lodges there4 ,then the winter comes with its cold and freezes the water4 ,and the water bursts the rocks asunder just as it bursts our waterpipes4 #db4 ,hoar ,frost is the ,gaseous ,water which exists in the ,atmosphere1 condensed and converted into ,ice ,crystals4 ,in the winter-time you often notice1 on a clear sharp night1 that the tops of the houses and the trees are covered with a white powder called hoar frost2 and1 on the windows of the room when you wake up1 you see most beautiful figures1 like delicate plants4 ,take a little of the hoar-frost1 or scrape off some of the stuff that makes the window look like ground glass1 and you find that it melts in your hand and turns to water4 ,it is in fact ice4 ,and if you look at the figures on the window pane with a magnifying glass you will see that they are made up bits of ice which have a definite shape1 and are arranged in a regular pattern4 ,each of these definitely shaped bits of ice has been formed in the following way4 ,the air in the room is much warmer than that outside1 and there is mixed with it nearly as much water1 derived from the breath and the evaporation of moist surfaces1 as can maintain itself in the gaseous state at the temperature4 ,the windowpanes1 being thin1 are cooled by the outside air1 and of course the gaseous water inside the room1 when it comes in contact with the cold windowpanes1 becomes condensed on them into fine drops of cold water4 ,the panes becoming colder and colder1 these minute drops at last freeze1 and the water not only becomes solid1 but it crystallises2 that is to say1 the little solid masses take on more or less regular geometrical forms with flat faces1 inclined to one another at constant angles1 so that they resemble bits of glass cut according to particular fixed patterns4 ,all ice is in fact crystalline1 but in ice which has been formed from thick sheets of water1 the crystals are so packed together that they cannot be distinguished separately4 #dc4 ,when ,ice is warmed it begins to change back into ,water as soon as the ,temperature reaches #cb4 ,a lump of ice brought out of the open air in very cold weather may have a temperature of #cj1 or #bj1 or lower4 ,if such a lump is brought into a warm room it gradually becomes warmer1 but remains unchanged otherwise1 until it has risen to #cb4 ,then it begins to melt1 and remains at #cb as long as it is melting2 and the water which proceeds from it is at first also at #cb4 ,if you were to throw a lump of ice into the middle of a hot fire1 so long as a particle of ice remained as such1 it would have a temperature of #cb and no more4 ,this is a fact exactly parallel to that which is observed when water is raised to the boiling-point4 ,so long as any of the water remains unconverted into steam it becomes no hotter4 ,moreover the steam itself is at first at #bab4 #dd4 ,ice the solid1 ,water the liquid1 and ,steam the gas1 are three states of one natural object2 the ,condition of each ,state being a certain ,amount of ,heat4 ,ice1 liquid water1 and steam1 are three things as unlike as any three things can well be4 ,what do we mean then by saying that they are states of one substance1 water8 ,what we really mean is that if we take a given quantity of water1 say a cubic inch1 and change it first into ice and then into steam1 there is something which remains identically the same through all these changes4 ,this something is1 in the first place1 the weight of the material substance4 ,the water weighs #beb grains1 the ice into which it is converted weighs #beb grains1 and the steam produced from it weighs #beb grains4 ,in the second place1 the same force would cause the ice1 the water1 and the steam1 to move with the same rapidity2 and1 when set in motion1 they would produce the same effect upon anything movable against which they struck4 ,in the third place1 when you study chemistry1 you will learn that the ice1 the steam1 and the liquid water1 would yield the same weight of the same two gases1 oxygen and hydrogen1 and nothing else4 ,every one cubic inch of water1 #a1gjj cubic inches of steam1 and #a_/aaa cubic inch of ice1 yield #bha_/ah grains of hydrogen1 with #bbdh_/ah grains of oxygen1 and nothing else4 7,see #ej47 ,as there is not the slightest difference in weight between a given quantity of water and the ice1 or the steam1 into which it may be converted1 it is clear that the heat which is added to or taken from the water to give rise to these several states1 can possess no weight4 ,if then heat is a material body1 it must be devoid of weight--and hence1 in former times1 heat was called an imponderable substance4 ,it was thought to be a kind of fluid1 called caloric1 which had no weight1 and which drove the particles of bodies asunder1 when it entered them as they were heated1 and let them come together as it left and they grew cool4 #de4 ,the ,phenomena of ,heat are the ,effects of a rapid ,motion of the ,particles of ,matter4 ,this much1 however1 is certain3 that heat can be caused by motion4 ,every boy knows that a metal button may be made quite hot by rubbing it4 ,a skilful smith will hammer a piece of iron red hot4 ,the axles of wheels become red hot by rubbing against their bearings1 if they are not properly lubricated2 and even two pieces of ice may be melted by the heat evolved when they are rubbed together4 ,and there are abundant other reasons1 as you will find when you study physics1 for the belief that the sensation we call heat1 and all the phenomena which we ascribe to heat1 are the effects of the rapid motion of matter4 ,however1 a quiescent body may be made hot without exhibiting the least appearance of motion4 ,the surface of the water in a tumbler at #ajj is just as unruffled as that of the same water at #cb4 ,what1 then1 is meant by saying that heat is a kind of motion1 and that the greater the heat in any body the greater the amount of motion in that body8 ,the answer to this question is that the motion which causes the phenomena of heat1 is not a visible motion of the whole mass of the hot body1 but a motion of the individual particles of which it is composed4 ,and each particle moves1 not straight forward1 but backwards and forwards in the same space1 so that its motion may be roughly compared to that of a pendulum1 or to that of the balance-wheel of a watch4 ,it is in fact a sort of vibratory movement2 each vibration taking place through a very short distance and with extreme rapidity4 ,the sensation of heat is caused by the vibratory movements of the particles of matter1 just as sound is so caused4 ,the prongs of a tuning-fork which has been struck1 certainly vibrate1 for you can see them do so if the note is low4 ,if you now put your ear at one end of a long piece of timber and the handle of the vibrating tuning-fork is placed