1882.J On the Conservation of Solar Energy, 397 



radial current ? May not the presence of the current also furnish us 

 •with an explanation of the fact that hydrogen, while abounding appa- 

 rently 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 similar to meteoric stones. 

 Adopting this view, and assuming that the stones have absorbed in 

 stellar space gases to the amount of six times their volume, taken at 

 atmospheric pressure, what it may be asked, will be the effect of such 

 a mass of stone advancing towards the sun at a velocity reaching in 

 perihelion the prodigious rate of 366 miles per second (as observed 

 in the comet of 1845), being twenty- three times our orbital rate of 

 motion. It appears evident that the entry of such a divided mass into 

 a comparatively dense atmosphere must be accompanied by a rise of 

 temperature by frictional resistance, aided by attractive condensation. 

 At a certain point the increase of temperature must cause ignition, 

 and the heat thus produced must drive out the occluded gases, which 

 in an atmosphere 3000 times less dense than that of our earth would 

 produce 6x3000 = 18,000 times the volume of the stones themselves. 

 These gases would issue forth in all directions, but would remain 

 unobserved except in that of motion, in which they would meet the 

 interplanetary atmosphere with the compound velocity, and form a zone 

 of intense combustion, such as Dr. Huggins has lately observed to 

 surround the one side of the nucleus, evidently the side of forward 

 motion. The nucleus would thus emit original light, whereas the tail 

 may be supposed to consist of stellar dust rendered luminous by reflex 

 action produced by the light of the sun and comet combined, as fore- 

 shadowed already by Tjmdall, Tate, and others, starting each from 

 different assumptions. 



These are in brief the outlines of my reflections regarding this most 

 fascinating question, which I venture to put before the Royal Society. 

 Although I cannot pretend to an intimate acquaintance with the more 

 intricate phenomena of solar physics, I have long had a conviction, 

 derived principally from familiarity with some of the terrestrial 

 effects of heat, that the prodigious and seemingly wanton dissipation 

 of solar heat is unnecessary to satisfy accepted principles regarding 

 the conservation of energy, but that it may be arrested and returned 

 over and over again to the sun, in a manner somewhat analogous 



2 g 2 



