ASTRONOMY. 393 



These drawings agree, and both of them correspond unmistakably u ith 

 the eclipse photograph. I think I may venture to say that there can no 

 longer remain any doubt as to the true solar origin of the main details 

 of the photographs taken of the eclipse up to 8' to 10' from the limb. 

 Arrangements are in progress for experiments at a good elevation." 



On the conservation of solar energy : a collection of papers and discus- 

 sions. By C. William Siemens. London, 1883. — This is a collection 

 of the original paper read before the Eoyal Society by Siemens, and 

 the criticisms from Fitzgerald, Faye, Hirn, Archibald, and others, to- 

 gether with the replies of Siemens. 



The theory, well summed up on p. 22, supposes that space is filled 

 with aqueous vapor and carbon compounds ; that these, at low press- 

 ures, are dissociated by the radiant energy of the sun ; that the disso- 

 ciated 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 vapor and carbon compounds formed are again thrown off by 

 centrifugal force at the sun's equator. 



As evidence of the presence of carbon vapors in space, Siemens refers 

 to the analyses of meteors, which in some cases have proved that hy- 

 drocarbons were a component of the meteoric mass, and again to the 

 work of Abney and Langley 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 established. One of the earliest proofs is given in Prof. J. Wil- 

 lard Gibbs's paper on the equilibrium of heterogeneous substances. 



Some two or three years ago Prof. Ogden Eood succeeded in getting 

 experimental evidence of dissociation in rarefied gases at ordinary tem- 

 peratures, but has never published his results. 



Dr. Siemens gives, on p. 13, what evidence he early obtained of dis- 

 sociation 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 Eoyal Institution {Nature, May 3). Objections to the 

 theory are well put by Fitzgerald when he asks (p. 41) " how the inter- 

 planetary gases near the sun acquire a sufficient radial velocity to pre- 

 vent their becoming a dense atmosphere round him ; why enormous at- 

 mospheres have not long ago become attached to the planets, notably 

 to the moon ; why the earth has not long ago been deluged when a con- 

 stant stream of aqueous vapor, that would produce a rain of more than 

 30 inches per annum all over the earth, must annually pass out past 

 the earth in order to supply fuel to be dissociated by the heat that an- 

 nually passes the earth ; and why we can see the stars, although most 

 of the solar radiations are absorbed within some reasonable distance of 

 the sun." 



Faye objects that the presence of such a resisting medium in space 

 as the vapor is not to be accepted, with our present knowledge, and 

 that the '•ontrifugal force at the sun's equator is far too small for the 

 action required. 