upon the other end1 the vibratory motion of the tuning-fork will be communicated to the particles of the wood and will be loudly heard4 ,all the time the sound is heard the particles of the wood are vibrating4 ,nevertheless1 the wood as a whole does not move1 but its particles swing backwards and forwards through such a minute space that their motion is imperceptible4 ,but what are these particles of matter which by their vibration give rise to the phenomena of heat8 #df4 ,the ,structure of ,water4 ,we have seen that pure water is perfectly clear and transparent4 ,the naked eye can discern no difference between one part and another4 ,in other words1 it has no visible texture or structure4 ,it does not follow that it really possesses none1 however1 for there are many things which seem to be the same throughout1 or homogeneous1 which yet show structure if they are examined with a magnifying glass4 ,thus the surface of a sheet of fine white paper looks perfectly even and smooth to the eye2 but a magnifying glass of no great power will show the minute woody fibres of which it is made up2 while1 under a powerful microscope1 the paper looks like a coarse matting4 ,but if we put a small drop of water on a slide1 such as is used for microscopic objects1 and cover it over with a thin glass so as to spread it out into a film1 perhaps not more than #a_/ajjjjth of an inch thick1 it may be examined with the very highest magnifying powers we can command1 and yet it looks as completely homogeneous and shows as little evidence of being made up of separate parts as before4 ,however1 this is still no proof that the water is not made up of little parts1 or particles1 distinctly separated from one another4 ,it may merely mean that the particles are so extremely small that they cannot be distinguished even by microscopes which magnify four or five thousand diameters4 ,it is certain that solid bodies may be divided into particles so minute that the best microscopes show no trace of them4 ,common gum-mastic cannot be dissolved by water1 but it readily dissolves in strong spirit or alcohol1 and mastic varnish is an alcoholic solution of gum-mastic4 ,if you add water to mastic varnish1 the alcohol takes away the water and the mastic falls out1 or precipitates1 as a curdy solid composed of very visible whitish particles4 ,but if a drop of the varnish is added to a good deal1 say half a pint1 of water and well stirred at the same time1 the mastic1 though it is still precipitated as a solid1 is in a state of extremely minute division4 ,no separate solid particles of mastic are visible to the naked eye1 but the water assumes a faint milky tinge4 ,this milkiness arises from the presence of solid particles of mastic diffused through the water2 and yet1 if the experiment has been properly managed1 a drop of the fluid may be spread out as before and examined with the highest magnifying powers1 and nothing can be seen of such particles4 ,so far as vision goes it might be a drop of pure water4 ,now our best microscopes are able to show us anything solid which has a diameter of #a_/ajjjjjth of an inch1 quite distinctly2 and probably solid opaque particles of much smaller size would make themselves apparent as a turbidity or cloudiness4 ,the particles of mastic must be therefore so much smaller than this that they remain invisible4 ,hence it follows that if water were made up of separate particles1 or droplets1 #a_/ajjjjjjth of an inch in diameter1 and thus had the structure of a mass of very fine shot1 no microscope that has yet been constructed would enable us to see even a trace of that structure4 ,we could not obtain any direct evidence of it4 #dg4 ,suppositions or ,hypotheses2 their ,uses and their ,value4 ,when our means of observation of any natural fact fail to carry us beyond a certain point1 it is perfectly legitimate1 and often extremely useful1 to make a supposition as to what we should see1 if we could carry direct observation a step further4 ,a supposition of this kind is what is called a hypothesis1 and the value of any hypothesis depends upon the extent to which reasoning upon the assumption that it is true1 enables us to explain or account for the phenomena with which it is concerned4 ,thus1 if a person is standing close behind you1 and you suddenly feel a blow on your back1 you have no direct evidence of the cause of the blow2 and if you two were alone1 you could not possibly obtain any2 but you immediately suppose that this person has struck you4 ,now that is a hypothesis1 and it is a legitimate hypothesis1 first1 because it explains the fact2 and1 secondly1 because no other explanation is probable2 probable meaning in accordance with the ordinary course of nature4 ,if your companion declared that you fancied you felt a blow1 or that some invisible spirit struck you1 you would probably decline to accept his explanation of the fact4 ,you would say that both the hypotheses by which he professed to explain the phenomenon were extremely improbable2 or in other words1 that in the ordinary course of nature fancies of this kind do not occur1 nor spirits strike blows4 ,in fact1 his hypotheses would be illegitimate1 and yours would be legitimate2 and1 in all probability1 you would act upon your own4 ,in daily life1 nine-tenths of our actions are based upon suppositions or hypotheses1 and our success or failure in practical affairs depends upon the legitimacy of these hypotheses4 ,you believe a man on the hypothesis that he is always truthful2 you give him pecuniary credit on the hypothesis that he is solvent4 ,thus1 everybody invents1 and1 indeed1 is compelled to invent1 hypotheses in order to account for phenomena of the cause of which he has no direct evidence2 and they are just as legitimate and necessary in science as in common life4 ,only the scientific reasoner must be careful to remember that which is sometimes forgotten in daily life1 that a hypothesis must be regarded as a means and not as an end2 that we may cherish it so long as it helps us to explain the order of nature2 but that we are bound to throw it away without hesitation as soon as it is shown to be inconsistent with any part of that order4 #dh4 ,the ,hypothesis that ,water is composed of ,separate ,particles 7,molecules74 ,it has been pointed out that we cannot see1 and indeed that there is not much hope of our ever being able to see1 the separate particles of water1 even if water is composed of such particles4 ,but it is perfectly legitimate to suppose that water is made up of such particles1 if that hypothesis will enable us to explain the properties of water4 ,let us suppose then that any portion of fluid water is really composed of a prodigious number of particles less 7and probably much less7 than a millionth of an inch in diameter4 ,we may