230 THE POPULAR SCIENCE MONTHLY. 



eluding " carbon, hydrogen, nitrogen, and probably oxygen," while, 

 according to the views set forth by Dewar and Liveing, it also con- 

 tains nitrogenous compounds such as cyanogen. 



Adversely to the assumption that interplanetary space is filled with 

 gases, it is urged that the presence of ordinary matter would cause 

 sensible retardation of planetary motion, such as must have made itself 

 felt before this ; but, assuming that the matter filling space is an al- 

 most perfect fluid not limited by border surfaces, it can be shown on 

 purely mechanical grounds that the retardation by friction through 

 such an attenuated medium would be very slight indeed, even at plan- 

 etary velocities. 



But it may be contended that, if the views here advocated regard- 

 ing the distribution of gases were true, the sun should draw to him- 

 self the bulk of the least diffusible, and therefore the heaviest gases, 

 such as carbonic acid, carbonic oxide, oxygen, and nitrogen, whereas 

 spectrum analysis has proved, on the contrary, a great prevalence of 

 hydrogen. 



In explanation of this seeming anomaly, it can be shown, in the 

 first place, that the temperature of the sun is so high that such com- 

 pound gases as carbonic acid and carbonic oxide could not exist within 

 him, their point of dissociation being very much below the solar tem- 

 perature. It has been contended, indeed, by Mr. Lockyer, that none 

 of the metalloids have any existence at these temperatures, although 

 as regards oxygen Dr. Draper asserts its existence in the solar photo- 

 sphere. There must be regions, however, outside that thermal limit, 

 where their existence would not be jeopardized by heat ; and here 

 great accumulation of the comparatively heavy gases that constitute 

 our atmosphere would probably take place, were it not for a certain 

 counterbalancing action. 



I here approach a point of primary importance in my argument, 

 upon the proof of which my further conclusions must depend. 



The sun completes one revolution on its axis in twenty-five days, 

 and its diameter being taken at 882,000 miles, it follows that the 

 tangential velocity amounts to 1*25 miles per second, or to what the 

 tangential velocity of our earth would be if it occupied five hours 

 instead of twenty-four in accomplishing one revolution. This high 

 rotative velocity of the sun must cause an equatorial rise of the solar 

 atmosphere, to which Mairan, in 1731, attributed the appearance of 

 zodiacal light. Laplace rejected this explanation on the ground that 

 zodiacal light extended to a distance from the sun exceeding our own, 

 whereas the equatorial rise of the solar atmosphere due to its rotation 

 could not exceed nine twentieths of the distance of Mercury. But it 

 must be remembered that Laplace based his calculation upon the 

 generally accepted hypothesis of an empty stellar space (occupied 

 only by an imaginary ether), and it can be shown that the result of 

 solar rotation would be widely different, if supposed to take place 



