VI.] THE MOTIVE POWERS OF THE UNIVERSE. 59 



atmosphere ; and the energy of motion that they had as 

 planets is transformed into heat by friction against the air.^ 

 Their brilliant light is due to intense heat, and when they 

 fall as meteoric stones, these stones are intensely hot. 

 This is at least a possible origin of solar heat. It is 

 calculated that a meteor, falling into the sun's atmosphere 

 with the velocity of a planet at the surface of his atmo- 

 sphere (and it cannot fall in with a less velocity than this), 

 has energy of motion enough to be converted into a rather 

 greater quantity of heat than would be produced by the 

 combustion of four thousand times its weight of coal.^ 



This hypothesis has received a very strong confirmation Carring- 

 by Mr. Carrington and another observer simultaneously, at yation^^*^^' 

 different places, on the 1st September, 1859, seeing two 

 meteor-Like bodies of such brightness as appeared bright 

 against the sun, suddenly appear, rapidly move across his 

 disc from vjest to east, and soon disappear. 



There are some further reasons in favour of the meteoric 

 theory which are little known, and are worth stating here.^ 



If there are small planets revolving round the sun and 

 constantly falling into his atmosphere as meteors, they 

 probably occupy, like the entire solar system, a lenticular 

 (or very oblate spheroidal) space, having its greatest 

 diameter nearly coincident with the sun's equator; and 

 if so, a greater number of meteors must fall on the equa- 

 torial than on the polar regions of the sun, making the 

 former the hottest. Such is the case. Secchi of Eome, Sun 

 without any theory to support, has found by the use of a liottest 

 thermo-electric test (the result of which is due not to the equator, 

 ratio but to the difference of the two sources of heat) that ^"*^ ^^^' 

 the sun's equator is sensibly hotter than his poles.* 



^ And also, as lias been suggested, by the compression of the air before 

 them as they faU. It is to be remembered, however, that equal quantities 

 of energy of motion are convertible into equal quantities of heat, in what- 

 ever way the transfoiTnation is effected. 



^ TyndaU. on Heat as a Mode of Motion. 



^ What follows, on the motions of the solar spots, and on the difference 

 of temjieratiire at the sun's poles and equator, was first published by me in 

 a paper read at the Newcastle meeting of the British Association in 1863, 

 and printed in its Transactions. 



* Nichol's Cyclopaedia of Mathematical and Physical Science. 



