308 THE ADDRESSES, LECTURES, ETC., OF 



existence of an intermediate neutral atmosphere, called the 

 penumbra. 



As the whole solar system moves through space at a pace esti- 

 mated at 150,000,000 of miles annually (being about one-fourth 

 of the velocity of the earth in its orbit), it appears possible that 

 the condition of the gaseous fuel supplying the sun may vary 

 according to its state of previous decomposition, in which other 

 heavenly bodies may have taken part, and whereby an interesting 

 reflex action between our sun and other heavenly bodies would 

 be brought about. May it not be owing to such differences in 

 the quality of the fuel supplied that the observed variations of 

 the solar heat may arise ? and may it not be in consequence 

 of such changes in the thermal condition of the photosphere 

 that the extraordinary convulsions revealed to us as sun-spots 

 occur ? 



The views here advocated could not be thought acceptable 

 unless they furnished at any rate a consistent explanation of the 

 Btill somewhat mysterious phenomena of the zodiacal light and of 

 comets. Eegarding the former, we should be able to revert to 

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

 tinuous outward flow from the solar equator. Luminosity would 

 be attributable to particles of dust emitting light reflected from 

 the sun, or to phosphorescence. But there is another cause for 

 luminosity of these particles, which may deserve serious considera- 

 tion. Each particle would be electrified by gaseous friction in its 

 acceleration, 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 Dr. Werner Siemens to be in a state of high 

 electrification on the apex of the Cheops pyramid. Could not the 

 zodiacal light also be attributed to slow electric discharge back- 

 ward from the dust towards the sun ? and would not the same 

 cause 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 radial solar current 

 also furnish us with an explanation of the fact that hydrogen, 

 while abounding apparently in space, is practically absent in our 

 atmosphere, where aqueous vapour and carbonic acid, which would 

 come to us directly from the sun, take its place ? An action 

 analogous to this, though on a much smaller scale, may be set up 



