158 Intelligence and Miscellaneous Articles. 



the globe, become ohjects of the greatest importance in connexion 

 with the atmosphere which surrounds it. Three-fourths of the whole 

 mass of the air is within range of the influence of the highest moun- 

 tains; one-half of the air and nearly nine-tenths of the vapour are 

 concentrated within ahout 19,000 feet of the sea-level, a height 

 which hardly exceeds the mean level of the crest of the Himalaya ; 

 while one-fourth of the air and one-half of the vapour are found be- 

 low a height of 8500 feet. Thus, mountains even of moderate mag- 

 nitude may produce important changes in very large masses of the 

 atmosphere, as regards their movements, their temperature, and their 

 hygrometric state ; and especially in those strata that contain the 

 great bulk of the watery vapour, and that have the greatest effect 

 therefore in determining the character of climate. 



XXII. Intelligence and Miscellaneous Articles. 



PHYSICAL CONSIDERATIONS REGARDING THE POSSIBLE AGE OF 

 THE SUN'S HEAT. BY PROFESSOR W. THOMSON*. 



^HE author prefaced his remarks by drawing attention to some 

 principles previously established. It is a principle of irreversible 

 action in nature, that, '" although mechanical energy is indestructible, 

 there is a universal tendency to its dissipation, which produces 

 gradual augmentation and diffusion of heat, cessation of motion, 

 and exhaustion of potential energy, through the material universe." 

 The result of this would be a state of universal rest and death, if 

 the universe were finite and left to obey existing laws. But as no 

 limit is known to the extent of matter, science points rather to an 

 endless progress through an endless space, of action involving the 

 transformation of potential energy through palpable motion into 

 heat, than to a single finite mechanism, running down like a clock 

 and stopping for ever. It is also impossible to conceive either the 

 beginning or the continuance of life without a creating and over- 

 ruling power. The author's object w r as to lay before the Section 

 an application of these general views to the discovery of probable 

 limits to the periods of time past and future, during which the sun 

 can be reckoned on as a source of heat and light. The subject was 

 divided under two heads : 1, on the secular cooling of the sun; 2, 

 on the origin and total amount of the sun's heat. 



In the first part it is shown that the sun is probably an incan- 

 descent liquid mass radiating away heat without any appreciable 

 compensation by the influx of meteoric matter. The rate at which 

 heat is radiated from the sun has been measured by Herschel and 

 Pouillet independently ; and, according to their results, the author 

 estimates that if the mean specific heat of the sun were the same as 

 that of liquid water, his temperature would be lowered by 1°'4 Cen- 

 tigrade annually. In considering what the sun's specific heat may 

 actually be, the author first remarks that there are excellent reasons 

 for believing that his substance is very much like the earth's. For 

 the last eight or nine years, Stokes's principles of solar and stellar 

 chemistry have been taught in the public lectures on natural philo- 



* Communicated by the author, having been read at the Meeting of the 

 British Association at Manchester, September 1861. 



