SIR WILLIAM SIEMENS, F.R.S. 427 



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 he 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 anhydride, carbonic oxide, oxygen and 

 nitrogen, whereas spectrum analysis has proved on the contrary a 

 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 anhydride and carbonic oxide, could not 

 exist within him ; it has been contended, indeed, by Mr. Lockyer, 

 that none of the metalloids have any existence at these tempera- 

 tures, although as regards oxygen, Dr. Draper asserts its existence 

 in the solar photosphere. There must be regions, however, out- 

 side that thermal limit, where their existence would not be 

 jeopardised by heat, and here great accumulation of those com- 

 paratively heavy gases that constitute our atmosphere would 

 probably take place, were it not for a certain counterbalancing 

 action. 



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

 upon the proof of which my further conclusions must depend. 



The sun completes one revolution on its axis in 25 days, and its 

 diameter being taken at 882,000 miles, it follows that the tan- 

 gential velocity amounts to 1*25 miles per second, or to 4*41 times 

 the tangential velocity of our earth. 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 the 

 zodiacal light. La Place rejected this explanation on the ground 

 that the zodiacal light extended to a distance from the sun ex- 

 ceeding our own distance, whereas the equatorial rise of the solar 

 atmosphere due to its rotation could not exceed ^ths of the 

 distance of Mercury. But it must be remembered that La Place 

 based his calculation upon the hypothesis of an empty stellar 

 space (filled only with an imaginary ether), and that the result of 



