SCIENCE. 



change of position in space cf the centre of gravity of the 

 atom, and the other the change of form of the atom itself ; 

 the first of these is known as free path motion, and the 

 second as heat. ' The evidence for this may be briefly 

 given. 



First — It is certain that a heated body loses its heat by 

 radiation, that is. it imparts its motion to the ether which 

 transmits it in every direction as undulations having cer- 

 tain wave lengths and amplitudes. Second — It is cer- 

 tain that the energy of such undulations depends upon 

 the amplitude of such- undulations, and if the am- 

 plitude of the undulation was measured by the free path 

 of the atom, then the radiant energy of the atom would 

 vary as its free path, or in other words the rarer a gas is 

 the greater its radiant energy. Now when the spectrum 

 of a gas, say hydrogen, is examined, it is seen to be com- 

 posed of lines having definite wave lengths, and wave 

 length is dependent solely upon the rate of vibration. If 

 this rate depended upon the number of impacts per second 

 of the atoms or molecules of a gas, then these atoms would 

 need to be always at exactly the same distance apart and 

 the velocity of free path motion invariable, which condi- 

 tions are physically impossible among free atoms, other- 

 wise the spectrum we should obtain would be a continu- 

 ous spectrum such as solid incandescent bodies give. 

 But the spectrum of hydrogen for a given temperature is 

 the same whether the gas be at ordinary pressure or very 

 rare. This necessitates the conclusion that the heated 

 atom which is thus radiating energy is vibrating quite in- 

 dependent of its position in space or of its free path 

 motion, and the energy embodied in such vibratory motion 

 is often spoken of as internal energy. When a swiftly 

 moving bullet strikes a target, both bullet and target are 

 heated and oftentimes a flash of light may be seen at the 

 instant of impact. The free path motion has been 

 changed into atomic vibrations, which at the first instant 

 had a period capable of giving the sensation of light, but 

 if the bullet be picked up at once it may not be uncom- 

 fortably hot. Now imagine two atoms in space urged by 

 gravitation towards each other until they strike each 

 other ; each will be set vibrating, that is they will both 

 be heated by impact, and until they were thus made to 

 vibrate they would have no temperature at all ; their 

 energy would be represented by their free path motion ; 

 the greater their distance apart, when they began to ap- 

 proach, the greater would be their velocity at impact, and 

 the period of vibration of each after impact would de- 

 pend upon the character of the atoms themselves. One 

 might have such a period as to give out undulations that 

 might affect the eyes and we would say it was luminous 

 while the other one might not, luminosity being dependent 

 upon the rate of vibration, not upon the energy ot vibra- 

 tion or the amplitude. 



There are many phenomena, that are familiar enough, 

 which show that luminosity does not depend upon h'gh 

 temperature. The decaying stump that shines at night, 

 has a temperature not appreciably higher than surround- 

 ing objects ; the swift moving molecules in a Crookestube, 

 that spend their energy upon the walls of the tubs, cause 

 the latter to glow, and the molecules themselves shine as 

 they move in their long, free paths, but the tube is not un- 

 comfortably hot, much less very hot. It is true that by 

 increasing the energy of the moving atoms, the tube may- 

 be made red hot, but the point here is, that this is not es- 

 sential for luminosity. 



If then, in the process of universe building, we start 

 with dissociated atoms, without any temperature, — at ab- 

 solute zero, and let gravitation alone act among them, the 

 first motions will be free path motions, and there will be 

 no such thing as heat until atomic impact has begun ; the 

 energy that was at first represented solely by gravitation 

 will now be partly changed into heat and radiation proper 

 will begin, and the actual loss of energy to the involved 

 atom will be greater than what would be due solely to 

 gravitative approach ; there might be luminousness with 



very little temperature, and one might speak of it as "fire 

 mist," and as " glowing vapor," and yet not threaten the 

 " Law of Interaction of Forces." Neither does the Neb- 

 ula Theory fall, if originally matter was not hot, but cold. 



Tufts College, Mass. 



A. E. DOLBEAR. 



DISCREPANCIES IN RECENT SCIENCE. 



To the Editor of "SCIENCE:" 



In his communication to your excellent journal (Vol. 

 II., p. 142), Mr. Larkin has very correctly stated the dis- 

 crepancy which is contained in the designation "fire-mist," 

 as applied to the initiatory s'age of nebular cosmogeny, 

 the "Chaos" of Laplace — sit veniaverbo ! If the Nebular 

 Hypothesis is a true representation of ihe history of our 

 solar system for all solar and other systems, for that 

 matter) then, certainly, heat could have been present only 

 after motion, and very lively motion at that, had been 

 going on for quite a number of — well, let us say, 

 billions of years, or pretty nearly that. 



As soon as motion, i. e., aggregation (and rotation) 

 had begun, then, by the impact of the more distant por- 

 tions of matter on those nearer the centre of the solar 

 nucleus, heat was produced equivalent to the motion 

 thus arrested. The primordial " Chacs," therefore, was 

 cold and dark, if it ever did exist at all. 



Mr. Larkin, consequently, is correct : There is a dis- 

 crepancy ! 



Not so, Mr. Morris, whose objection is stated, in mice, 

 by himself (Vol. II., No. 41) in these words: 



" Temperature and heat are very different things." 



" It is one thing to contain heat and another thing to 

 be in what we call a heated state." 



To prove this he mentions the generally accepted facts 

 "that a mass of water at 32" contains far more heat than an 

 equal mass of ice at the same temperature ; and a mass of 

 water gas, (steam?) at 212 contains far more heat than 

 an equal mass ef water at that temperature." 



The foregoing facts illustrate the phenomenon of 

 " latent heat " or heat not appreciable by the thermome- 

 ter. But latent heat is not heat .' It is a misnomer that 

 should have been eradicated from scientific nomenclature 

 long ago. The heat which melts a pound of ice is em- 

 ployed in performing a certain amount of work by over- 

 coming the cohesion of the solid ice. Its subsequent 

 liquid state is the result of this work of heat. This heat 

 has disappeared, is no more heat ; exactly as the muscu- 

 lar force of the locksmith's arm disappears (is latent) at 

 night, because by eight hours of filing he has overcome the 

 cohesion of a quantity of iron. We can not look for the 

 work and the tcrce spent on it at the same time. 



The greater mobility of the liquid and the diminished 

 cohesion are the equivalent of the heat that has " become 

 latent," t. e., disappeared, absolutely, utterly and entirely, 

 as heat. In changing water back again into ice, from 

 the liquid into the solid state, the same amount of heat 

 must be liberated, withdrawn, or allowed to escape, as 

 was necessary to melt it. 



Water, therefore, does not contain more heat "than ice 

 at 32 F.; it contains more mobility, energy, potentiality 

 — in short, more motion, but not motion of the heaf kind. 



The same relations exist between water and steam at 

 212 F. Here the peculiar property of the gaseous con- 

 dition allows us to appreciate the nature of the difference 

 between water and steam much more precisely than that 

 between water and ice. "Latent heat" is here simply 

 expansion, and as expansion is the work of heat it is not 

 heat. This we can prove by confining steam or any gas 

 in a vessel with a movable wall. If the gas just fills the 

 receptacle and we now apply heat, a thermometer will 

 show a rise of temperature in the interior of the vessel. 



As soon as the heat reaches a certain point, so that the 



