R. Meldola—Bright Lines in the Solar Spectrum. 299 
magnetic characters of this gas consequent on variation of tem- 
rature, 
Sir William Thomson’s theory of the dissipation of energy 
leads to the belief that the sun, like other stars, is gradually 
cooling down. Thus we should be led to infer @ priori that 
there must be a period in the life of a star when compounds 
can begin to form. Such combination would begin in the 
Outer and cooler portions of the star's atmosphere, as required 
"y the present hypothesis, and would be attended with the 
development of the heat representing the energy of chemical 
Separation. As the star goes on cooling down, the zone of 
Combustion, at first a mere shell, would gradually encroach 
upon the central regions, and a star haying permanently bright 
* See Bunsen’s experiments on the combustion of different mixtures of CO and 
H with 0 (Pogg. Ann., exxxi, 161); also Berthelot On the Chemical Equilibrium 
of C, H and O (Bull. Soc. Chim, [2] xii, 99). 
+I may here recall the much discussed observation of Secchi, who asserted 
the ¢ of water vapor in neigh! ‘ 
ae 238). Janssen also, in 1864, observed aqueous vapor in 
1 yee Ing in 1868, in the atmosphere of many other stars (Compt. Rend., 
