302 THE ADDRESSES, LECTURES, ETC., OF 



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 almost 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 planetary velocities. 



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

 regarding the distribution of gases were true, the sun should draw 

 to himself 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 

 compound gases as carbonic acid and carbonic oxide could not 

 exist within him, their point of dissociation being very much 

 below the solar temperature. 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 photosphere. There must be regions, 

 however, outside that thermal limit, where their existence would 

 not be jeopardised 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. La Place rejected this explana- 

 tion 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 



