243 



enouah very nearly to balance solar gravitation upon it everywhere, 

 except close to the sun's surface. The meteors themselves probably 

 evaporate somewhere near the sun, merely on account of the high 

 temperature of that part of space, but ultimately losing their rotatory 

 motion by intense resistance in entering the sun's atmosphere, be- 

 come condensed into a liquid state by solar gravitation, and come to 

 rest in the sun. The quantity of heat thus generated in the region 

 of intense resistance, by any quantity of matter falling in, wUl 

 exceed half the equivalent of the work done by solar gravitation on 

 an equal mass moving from an infinite distance by (what must 

 probably be quite insensible in comparison) the latent heat evolved 

 in condensation, together with the heat of any chemical combination 

 that may take place. The other half of the work done by solar gra- 

 vitation on every meteor which has come from an infinite distance 

 (or from many times the sun's radius off), goes to generate heat in 

 inter-planetary air by friction. 



The meteoric matter thus added to the sun, to generate heat at 



the present rate of emission as determined by Pouillet, if settling 



at the surface with the same as his mean density, would cover it 



about sixty feet thick in a year, and would not increase his apparent 



dimensions by more than about 1" in 40,000 years ; or in 2,000,000 



years, by as much as he appears to grow from July to December. 



It must, therefore (whatever be the actual density of the deposit), 



be insensible from the earliest historical period of observation till 



the present time; and for thousands of years to come, if continued 



only at the same rate, it must remain neither demonstrated nor 



disproved by the most accurate measurements of the sun's apparent 



magnitude. 



The approximate equality of solar heat in all regions of his sur- 

 face is probably due to the distillation of the meteors, which if solid 

 when entering the region of intense resistance, would probably give 

 an immensely more copious supply in the equatorial than in the 

 polar regions. The dark spots are probably whirlwinds, analogous 

 to the hurricanes in the tropical regions of the earth's atmosphere, 

 (although produced by a different cause,*) which by centrifugal 



* The friction of the vortices of meteoric vapour close round the sun, upon 

 the atmosphere between them, and his surface revolving at the comparatively 

 slow rate of once in twenty-five days, probably gives rise to eddies sometimes 