call these particles molecules4#d ,footnote #d3 ,diminutive of moles1 a mass4 ,we are justified1 in accordance with the general properties of matter 7 #ah71 in supposing that these molecules tend to approach one another4 ,but the fact that water is slightly compressible justifies the supposition that its molecules are not in actual contact1 but that they are separated by interspaces1 just as the motes in the air of a dusty room are so separated4 ,what is it that keeps the molecules apart8 ,we have seen that great mechanical pressure brings them but slightly nearer to one another2 hence there is an equivalent resistance of some kind which keeps them apart4 ,this resistance must have the same origin as the sensation which we know as heat1 for it has been seen that diminution of heat diminishes the bulk of water2 that is1 allows the molecules to come closer together2 that is1 diminishes their tendency to keep asunder4 ,increase of heat1 on the other hand1 increases the volume of water2 that is to say1 drives the molecules further apart1 or increases their tendency to keep asunder4 ,suppose we call the cause of the tendency of the molecules of water to come together an attractive force2 and the cause of their keeping apart1 which manifests itself to us as the sensation of heat and is1 as we have seen1 in all probability1 a rapid vibratory or whirling motion of the molecules1 a repulsive force2 then1 in the liquid state1 these forces are so adjusted that the molecules are quite free to move1 and yet hold together4 ,by adding heat the repulsive force is increased1 until the molecules are about twelve times as far apart as they were in each direction2 while the attractive force is overcome1 and the molecules fly off in all directions as soon as they are unconfined4 ,on the other hand1 by taking heat away1 the repulsive force is diminished1 until the molecules become inseparable and the water assumes the solid form4 ,it is probable that the expansion of fluid water1 at a temperature below #ci1 depends upon the molecules taking up a peculiar arrangement as they approach one another4 ,if sixteen men are formed into a column1 four deep1 and each man a foot from the other1 the same men may stand closer together and yet form a hollow square1 which occupies a larger space4 ,that the molecules of water do take up a particular order in assuming the solid condition1 is shown by the crystalline form of ice4 ,each crystal of hoar-frost owes its shape to the arrangement of its molecules1 according to a definite geometrical pattern4 ,thus the hypothesis that water is composed of separate molecules1 is useful1 for it helps us to some extent to explain the properties of water4 ,and1 when you study physics and learn the laws of motion1 you will find that there is no end to the number of the truths established by observation and experiment1 which can be explained by this hypothesis4 ,hence it may fairly be adopted and employed as a means of picturing to ourselves the order of nature1 so long as no facts are discovered which are inconsistent with it4 #di4 ,all ,matter is probably made up either of ,molecules or of ,atoms4 ,the same reasons which lead to the adoption of the hypothesis that water is composed of separate particles justify its extension to all forms of matter whatever4 ,the metal mercury or quicksilver1 for instance1 may be supposed to be made up of distinct particles of mercury of extreme minuteness1 and according to the temperature1 these associate themselves in the solid 7frozen mercury71 liquid 7ordinary quicksilver71 or gaseous form 7vapour of mercury74 ,to whatever treatment pure mercury may be subjected1 we cannot get anything but mercury out of it4 ,the particles of mercury have never been broken up4 ,hence they are generally termed atoms1 or particles that cannot be divided2 and mercury is said to be an element1 or a substance which is not compounded of any other substances4 ,here is a case in which it is very useful to distinguish between fact and hypothesis4 ,the matter of fact is that1 up to the present time1 no one has been able to get out of pure mercury anything but pure mercury4 ,the statement that mercury is a simple substance1 and therefore never can be broken up into any other substances1 is a hypothesis which future observation and experiment may or may not confirm4 ,a hundred and fifty years ago it was universally believed that water was as much an element as mercury4 ,but water is now well known to be a compound4 ,in fact1 as has already been said1 the particles of water may be very readily broken up or decomposed 7in what way1 you will learn when you study chemistry7 into two totally distinct substances1 oxygen and hydrogen1 which are gaseous at all known temperatures1 though by combining vast pressure with extreme cold they have recently been liquefied4 ,each of these gases1 according to our hypothesis1 consists of particles1 and since these can by no known means be further broken up1 they are considered to be atoms like those of mercury4 ,nine parts by weight of pure water always yield eight of oxygen and one of hydrogen4 ,the hypothetical particle1 or molecule of water1 therefore1 must be composed of atoms of oxygen and hydrogen having this relative weight2 and chemists have grounds for believing that one atom of oxygen and two atoms of hydrogen exist in each molecule of water4 ,if this be so1 the structure of water must be more complicated than we thought at first2 and each particle of water 7the molecule7 must be a system composed of three separate atoms4 #ej4 ,elementary ,bodies are neither destroyed nor is their ,quantity increased in ,nature4 ,it has been seen that when a cubic inch of water is dissipated by heat1 it is not destroyed1 but that it merely changes its form from the fluid to the gaseous state1 while its weight remains unaltered4 ,if the same cubic inch of water is decomposed into oxygen and hydrogen gases1 the water is indeed destroyed1 but the matter of which it consisted remains unchanged in weight4 ,if the water weighed #bebe grains1 the oxygen gas will weigh #bbdde grains and the hydrogen gas will weigh #bhje grains4 ,and nothing that man has been able to do has affected the weight of a given quantity of either of these gases4 ,so far as we know1 elementary bodies retain their weight under all circumstances1 and can be traced by it whatever shape they may take4 ,if this is true it follows that1 in the order of nature1 matter is indestructible3 the quantity of it neither increases nor diminishes4 ,hence it follows that natural things and artificial things resemble one another in one respect4 ,it is true of both that the matter of which they are composed is never destroyed and never increased2 and therefore the order of events in nature as much consists in the