432 THE SCIENTIFIC PAPERS OF 



that the condition of the gaseous fuel supplying the sun may vary 

 according to the state of previous decomposition, in which other 

 heavenly bodies may have taken part. May it not be owing to 

 such differences in the quality of the fuel supplied that the ob- 

 served variations of the solar heat may depend ? and may it not 

 be in consequence of such changes in the thermal condition of the 

 photosphere that sun-spots are formed ? 



The views here advocated could not be thought acceptable 

 unless they furnished at any rate a consistent explanation of the 

 still somewhat mysterious phenomena of the zodiacal light and of 

 comets. Regarding the former, we should be able to return to 

 Mairan's views, the objection by La Place being met by a continu- 

 ous outward flow from the solar equator. Luminosity would be 

 attributable to particles of dust emiiting light reflected from the 

 sun, or by phosphorescence. But there is another cause for lumi- 

 nosity of these particles, which may deserve a passing consideration. 

 Each particle would be electrified by gaseous friction in its accelera- 

 tion, and its electric tension would be vastly increased in its forcible 

 removal, in the same way as the fine dust of the desert has been 

 observed by Werner Siemens to be in a state of high electrification 

 on the apex of the Cheops Pyramid. Would not the zodiacal light 

 also find explanation by slow electric discharge backward from the 

 dust towards the sun ? and would the same cause not account for 

 a great difference of potential between the sun and earth, which 

 latter may be supposed to be washed by the solar radial current ? 

 May not the presence of the current also furnish us with an ex- 

 planation of the fact that hydrogen, while abounding apparently 

 in space, is practically absent in our atmosphere, where aqueous 

 vapour, which may be partly derived from the sun, takes its place ? 

 An action analogous to this, though on a much smaller scale, may 

 be set up also by terrestrial rotation giving rise to an electrical 

 discharge from the outgoing equatorial stream to the polar regions, 

 where the atmosphere to be pierced by the return flood is of least 

 resistance. 



It is also important to show how the phenomena of comets 

 could be harmonised with the views here advocated, and I venture 

 to hope that these occasional visitors will serve to furnish us with 

 positive evidence in my favour. Astronomical physicists tell us 

 that the nucleus of a comet consists of an aggregation of stones 



