50 



POftTLAR SOiEKOE II^EWS. 



[Apuii., 1889. 



Water, in freezing, passes at once from 

 the liquid to the solid state, without any 

 intermediate condition of softness and plas- 

 ticity, as is the case with glass, iron, and 

 many other substances. One moment it is 

 water — but, in an instant, a needle-like crys- 

 tal shoots across the surface, and a portion 

 has been transformed into ice. Water, also, 

 is one of the few substances which is lighter 

 in the solid than the liquid state, and this 

 projjerty is one of the most important princi- 

 ples in Nature, for, if ice were heavier than 

 water, and sank to the bottom as fast as it 

 formed, in a few years all our lakes, ponds, 

 rivers, and probably the polar oceans 

 themselves, would become solid masses of 

 ice, which the summer's sun would be unable 

 to melt. 



If we cool water from the boiling-point 

 (212*^ F.) to the freezing-point (32°), we 

 shall set free, as it were, 180 degrees of heat. 

 Now if we continue the cooling till the water 

 is frozen, we find that the thermometer still 

 indicates the same temperature of 32°, but 

 an additional quantity of heat has been set 

 free from the water in the process of chang- 

 ing to ice, and investigators have found that 

 142 degrees of heat are thus set free ; and, 

 conversely, when the ice is melted again, the 

 same amount of heat — which is called latent 

 heat — is absorbed iu the process of liquefac- 

 tion, before the thermometer begins to show 

 any change of temperature. That is to say, 

 in order to transform a pound of ice at 32'^ 

 into a pound of water at 32", we must use as 

 much heat a? would raise a poimd of water 

 from 32*^ to 142", or much more than half- 

 way to the boiling-point. Making a more 

 practical and familiar application of these 

 figures, we find that a pound of ice can reduce 

 the temperature of three pounds of water 

 from So'' to 32*^, and we thus see how impor- 

 tant a matter this latent heat of ice becomes, 

 for, if it were not for this absorption of heat, 

 the pound of ice would only reduce the 

 three pounds of water from 80*^ to 68^. 



After ice is once formed, it follows the 

 same laws of heating and cooling as any other 

 solid. A popular magazine once stated that 

 the lower the temperature at which water 

 was frozen, the colder would be the ice. This 

 is only true in an extremely limited sense. 

 If a piece of ice formed at a temperature be- 

 low zero, is exposed to a temperature above 

 32", the temperature of the whole mass rap- 

 idly rises to 32", just as a piece of stone or 

 iron would, but at that point liquefaction and 

 the absorption of latent heat begins, and the 

 full cooling power of the ice is exerted. 

 Not until the last particle is melted will the 

 temperature rise above 32°, and all ice is 

 equally "cold," whether it is formed at a 

 temperature one or a hundred degrees below 

 the freezing-point. 



A simple experiment, to show this absorp- 



tion of latent heat, can be performed by tak- 

 iitg two glasses, one containing water mixed 

 with broken ice, and the other water cooled 

 to 32° by a piece of ice, which is removed 

 before commencing the experiment. A ther- 

 mometer immersed in each will indicate 32°. 

 Set both glasses near the stove, or in a very 

 warm place, wait till the ice in the first glass 

 is nearly melted, and then take the tempera- 

 ture again. In the glass containing water 

 only it will be found to have risen se\eral de- 

 grees ; in the one containing ice and water, it 

 will still remain at 32°. Both have received 

 the same amount of heat, but in one case it 

 has been absorbed by the ice in melting and 

 rendered latent, without raising the tempera- 

 ture of the liquid. 



From the above facts it will be seen that 

 ice alone ean never freeze anything brought 

 in contact with it. It will only reduce its 

 temperature to 32^^, and there the action 

 stops, for, as no more ice can be melted at 

 that temperature, no more heat can be ab- 

 sorbed from the body in contact with it. 

 If we force the ice to melt at a lower temper- 

 ature, by the addition of chemicals — such as 

 salt, for instance — more heat will be absorbed 

 by it, and any liquid or solid in contact with 

 it will be frozen, as is illustrated every day in 

 the preparation of ice cream. A large num- 

 ber of such "freezing mixtures," as they are 

 called, are known to chemists, some of which 

 — like nitrate of ammonia and water — do 

 not require any ice at all. 