joining together and putting apart of natural bodies by natural agencies1 as the order of events in the artificial world consists in the joining together and the putting apart of natural bodies by human agencies4 #ea4 ,simple ,mixture4 ,in order to learn the manner in which water may be broken up into its elements or decomposed1 you must turn to the ,primer on ,chemistry4 ,but as a preliminary to the study of that science1 it may be useful to consider some simple cases of composition and decomposition which are exemplified by water4 ,if half a pint of water1 coloured by putting a little ink into it1 is added to the same quantity of clean water1 the two will readily mingle2 the total quantity of water will be a pint2 and its colour will be just half as dark as that of the coloured half-pint4 ,this is a case of simple mixture4 ,the volume of the mixture equals the sum of the volumes of the things mixed1 and there is no change in the properties of these things4 ,so when water evaporates1 the gaseous water or vapour mixes with the air in the same way1 the molecules of the one body dispersing themselves between the molecules of the other until there is the same proportion of each everywhere4 ,in like manner1 sand and sugar may be 7and unfortunately often are7 mixed1 without any change in the properties of either1 or in the space which they primitively occupied4 ,on the other hand1 oil and water will not mix1 however much you may stir the two together2 and the oil1 being the lighter1 rises to the top as soon as the fluid is quiet4 ,nor will quicksilver and water mix1 but the quicksilver1 being very much heavier than the water1 rushes to the bottom of the vessel into which the two are put4 ,neither will sand nor iron filings mix with water2 as heavier bodies1 they also sink to the bottom4 ,nor does powdered ice1 though it is water in another shape1 mix with ice cold water2 as a lighter body it floats at the top4 #eb4 ,mixture followed by ,increase of ,density2 ,alcohol and ,water4 ,strong spirit1 or alcohol1 is a clear transparent fluid which looks like water1 but is a very different substance4 ,for example1 it boils at a much lower temperature1 it burns with a blue flame1 it has intoxicating properties1 and1 like oil1 it is very much lighter than water4 ,hence1 if coloured spirit is poured gently upon the surface of water the spirit rests upon the water4 ,suppose1 now1 that we take a tall measure graduated into ten equal parts4 ,fill the lower five with water1 and then1 very gently1 pour in the strongest alcohol1 coloured in some way1 until the tenth mark is reached4 ,we shall have five volumes of water below1 and an equal quantity1 or five volumes1 of coloured alcohol above4 ,where the two are in contact1 the colour will be diffused into the water for a short distance1 but not far1 showing that only a slight mixture is taking place4 ,this1 however1 is not because the two fluids mingle with difficulty2 for1 with slight stirring1 they mix completely1 and you have a fluid the colour of which is about half as intense as that of the alcohol1 and many of the other properties of which are intermediate between those of pure alcohol and those of pure water4 ,thus far1 nothing further than simple mixture1 as when coloured water was added to pure water1 seems to have occurred2 but1 in reality1 something more has happened4 ,in the first place1 the mixture is a good deal warmer than either of its components2 that is to say1 heat has been generated4 ,in the second place1 if you measure the volume of the whole fluid after it has cooled1 it no longer stands at the mark ten1 but distinctly lower1 or about nine and three-quarters4 ,as the volume of the mixture is less than the sum of the volumes of its two components1 it follows that the density of the mixture must be greater than a density midway between that of the water and that of the alcohol4 ,in other words1 the molecules in the mixture do not occupy the same space as they did when they were separate4 ,the result is the same as if the ten volumes had been compressed until they occupied only nine and three-quarters2 so that the effect is a contraction similar to that which would be brought about by taking away heat from the mixture4 ,in fact1 as we have seen1 the mixture gives out a quantity of heat4 ,there is another respect in which the mixture is unlike both its constituents4 ,it both boils and freezes at a much lower temperature than water does1 and at a higher temperature than alcohol does4 ,in fact pure alcohol has not yet been frozen4 ,if the molecules of the alcohol were merely diffused among those of the water as water is diffused through wet sand1 they ought to pass into the gaseous state at the same temperature as that at which alcohol boils2 and it would then be very easy to separate alcohol from water by distillation4 ,but the fact is not so2 alcohol cannot be obtained free from water by distillation unless something which holds water very strongly1 such as quicklime1 is added1 so as to keep all the water back when the fluid is heated4 ,thus alcohol and water1 mingled together1 give rise to a fluid which is not a mere mixture1 the properties of which are known if we know the properties of its components2 it is1 in strictness1 a new body1 in which the molecules of the water and those of the alcohol affect one another to a certain extent and modify the pre-existing properties of each4 ,this effect of different bodies upon one another becomes much more manifest when water is brought into contact with certain solids4 #ec4 ,solution2 ,water ,dissolves ,salt4 ,if a spoonful of salt is put into a tumbler of cold water and the water is stirred1 the salt swiftly vanishes from view2 and1 after a time1 so far as our sense of vision goes1 the water appears to be just what it was before4 ,but if the water in the tumbler at first weighed five ounces and the salt weighed two ounces1 the water in the tumbler will now weigh seven ounces2 the water will now taste salt1 the salt is said to be dissolved1 and the solution is called brine4 ,moreover1 the solution is said to be saturated1 for if you put more salt in it will remain unchanged4 ,water1 in fact1 will dissolve two-fifths of its weight of salt and no more4 ,if the brine thus formed is put into a wide dish1 so that the water may evaporate2 or if it is heated and the water boiled away2 as fast as the water diminishes1 a quantity of salt1 equal to two-fifths of the water which is converted into steam1 returns to the solid state and falls to the bottom of the vessel4 ,and when all the water is driven off1 the salt which remains will have exactly the weight1 and all the other properties which it had before it was dissolved by the water4 ,thus1 contact with water has had a very singular effect upon the salt4 ,it