32 



NATURE 



[IMav 12. 1892 



" In a few important respects Waterston stopped short. 

 There is no indication, so far as I can see, that he recog- 

 nized any other form of motion, or energy, than the 

 translatory motion, though this is sometimes spoken of as 

 vibratory. In this matter the priority in a wider view 

 rests with Clausius. According to Waterston the ratio of 

 specific heats should be (as for mercury vapour) r67 in 

 all cases. Again, although he was well aware that the 

 molecular velocity cannot be constant, there is no antici- 

 pation of the law of distribution of velocities established 

 by Maxwell. 



'•A large part of the paper deals with chemistry, and 

 shows that his views upon that subject also were much in 

 advance of those gener.tlly held at the time. 



" The following extract from a letter by Prof. McLeod 

 will put the reader into possession of the main facts of 

 the case : — 



"' It seems a misfortune that the paper was not printed 

 when it was written, for it shadows forth many of the 

 ideas of modern chemistry which have been adopted 

 since 1845, and it might have been the means of hastening 

 their reception by chemists. i 



" ' The author compares the masses of equal volumes of , 

 gaseous and volatile elements and compounds, and taking 

 the mass of a unit volume of hydrogen as unity, he j 

 regards the masses of the same volume of other volatile | 

 bodies as representing their molecular weight, and in the 

 case of the elements he employs their symbols to indicate ! 

 the molecules. 



" ' In water he considers that the molecule of hydrogen ' 

 is combined with half a molecule of oxygen, forming one of 

 steam, and he therefore represents the compound as HOj. j 

 He does not make use of the term " atom " (although he 

 speaks of atomic weight on p. 18, but thinks it divisible), 

 and if he had called the smallest proportion of an element i 

 which enters into combination an atom, he would prob- ; 

 ably have been led to believe that the molecules of some \ 

 of the simple bodies contain two atoms, and he might 

 have adopted two volumes to represent the molecule, as 

 is done at the present time. The author calls one volume j 

 or molecule of chlorine CI, one volume or molecule of \ 

 hydrogen H, and one volume or molecule of hydrochloric j 

 acid HjClj. If he had regarded the molecules as con- ' 

 taining two indivisible atoms, these bodies would have : 

 been represented, as now, by the formulas Cl^, H.,, and I 

 HCl respectively, all occupying two volumes. § 15 "shows j 

 how near he was to this conception. Gerhardt, in the ' 

 fourth part of his " Trait^ de Chimie Organique," pub- 

 lished in 1856, points out the uniformity introduced into 

 chemical theory by the adoption of this system. 



"'For carbon he makes C = 12, as now accepted, i 

 although I do not find how he arrives at this number. He 

 seems to have anticipated one of Ramsay's recent dis- 

 coveries, that nitrous anhydride (hyponitrous acid, ONs, 

 No. 26 in the table) dissociates on evaporation into nitric j 

 oxide (binoxide of nitrogen, No. 23) and nitric peroxide ^ 

 (nitrous acid. No. 25). 



" ' The values for the symbols for sulphur, phosphorus, 

 and arsenic, taken from the vapour densities (and which 

 are multiples of what are believed to be the true atomic 

 weights), cause some complexity in the formulas of their 

 compounds. 



"'There seem to be errors in the formulae of alcohol | 

 and ether on p. 49, for they do not agree with those in the 1 

 table. They ought probably to be written j 



2(HQ) + Oi2Hi and 4(HCj) + OpHi. I 



" ' Considering how nearly Waterston approached what 

 is now believed to be the true theory, it is disappointing 

 to read his controversy with Odling in 1863 and 1864 

 {Phil. Mag., vols. xxvi. and xxvii.), where he seems to 

 oppose the new formulae then being introduced. He is 

 very dogmatic about the constitution of hydrate of potash : 



NO. I I 76, VOL. 46] 



he very properly insists that we can only obtain a know- 

 ledge of the molecular weight of bodies that can be 

 volatilized, and of which the vapour densities can be de- 

 termined, but he does not see the analogy between the 

 hydrate and oxide of potassium with alcohol and ether, 

 probably because he regards these latter bodies as com- 

 Ijinations of water with different quantities of olefiant gas. 

 He writes water HOj = 9, alcohol CHsHOj = 23, and 

 ether C.2H4 . HOj = 37, whilst he considers potassic 

 hydrate KO^ . HOi = 56, and oxide of potassium 

 KOi = 47, the hydrate having a higher molecular weight 

 than the oxide. If we regard these compounds as derived 

 from water by the replacement of hydrogen by ethyl and 

 potassium respectively, the analogy between the two 

 series is complete (ethyl was discovered in 1849, and is 

 mentioned by Waterston). 



H2O = 18 



(C2H5)HO = 46 



(CoH5).20 = 74 



HoO - 18. 

 KHO = 56. 

 K2O - 94. 



"' From a remark in the Phil. Mag. (vol. xxvi. p. 520)^ 

 I imagined that Waterston had arrived at the double 

 atomic weights of many of the metals now adopted, for he 

 gives that of iron as 56 and that of aluminium as 27, 

 calculated from their specific heats, but there is an error 

 in his arithmetic, for 33 divided by the specific heat of 

 iron -1138 gives 28-998, and 3-3 divided by the specific 

 heat of aluminium "2143 gives 15 399.' 



*• With the exception of some corrections relating merely 

 to stops and spelling, the paper is here reproduced exactly 

 as it stands in the author's manuscript. — December 1891."' 



The author's own introduction to his memoir, which 

 occupies eighty pages of the Philosophical Transactions 

 as now printed, runs as follows : — 



" Of the physical theories of heat that have claimed 

 attention since the time of Bacon, that which ascribes 

 its cause to the intense vibrations of the elementary 

 parts of bodies has received a considerable accession 

 of probability from the recent experiments of Forbes 

 and Melioni, It is admitted that these have been the 

 means of demonstrating that the mode of its radiation 

 is identical with that of light in the quantities of re- 

 fraction and polarization. The evidence that has 

 been accumulated in favour of the undulatory theory 

 of light has thus been made to support with a great 

 portion of its weight a like theory of the phenomena of 

 heat ; and we are, perhaps, justified in expecting that the 

 complete development of this theory will have a much 

 more important influence on the progress of science,^ 

 because of its more obvious connection and intimate 

 blending with almost every appearance of Nature. Heat 

 is not only the subject of direct sensation and the vivifier 

 of organic life, but it is manifested as the accompaniment 

 of mechanical force. It is related to it both as cause and 

 effect, and submits itself readily to measurement by means 

 of the mechanical changes that are among the most pro- 

 minent indications of its change of intensity. The un- 

 dulatory theory at once leads us to the conclusion that, 

 inasmuch as the temperature of a body is a persistent 

 quality due to the motion of its molecules, its internal 

 constitution must admit of it retaining a vast amount of 

 living force. Indeed, it seems to be almost impossible 

 now to escape from the inference that heat is essentially 

 molecular vis viva. In solids, the molecular oscillations 

 may be viewed as being restrained by the intense forces 

 of aggregation. In vapours and gases these seem to be 

 overcome ; vibrations can no longer be produced by the 

 inherent vis itisita of the molecules struggling with attrac- 

 tive and repellent forces ; the struggle is over and the 

 molecules are free ; but they, nevertheless, continue to 

 maintain a certain temperature ; they are capable of 

 heating and being heated ; they are endowed with the 



