1868.] 



Constitution of the Sun and Stai's. 



15 



constituent, viz. the vapour of water, it will form an exception to the rule, 

 inasmuch as it will be unable to maintain its footing more than a little 

 beyond the limits of the lightest of the abundant constituents, which in 

 the case of the earth's atmosphere is nitrogen. 



26. It becomes of importance, then, to arrange the constituents of the 

 solar atmosphere in the order of the masses of the molecules, as this will 

 be the order in which the surfaces of their successive atmospheres will 

 succeed one another. A provisional attempt is made in the following table 

 to arrange on this principle the better-known of the elementary substances, 

 including all the bodies whose spectra have yet been compared with the 

 spectrum of the sun, or with those of other celestial bodies. The posi- 

 tion in the list of those substances whose names are printed in ordinary- 

 type has been ascertained by direct observations on the vapour-densities, 

 and may be depended on ; but all the rest, which are printed in italics, are 

 placed on the provisional supposition that the masses of their molecules 

 when in the state of vapour are proportional to their generally received 

 atomic weights. It is probable that in some of these instances the mass is 

 proportional to some simple multiple or submultiple of the atomic weight, 

 and that the position in the list ought to be altered accordingly. We 

 shall find grounds for concluding that this is the case with Barium, and 

 that it ought to be placed in the list probably between zinc and selenium, 

 perhaps between calcium and titanium, or between sulphur and chlorine. 



Table I. Table of Elementary Substances arranged in the order of their 

 Vapour-densities where these are known, and in the order of the 

 Atomic weights where the Vapour-densities are not known. 



Elements. 



Observed 

 vapour- 

 density, 

 that of air 

 being the 

 unit. 



Observed 

 vapour- 

 density, 

 that of 

 hydrogen 

 being the 

 unit. 



Presumed masses of 

 the gaseous mole- 

 cules, that of hy- 

 drogen being the 

 unit. 



Whether 

 present in the 

 sun's atmo- 

 sphere or not. 



Hvdrogen 



Lithium 



•0692 



1 



1 which is H 

 7 „ L 

 9-3 „ a 

 . 10-9 „ B 

 12 „ C 

 14 „ N 

 16 „ O 

 19 „ F 

 23 „ Na 

 24-3 „ Mg 

 27-5 „ Al 

 28 „ Si 

 32 „ S 

 35-5 „ CI 

 39-1 „ K 

 40 „ Ca 

 50 „ Ti 



present, 

 not. 



not. 

 not. 



present, 

 present, 

 doubtful, 

 doubtful. 



doubtful, 

 present. 



Boron 













Oxygen 



•9713 

 11056 



14- 04 



15- 98 









Magnesium 







Sulphur above 1000° C 

 Chlorine 



Calcium 



2-23 

 2-47 



32-23 

 35-69 



Titanium 