appears to have changed one of the properties of the salt1 namely1 its solidity1 but to have left all the rest unaltered4 ,we saw just now that powdered ice does not mix with ice-cold water1 but that the fragments of ice remain solid4 ,the moment1 however1 that the temperature rises1 the cohesion1 or sticking together of the molecules1 which is the characteristic of the solid state1 comes to an end2 they become loose and free to move1 and they mingle with the surrounding water4 ,or we may say that the ties which held the molecules of the solid together are dissolved1 so that the solid water becomes fluid4 ,the resemblance of this process to the dissolving of salt in water is so obvious that1 in common language1 it is often said that a lump of salt or of sugar melts away in water2 but if you try to make salt fluid by heat1 you will have to expose it to a very high temperature1 so that the conversion of salt from the solid state into the liquid state by solution in cold water is obviously a very different process from liquefaction by heat4 ,nevertheless the result is the same so far as the condition of the salt is concerned4 ,the cohesion between its molecules is destroyed1 and they distribute themselves evenly among the molecules of the water1 just as the molecules of steam distribute themselves among the molecules of air4 ,and1 when you study chemistry1 you will learn how it may be proved that the smallest drop of the solution of salt contains exactly the same proportion of salt as the whole does4 ,if brine is allowed to evaporate slowly1 the molecules of the salt arrange themselves1 as the water leaves them1 in beautifully regular cubical crystals4 ,you may see them form easily enough if you watch a drop of brine gradually dry up under a microscope4 ,the salt crystals contain nothing but salt4 ,if they are heated till they become red-hot they pass into the fluid state2 and when still further heated1 the fluid salt becomes a vapour or gas and1 as such1 flies off into the air1 or volatilizes4 ,thus we see that when salt and water are brought into contact1 the salt undergoes a certain amount of change1 while the water does not remain wholly unchanged4 ,for brine no longer boils at #bab1 but requires a considerably higher temperature4 ,the salt1 as it were1 holds the water back1 and prevents it from assuming the gaseous state under the same conditions as if it were pure1 just as1 in the previous case1 the water held the alcohol back2 or we may say that the force of heat which drives the molecules of liquid water apart1 when steam is formed1 has a greater resistance to overcome when salt is dissolved in the water4 ,and just as the presence of alcohol lowers the freezing point of the water with which it is mixed1 so does the presence of salt lower the freezing point of water4 ,sea water1 which is a weak brine1 begins to freeze at about #bg2 and the ice which is formed is quite pure1 while the remainder of the sea water becomes richer in salt4 ,if we mean by attraction that which opposes any force which tends to separate bodies1 then we may say that the molecules of salt and those of water attract one another4 ,and such attraction between molecules of matter of different kinds is called chemical attraction4 #ed4 ,quicklime and ,water3 ,plaster of ,paris and ,water3 ,combination4 ,quicklime is a substance obtained by heating chalk or limestone to redness4 ,when pure1 it is a white hard solid which can be made to pass into the liquid and gaseous states only at enormously high temperatures4 ,if a lump of fresh quicklime be placed in a saucer and about one-third of its weight of water poured upon it1 there will be a great turmoil1 heat will be evolved1 the water will disappear1 and the lime will crumble down into a soft white powder4 ,this operation is what bricklayers call slaking lime4 ,and if no more water has been added than the proportion mentioned1 the pure white powder which results will be solid and dry1 the water having1 to all appearance1 vanished4 ,in the solution of salt we saw a solid become fluid under the influence of water2 in the slaking of lime the fluid water enters into the structure of a solid4 ,if more water is added1 this solid dissolves or becomes liquid1 as the salt did1 and the solution is called limewater4 ,by carefully managed evaporation of the water the lime may be recovered in the form of crystals1 just as the salt was recovered4 ,but there is this difference1 that the salt crystals contain no water1 while the lime crystals not only contain water1 but contain exactly the same proportion as exists in slaked lime1 that is to say1 #ah parts water to #ef parts lime4 ,the water thus bound up with the lime into a new solid holds on so firmly to the lime that it requires a red heat to separate the two4 ,the lime and the water are said to be chemically combined2 and as the proportion of lime and water in slaked lime1 or lime crystals1 is always the same1 they are said to be combined in definite proportions2 and the slaked lime receives the special name of hydrate of lime4 ,gypsum or ,plaster of ,paris is a dry white powder4 ,if mixed with a little water it does not slake after the fashion of quick lime1 but the mixture soon sets or becomes hard2 and1 at the same time1 the greater part of the water disappears4 ,in fact1 it has combined with the plaster of ,paris and forms part of another hydrate1 in which1 when the superfluous moisture dries1 not a trace of water is to be seen4 ,it is this property which is taken advantage of when plaster of ,paris is used in making casts and moulds4 ,the fluid plaster is poured over and round the body to be cast2 as a fluid1 it applies itself conveniently to all the inequalities of its surface2 and1 when it sets1 it retains the shape which it has thus acquired4 ,set plaster of ,paris may be perfectly dry2 but it nevertheless contains between and of its weight of water1 fixed and forming an integral part of the solid hydrate4 ,and if the set plaster is strongly heated1 the combined water is driven off and it returns to its original state4 ,gypsum is found abundantly in nature1 in the shape of beautiful transparent crystals which are called selenite4 ,these crystals have the same composition as set plaster1 that is to say1 they are hydrates4 ,a thin flake of such a crystal viewed with the highest powers of the microscope appears perfectly homogeneous4 ,nevertheless1 there is good reason for the conclusion that it consists of molecules of water and molecules of gypsum which hold together so strongly that they form a hard brittle glassy solid4 ,moreover1 the molecules of the hydrate itself hold together more strongly in some directions than in others4 ,it is very easy to split the crystals lengthwise2 while much more force is needed to cut them