106 ANNUAL OF SCIENTIFIC DISCOVERY. 



these bodies are too few in number is met by the fact, that at one 

 observatory alone as many as 240,000 have been observed in nine 

 hours. 



Meteoric bodies attracted by the sun would necessarily move with 

 a high and rapidly accelerating velocity, and it is calculated that a 

 body falling into the sun at a velocity of three hundred and ninety 

 miles a second would attain a temperature nine thousand times that 

 produced by the combustion of coal. A body the size of the earth 

 falling into the sun would supply its heat for about one hundred years, 

 but would make no appreciable increase in its bulk ; and were the 

 earth's motion suddenly arrested, the heat developed would raise the 

 temperature to such a degree that the elements would be dissipated in 

 vapor. Notwithstanding the difficulties in the way of receiving this 

 theory of Dr. Mayer's, it was regarded by Dr. Tyndall as that which 

 offered the best explanation of the cause of solar heat. 



PERMANENCE OF THE SOLAR SYSTEM. 



One of the most interesting questions which have arisen from the 

 investigations of modern science into the general laws of nature is that 

 of the stability of our universe as at present constituted. Is this sys- 

 tem fitted to run on forever, in accordance with its present laws, or 

 will these laws, in the end, lead to its subversion ? The conclusion 

 was reached by Laplace, and has been confirmed by subsequent in- 

 vestigators, that, so far as the force of gravitation alone is concerned, 

 the system is stable. Every change which the attraction of one planet 

 produces in the orbit of another will finally induce its own compensa- 

 tion, and bring the system back to its original state. But the discov- 

 eries of the present century respecting the correlation of the different 

 forces of nature, the conservation of force in general, the nature of 

 the solar light and heat, and the motions of the comets, seem to indi- 

 cate that gravitation is by no means the only force by which the 

 motions of the heavenly bodies are influenced, and that causes which 

 slowly but surely undermine the system are in operation : that the 

 latter is not, therefore, a self-winding clock which may run forever, 

 but that it must ultimately lose all motion, unless some power, capa- 

 ble of controlling the laws of material nature, shall interfere to pre- 

 serve it. We shall give some examples of these destructive forces. 



In the first place, the sun is radiating heat into space in quantities 

 incomparably greater than it receives. If it were not so, we should 

 receive on the average as much heat from every other quarter of the 

 heavens as from the sun, and no vicissitudes of temperature could 

 ever occur on earth. From what we know of the nature of heat, 

 it is impossible that the supply contained in the sun should be abso- 

 lutely infinite. The sun must, therefore, as centuries advance, grow 

 cooler and cooler, until its heat is entirely lost. This will be followed 

 by the cooling of the. earth, and thus all life on our planet must cease, 

 or the conditions of its existence must be completely changed. It 

 may be asked, Is it certain that the heat of the sun is not returned to 

 it in some other form ? It is, of course, impossible to give any abso- 

 lute and direct proof that the sun does not receive heat, or its equiv- 

 alent, from some unknown source ; but it is certain that we can trace 

 the operation of no natural law which would tend to return heat to 