Ice is a crystalline body, and almost invari- 

 ably crystallizes in hexagonal, or six-sided, 

 forms. It is claimed that it sometimes forms 

 crystals of the trimetric system, but the obser- 

 vation has not been confirmed. This crys- 

 talline structure is not very evident in a mass 

 of ice, unless one observes it when water first 

 commences to freeze, but it is beautifully 

 shown in a snowflake, as well as by the frost- 

 work which forms on window-panes in win- 

 ter. This law of crystallization extends 

 through nearly all inorganic forms of matter, 

 and not the tiniest snowflake falls to the 

 ground, without being shaped by the same 

 mysterious forces which have given a definite 

 structure to the rocks of entire mountain- 

 chains, or even to the solid crust of the earth 

 itself. 



[Orijjinal in The Popular Science Xews.i 

 EVOLUTION. 



BY PROFESSOR JAMES H. STOLLER. 



FIRST PAPER. 



EVOLUTION AS A PRINCIPLE. 



It is the purpose of these papers to present in un- 

 technical language an account of the doctrine of 

 evolution. While much has been written upon the 

 subject, it is still true that the facts and principles 

 which underlie the ruling doctrine of modern science 

 have not yet become a part of popular knowledge, 

 and it is too often the case that vague, confused and 

 erroneous notions, as to the nature of evolution as a 

 scientific doctrine, are entertained. Perhaps this is 



not to be wondered at, considering the comprehen- 

 siveness of the subject, and the fact that its litera- 

 ture is, for the most part, too technical to be well 

 understood by the general reader, or, so far as it has 

 been reduced to popular form, too fragmentary to 

 afford adequate information. It is therefore believed 

 that a careful review of the subject, free from tech- 

 nicalities, but not on that account less accurate and 

 scientific, will meet a need. 



It is necessary at the outset to distinguish between 

 evolution as a principle, and evolution as a doctrine 

 of science. In other words, we must understand 

 clearly the nature of evolution as a process before 

 we can understand it as a theory offered in explana- 

 tion of certain classes of facts of nature. In the 

 present paper we shall consider evolution merely in 

 the light of a process. For this purpose it is not 

 necessary to go into the realm of nature at all ; 

 abundant illustrations of the principle are at hand 

 in every department of human activity. 



If we consider the history of the class of things to 

 which any article of common use belongs, we shall 

 find that it is one of progressive development. To 

 make this clear, let us trace out the probable history 

 of some familiar article — the pocket-knife, for in- 

 stance. The story runs about as follows : Primi- 

 tive man, realizing the need of a cutting-instrument, 

 at first used sharp-edged stones, picked up from the 

 base of cliffs or bed of streams. For a long time, 

 such rude, natural tools met all his requirements — 

 enabling him, perhaps, to dig out his cave-dwelling, 

 and to hew down small trees. But, with larger 

 needs, attendant upon a gradually increasing intel- 

 ligence, the edged stone became more and more 

 unsatisfactory to him, and finally the luminous idea 

 of making a cutting-instrument, instead of finding 

 one, occurred to him. He found that by chipping 

 to an edge one fiint-stone by means of another, the 

 product of his human art was far better than the 

 mere by-play of nature's operations. Having once 

 clearly realized his power of fashioning things to 

 his needs, he was not long in learning to improve 

 his stone axe by polishing the rough chipped sur- 

 faces into smoothness. (Archx'ologists recognize an 

 age of chipped stone implements, and another of 

 polished stone implements.) The next step in ad- 

 vance was in fitting a handle to this implement, so 

 that it could be wielded with greatly increased 

 power in felling trees, and otherwise adapted to 

 greater serviceability. With instruments of stoner 

 thus perfected, our remote ancestors were content 

 fora long period. But, gradually, they found out that 

 other materials could be fashioned into edged im- 

 plements, and, especially, that by heating and fusing 

 certain substances found here and there outcropping 

 on the hillsides, a compound could be formed, capa- 

 ble of being hammered into blades. Thus were 

 formed edge-tools of bronze. (The bronze age of 

 archieology.) From these the passage was not dif- 

 ficult to edge-tools of iron. (Iron age.) Then fol- 

 lowed a rapid development, resulting in a wide 

 variety of instruments — many for the needs of war 

 and the chase, and some for the arts of peace and 

 for household use. Of the former sort — weapons 

 of attack and defence — we may imagine rude swords, 

 spears, and axes, of varying forms, sizes and quali- 

 ties of workmanship ; of the latter sort — implements 

 of agriculture and the priniitive constructive arts, 

 and of domestic use — we may picture to ourselves 

 rough spades, adzes, chisels, knives, and shears, in 

 equal variety. Finally, coming down to modern and 

 civilized times, when iron is tempered into steel, we 

 have cutting-instruments of almost endless variety, 

 and in adaptation to every kind of practical need. 

 One of these is our pocket-knife — an instrument for 

 sundry small and entirely peaceful offices, consisting 

 of a blade jointed to a handle, and capable of being 