crosswise and then they do not split1 but break4 ,glauber's salts and ,epsom salts are other examples of solids which dissolve in water and separate in the crystalline form as the water evaporates2 and which1 like lime and gypsum1 combine with a definite proportion of water to form crystalline compounds4 ,in fact1 each of these glassy brittle solids contains more than half its weight of water4 ,thus we see that two bodies1 of which water is one1 may combine together to give rise to something different from either4 ,and we are thus led to the science of chemistry1 which tells us exactly how bodies combine1 what comes of their combination1 and how compounds may be separated into their constituents4 #ee4 ,mineral bodies may take on definite shapes and grow1 or increase in size1 by the addition of like parts4 ,water and all the other natural bodies which have hitherto been mentioned1 are what are called mineral bodies1 although1 in common use1 the term mineral is usually restricted to ores and metals4 ,now we have repeatedly had occasion to remark that1 under certain circumstances1 not only water1 but many other mineral bodies1 assume regular shapes4 ,the most familiar example is that of the beautiful imitation of leaves and foliage which is presented by the ice which forms on a window in winter4 ,but we have also seen that common salt1 lime1 gypsum1 ,glauber's salts and ,epsom salts1 also assume the crystalline form as they or their compounds with water are deposited from their solutions4 ,and if a drop of solution of ,glauber's salts or of ,saltpetre1 is allowed to evaporate under the microscope1 a wonderful spectacle will be presented4 ,as the salt assumes the solid state1 the crystals suddenly appear in the field of view as needles and plates disposed in beautiful patterns1 which rival those of hoar frost1 though they are quite different from them4 ,in fact1 as you will learn if you study crystallography1 every crystallizable substance has its proper crystalline forms and never departs from certain strictly related geometrical figures4 ,a crystal of any of these substances will grow if placed under proper conditions4 ,thus1 if a crystal of common salt is hung by a thread in a saturated solution of salt1 which is exposed to the air1 so as to allow the water to evaporate slowly1 the molecules of the salt which is left behind and can no longer be held in solution1 deposit themselves on the crystal in regular order and increase its size without changing its form4 ,and1 in this way1 the small crystal may grow to a great size4 ,the large crystals of sugar candy1 which consist of sugar and water deposited from a strong syrup or saturated solution of sugar1 grow in the same fashion1 upon threads suspended in the evaporating syrup4 ,in this mode of growth you will observe that the enlargement is effected by addition to the outside of the growing body2 and moreover the matter which is added1 namely1 the salt or the sugar1 already exists as salt in the brine or as sugar in the syrup4 ,b4 ,,living ,,bodies4 #ef4 ,the ,wheat ,plant and the substances of which it is composed4 ,every one has seen a cornfield4 ,if you pluck up one of the innumerable wheat plants which are fixed in the soil of the field1 about harvest time1 you will find that it consists of a stem which ends in a root at one end and an ear at the other1 and that blades or leaves are attached to the sides of the stem4 ,the ear contains a multitude of oval grains which are the seeds of the wheat plant4 ,you know that when these seeds are cleared from the husk or bran in which they are enveloped1 they are ground into fine powder in mills1 and that this powder is the flour of which bread is made4 ,if a handful of flour mixed with a little cold water is tied up in a coarse cloth bag1 and the bag is then put in a large vessel of water and well kneaded with the hands1 it will become pasty1 while the water will become white4 ,if this water is poured away into another vessel1 and the kneading process continued with some fresh water1 the same thing will happen4 ,but if the operation is repeated the paste will become more and more sticky1 while the water will be rendered less and less white1 and at last will remain colourless4 ,the sticky substance which is thus obtained by itself is called gluten2 in commerce it is the substance known as maccaroni4 ,if the water in which the flour has thus been washed is allowed to stand for a few hours1 a white sediment will be found at the bottom of the vessel1 while the fluid above will be clear and may be poured off4 ,this white sediment consists of minute grains of starch1 each of which1 examined with the microscope1 will be found to have a concentrically laminated structure4 ,if the fluid from which the starch was deposited is now boiled it will become turbid1 just as white of egg diluted with water does when it is boiled1 and eventually a whitish lumpy substance will collect at the bottom of the vessel4 ,this substance is called vegetable albumin4 ,besides the albumin1 the gluten1 and the starch1 other substances1 about which this rough method of analysis gives us no information1 are contained in the wheat grain4 ,for example1 there is woody matter or cellulose1 and a certain quantity of sugar and fat4 ,it would be possible to obtain a substance similar to albumin1 starch1 saccharine and fatty matters1 and cellulose1 by treating the stem1 leaves1 and root in a similar fashion1 but the cellulose would be in far larger proportion4 ,straw1 in fact1 which consists of the dry stem and leaves of the wheat plant1 is almost wholly made up of cellulose4 ,besides this1 however1 it contains a certain proportion of mineral bodies1 among them1 pure flint or silica2 and1 if you should ever see a wheat rick burnt1 you will find more or less of this silica1 in a glassy condition1 in the embers4 ,in the living plant1 all these bodies are combined with a large proportion of water1 or are dissolved1 or suspended in that fluid4 ,the relative quantity of water is much greater in the stem and leaves than in the seed4 #eg4 ,the ,common ,fowl and the ,substances of which it is ,composed4 ,everybody has seen a common fowl4 ,it is an active creature which runs about and sometimes flies4 ,it has a body covered with feathers1 provided with two wings and two legs1 and ending at one end in a neck terminated by a head with a beak1 between the two parts of which the mouth is placed4 ,the hen lays eggs1 each of which is enclosed in a hard shell4 ,if you break an egg the contents flow out and are seen to consist of the colourless glairy 8white0 and the yellow 8yolk40 ,if the white is collected by itself in water and then heated it becomes turbid1 forming a white solid1 very similar to the vegetable albumin1 which is called animal albumin4 ,if the