108 



SCIENCE. 



|VoL. II., No. 25. 



to the course of practical events appearing in 

 public affairs cannot aff'orcl to ignore their 

 strongest opponent. 



The evolution which is discovered every- 

 where in nature, to be properly demonstrated, 

 must have its explanation set forth in three 

 parts. First, it must be explained why there 

 is change, for without change there can be 

 no development; second, it must be shown 

 b3' what agency change results in progress, 

 for change to inferior or co-ordinate conditions 

 is not evolution ; and, third, what is the course 

 of progress, for, if there is progress, it must be 

 in some direction that can be determined, an* 

 thus science becomes prophetic. 



Of the three departments of sociology, — 

 namety, the causes of social change, the causes 

 of social progress, and the course of social 

 progress-, — the work under consideration, as 

 its name indicates, is devoted to but one, 

 — the cause of social progress ; though it in- 

 cidentally discusses many of the subjects of 

 evolution in other branches of science, and 

 the author ultimately reaches the conclusion 

 that education is the chief means to secure 

 social progress, and thus secure human hap- 

 piness. 



SIEMENS' SOf.AR ENERGY. 



On the conservation of solar energy : a collection of 

 papers and discussions. By C. Williams Sie- 

 mens, F.R.S., D.C.L. London, Macniillan §■ 

 Co., 1883. 20+111 p. 8°. 

 This is a collection of the original paper 

 read before the Eoyal society b}- Siemens, and 

 the criticisms from Fitzgerald, Faj-e, Hirn, 

 Archibald, and others, together with the re- 

 plies of Siemens. 



The theory, well summed up on p. 22, sup- 

 poses that space is filled with aqueous vapor 

 and carbon compounds ; that these, at low 

 pressures, are dissociated b}' the radiant ener- 

 gjr of the sun ; that the dissociated elements 

 are drawn into the sun at its poles, unite, and 

 generate heat sufficient to give a temperature 

 of about 2,800° C. ; and that the aqueous va- 

 por and carbon compounds formed are again 

 thrown off' by centrifugal force at the sun's 

 equator. 



As evidence of the presence of carbon va- 

 pors in space, Siemens refers to the analyses 

 of meteors, which in some cases have proved 

 that hydrocarbons were a component of the 

 meteoric mass, and again to the work of Abnej' 

 and Langlej' on the absorption of the radiant 

 energy of the sun. 



The dissociation of vapors at low tensions 



is a point which seems to be well estabiislied. 

 One of the earliest proofs is given in Prof. J. 

 Willard Gibbs's paper on the equilibrium of 

 heterogeneous substances.' He shows, that 

 in a mixture of gases, as of oxygen, hydro- 

 gen, and vapor of water, in which the vapor 

 is formed with a decrease in volume from tliat 

 of the components, it is possible to assign a 

 value to the tension such that the mixture may 

 be in a state of dissipated energy ; i.e.. in such 

 a condition that the energy of the system is a 

 minimum for its entrop3- ; and that any change 

 in energy can be brought about onlj- bj' work 

 done bj' some outside system and in propor- 

 tion to that outside work. In such a state, 

 nothing of the nature of an explosion could be 

 caused bj' an electric spark : the elements 

 would cease to show the phenomenon of chem- 

 ical affinitj-. Willard Gibbs writes, "It maj', 

 indeed, be true, that at ordinaiy temperatures, 

 except when the quantity either of hydrogen 

 or of oxj-gen is very small compared witb the 

 quantity of water, the state of dissipated en- 

 ergy is one of such extreme rarefaction as to 

 lie entirely bej'ond our power of experimental 

 verification." In the formula from which 

 these results are deduced, the ratio occurs of 

 the amounts of the components to that of the 

 compound, these' amounts being raised to 

 small powers. This explains the qualification 

 as to the amount of components which may 

 exist in a free state. 



This last condition may have an important 

 bearing on the possibilitj' of the truth of Sie- 

 mens' theory ; for, although Gibbs has shown 

 that dissociation may occur in rarefied vapors, 

 still the amount of the dissociation is limited 

 unless the rarefaction be very great. 



Some two or three years ago Professor Og- 

 den Rood succeeded in getting experimental 

 evidence of dissociation iu rarefied gases at 

 ordinaiT temperatures, but has never published 

 his results. 



Dr. Siemens gives, on p. 13, what evidence 

 he earlj' obtained of dissociation of gases in 

 vacuum tubes under the influence of sunlight. 

 What he has done since may be found from an 

 account of his recent lecture at the Ro^'al in- 

 stitution {Nature, Maj- 3). Objections to the 

 theory are well put by Fitzgerald when he asks 

 (p. 41) "how the interplanetary gases near the 

 sun acquire a sufficient radial velocity to pre- 

 vent their becoming a dense atmosphere round 

 him ; whj' enormous atmospheres have not long 

 ago become attached to the planets, notably to 

 the moon ; whj' the earth has not long ago been 

 deluged when a constant stream of aqueous 



1 Proc. Conn. acnd. BC, iii. 



