ATOMS AND STTNP.EAMS.* 



Bv Sir Robert 1 5 all, V. 11. S. 



In recent years an important change has taken phice in the manner 

 in which many physical problems are approached. The philosopher 

 who now seeks an explanation of great natural x)henomena not unfre- 

 qnently finds much assistance from certain remarkable discoveries as to 

 the ultimate constitution of matter. Many an obscure question in 

 physics has been rendered clear when some of the properties of mole- 

 cules have been brought to light. No d(mbt our knowledge of the 

 natural history of the molecule is still vastly wanting in detail. It 

 must however be admitted that we have traced an outline of that 

 wonderful chapter in nature which is specially serviceable in the (jues- 

 tion which I now i^ropose to discuss. 



The iiroblem before us may be stated in the following terms. We 

 have to illustrate how the sun is enabled to maintain its tremendous 

 expenditure of light and heat without giving any signs of npiiproaching 

 exhaustion. It will be found that the atomic theory of the constitu- 

 tion of matter exhibits the mechanism of the process by which that 

 capacity of the great luminary for supplying the radiation so vital to 

 the welfare of mankind is sustained from age to age. 



Let me here anticipate an objection which may not improbably be 

 raised. Those who have paid attention to this subject are aware that 

 the remarkable doctrine first propounded by Helndioltz removed all 

 real doubt from the matter. It is to this eminent philosopher we owe 

 an explanation of what at hrst seemed to be a paradox. He explained 

 how, notwithstanding that the sun radiates its heat so profusely, no 

 indications of the inevitable decline of heat can be as yet discovered. 

 If the sun luul been nnide of solid coal from center to surface, and if 

 that coal had been burned for the purpose of sustaining the radiation, 

 it can be demonstrated that a few thousand years of solar exxienditure 

 at the present rate would suffice to exhaust all the heat which the com- 

 bustion of that great si)here of fuel could generate. We know how 

 ever that the sun has been radiating heat, not alone for thousands of 

 years, but for millions of years. The existence of fossil plants and ani- 

 mals would alone suffice to demonstrate this fact. We have thus to 



* From The Fortnightly Review October, 1893 ; vol. Liv, pp. 464-477. 



121 