yolk is beaten up with water1 no starch nor cellulose is obtained from it1 but there will be plenty of fatty and some saccharine matter1 besides substances more or less similar to albumin and gluten4 ,the feathers of the fowl are chiefly composed of horn2 if they are stripped off and the body is boiled for a long time1 the water will be found to contain a quantity of gelatin1 which sets into a jelly as it cools2 and the body will fall to pieces1 the bones and the flesh separating from one another4 ,the bones consist almost entirely of a substance which yields gelatin when it is boiled in water1 impregnated with a large quantity of salts of lime1 just as the wood of the wheat stem is impregnated with silica4 ,the flesh1 on the other hand1 will contain albumin1 and some other substances which are very similar to albumin1 termed fibrin and syntonin4 ,in the living bird1 all these bodies are united with a great quantity of water1 or dissolved1 or suspended in water2 and it must be remembered that there are sundry other constituents of the fowl's body and of the egg1 which are left unmentioned1 as of no present importance4 #eh4 ,certain ,constituents of the ,body are very similar in the ,wheat ,plant and in the ,fowl4 ,the wheat plant contains neither horn1 nor gelatin1 and the fowl contains neither starch1 nor cellulose2 but the albumin of the plant is very similar to that of the animal1 and the fibrin and syntonin of the animal are bodies closely allied to both albumin and gluten4 ,that there is a close likeness between all these bodies is obvious from the fact that when any of them is strongly heated1 or allowed to putrefy1 it gives off the same sort of disagreeable smell2 and careful chemical analysis has shown that they are1 in fact1 all composed of the elements ,carbon1 ,hydrogen1 ,oxygen1 and ,nitrogen1 combined in very nearly the same proportions4 ,indeed1 charcoal1 which is impure carbon1 might be obtained by strongly heating either a handful of corn1 or a piece of fowl's flesh1 in a vessel from which the air is excluded so as to keep the corn or the flesh from burning4 ,and if the vessel were a still1 so that the products of this destructive distillation1 as it is called1 could be condensed and collected1 we should find water and ammonia1 in some shape or other1 in the receiver4 ,now ammonia is a compound of the elementary bodies1 nitrogen and hydrogen2 therefore 7 #ej7 both nitrogen and hydrogen must have been contained in the bodies from which it is derived4 ,it is certain1 then1 that very similar nitrogenous compounds form a large part of the bodies of both the wheat plant and the fowl1 and these bodies are called proteids4 #ei4 ,proteid ,substances are met with in ,nature only in ,animals and ,plants2 and ,animals and ,plants always contain ,proteids4 ,it is a very remarkable fact that not only are such substances as albumin1 gluten1 fibrin and syntonin1 known exclusively as products of animal and vegetable bodies2 but that every animal and every plant1 at all periods of its existence1 contains one or other of them1 though1 in other respects1 the composition of living bodies may vary indefinitely4 ,thus1 some plants contain neither starch nor cellulose1 while these substances are found in some animals2 while many animals contain no horny matter and no gelatin-yielding substance4 ,so that the matter which appears to be the essential foundation of both the animal and the plant is the proteid united with water2 though it is probable that1 in all animals and plants1 these are associated with more or less fatty and amyloid 7or starchy and saccharine7 substances1 and with very small quantities of certain mineral bodies1 of which the most important appear to be phosphorus1 iron1 lime1 and potash4 ,thus there is a substance composed of water proteids fat amyloids mineral matters which is found in all animals and plants2 and1 when these are alive1 this substance is termed protoplasm4 #fj4 ,what is meant by the word ,living8 ,the wheat plant in the field is said to be a living thing2 the fowl running about the farm-yard is also said to be a living thing4 ,if the plant is plucked up1 and if the fowl is knocked on the head1 they soon die and become dead things4 ,both the fowl and the wheat plant1 as we have seen1 are composed of the same elements as those which enter into the composition of mineral matter1 though united into compounds which do not exist in the mineral world4 ,why then do we distinguish this matter when it takes the shape of a wheat plant1 or a fowl1 as living matter8 #fa4 ,the ,living ,plant increases in size1 by adding to the ,substances which compose its ,body1 like ,substances2 these1 however1 are not derived from without1 but are manufactured within the ,body of the ,plant from simpler ,materials4 ,in the spring1 a wheat-field is covered with small green plants4 ,these grow taller and taller until they attain many times the size which they had when they first appeared2 and they produce the heads of flowers which eventually change into ears of corn4 ,in so far as this is a process of growth1 accompanied by the assumption of a definite form1 it might be compared with the growth of a crystal of salt in brine3 but1 on closer examination1 it turns out to be something very different4 ,for the crystal of salt grows by taking to itself the salt contained in the brine1 which is added to its exterior2 whereas the plant grows by addition to its interior3 and there is not a trace of the characteristic compounds of the plant's body1 albumin1 gluten1 starch1 or cellulose1 or fat1 in the soil1 or in the water1 or in the air4 ,yet the plant creates nothing 7 #ej7 and1 therefore1 the matter of the proteids and amyloids and fats which it contains must be supplied to it1 and simply manufactured1 or combined in new fashions1 in the body of the plant4 ,it is easy to see1 in a general way1 what the raw materials are which the plant works up1 for the plant gets nothing but the materials supplied to it by the atmosphere and by the soil4 ,the atmosphere contains oxygen and nitrogen1 a little carbonic acid gas1 a minute quantity of ammoniacal salts1 and a variable proportion of water4 ,the soil contains clay and sand 7silica71 lime1 iron1 potash1 phosphorus1 sulphur1 ammoniacal salts1 and other matters which are of no importance4 ,thus1 between them1 the soil and the atmosphere contain all the elementary bodies which we find in the plant3 but the plant has to separate them and join them together afresh4 ,moreover1 the new matter1 by the addition of which the plant grows1 is not applied to its outer surface1 but is manufactured in its interior2 and the new molecules are diffused among the old ones4 #fb4 ,the ,living ,plant1 after it has grown up1 detaches part of its ,substance1 which has the ,power of developing into a similar ,plant1 as a ,seed4 ,the grain of wheat is a part of the flower of the wheat plant1 which1 when it becomes ripe1 is easily separated4 ,it contains a minute and rudimentary plant2 and1 when it is sown1 this gradually grows1 or becomes developed into1 the perfect plant1 with its stem1 roots1 leaves and flowers1 which again give rise to similar seeds4 ,no mineral body runs through a regular series of changes of form and size and then gives off parts of its substance which take the same course4 ,mineral bodies present no such development and give off no seeds or germs4 ,they do not reproduce their kind4 #fc4 ,the ,living ,animal increases in ,size by adding to the ,substances which compose its ,body1 like ,substances2 these1 however1 are chiefly derived directly from other ,animals or from ,plants4 ,the fowl in the farm-yard is incessantly pecking about and swallowing now a grain of corn1 and now a fly or a worm4 ,in fact1 it is feeding1 and1 as every one knows1 would soon die if not supplied with food4 ,it is also a matter of every day knowledge that it would not be of much use to give a fowl the soil of a cornfield1 with plenty of air and water1 to eat4 ,in this respect1 the fowl is like all other animals2 it cannot manufacture the proteid materials of its body1 but it has to take them ready made1 or in a condition which requires but very slight modification1 by devouring the bodies either of other animals or of plants4 ,the animal or vegetable substances devoured are taken into the animal's stomach2 they are there digested or dissolved2 and thus they are fitted to be distributed to all parts of the fowl's own body1 and applied to its maintenance and growth4 #fd4 ,the ,living ,animal1 after it has grown up1 detaches part of its ,substance1 which has the ,power of growing into a similar ,animal1 as an ,egg4 ,the fowl's egg is formed in the body of the hen1 and is1 in fact1 part of her body inclosed in a shell and detached4 ,it contains a minute rudiment of a fowl2 and when it is kept at a proper temperature by the hen's sitting upon it1 or otherwise1 for three weeks1 this rudiment grows or develops1 at the expense of the materials contained in the yolk and the white1 into a small bird1 the chick1 which is then hatched and grows into a fowl4 ,the animal1 therefore1 is produced by the development of a germ in the same way as the plant2 and1 in this respect1 all plants and all animals agree with one another and differ from all mineral matter4 #fe4 ,living ,bodies differ from ,mineral ,bodies in their ,essential ,composition1 in the manner of their ,growth1 and in the fact that they are reproduced by ,germs4 ,thus there is a very broad distinction between mineral matter and living matter4 ,the elements of living matter are identical with those of mineral bodies2 and the fundamental laws of matter and motion apply as much to living matter as to mineral matter2 but every living body is1 as it were1 a complicated piece of mechanism which 8goes10 or lives1 only under certain conditions4 ,the germ contained in the fowl's egg requires nothing but a supply of warmth1 within certain narrow limits of temperature1 to build the molecules of the egg into the body of the chick4 ,and the process of development of the egg1 like that of the seed1 is neither more nor less mysterious than that1 in virtue of which1 the molecules of water1 when it is cooled down to the freezing-point1 build themselves up into regular crystals4 ,the further study of living bodies leads to the province of ,biology1 of which there are two great divisions--,botany1 which deals with plants1 and ,zoology1 which treats of animals4 ,each of these divisions has its subdivisions--such as ,morphology1 which treats of the form1 structure1 and development of living beings1 and ,physiology1 which explains their actions or functions1 besides others4 ,,iii4 ,,immaterial ,,objects4 #ff4 ,mental ,phenomena4 ,material objects are all either not living1 that is to say1 mineral bodies1 or they are living bodies4 ,everything which occupies space1 offers resistance1 has weight and transfers motion1 belongs to one or other of these two great provinces of nature4 ,the sciences of ,astronomy1 ,mineralogy1 ,physics1 and ,chemistry deal with the former1 while ,biology1 with its two divisions of ,zoology and ,botany1 treats of the latter4 ,but natural knowledge is not exhausted by this catalogue of its topics4 ,in the very first paragraph of this ,primer1 in fact1 we had occasion to draw a distinction between ,things1 or material objects1 and ,sensations2 and a moment's reflection is sufficient to convince you that sensations are not material objects4 ,a smell takes up no space and has no weight2 and to speak of a pound or of a cubic foot of sound1 or of brightness1 is1 on the face of the matter1 an absurdity4 ,pleasure is said metaphorically to be fugitive1 but you cannot imagine a pleasure as a thing in motion4 ,what we call our ,emotions are in like manner devoid of all the characters of material bodies4 ,love and hatred1 for example1 cannot for a moment be conceived to have shape1 or weight1 or momentum4 ,and when1 in reasoning1 we think1 our ,thoughts have the same lack of the qualities of material things4 ,sensations1 emotions1 and thoughts1 thus constitute a peculiar group of natural phenomena1 which are termed mental4 #fg4 ,the order of ,mental ,phenomena3 ,psychology4 ,a definite order obtains among mental phenomena1 just as among material phenomena2 and there is no more chance1 nor any accident1 nor uncaused event1 in the one series than there is in the other4 ,moreover1 there is a connection of cause and effect between certain material phenomena and certain mental phenomena4 ,thus1 for example1 certain sensations are always produced by the influence of particular material bodies on our organs of sense4 ,the prick of a pin gives pain1 feathers feel soft1 chalk looks white1 and so on4 ,the study of mental phenomena1 of the order in which they succeed one another1 and of the relations of cause and effect which obtain between them and material phenomena1 is the province of the science of ,psychology4 ,all the phenomena of nature are either material or immaterial1 physical or mental2 and there is no science1 except such as consists in the knowledge of one or other of these groups of natural objects1 and of the relations which obtain between them4 ,,the ,,end4 ---------------------------------------- -------------------------------- ,,transcriber',s ,,notes #a4 ,silently corrected typographical errors and variations in spelling4 #b4 ,retained anachronistic1 non-standard1 and uncertain spellings as printed4 #c4 ,footnotes have been re-indexed using numbers4 #d4 ,enclosed italics font in underscores4 #e4 ,enclosed bold font in equals4