113 



the law wKidi connects radiation and temperature. The difficulty 

 lies in the inability to test any empirical formula beyond about 

 4000° F., the limit to which bodies can be heated on this earth. 

 And yet, so far, the whole history of science declare that it would 

 be rash indeed to deny that the goal is attainable. 



8. How THE Heat of the Sun is maxntained. 

 The most probable opinion of the mode in which the heat of 

 the sun is maintained, is the contraction theory of Helmholtz. 

 Gravity tends to push the outer parts of the sun towards the centre, 

 heat tends to make the mass expand and drive these same parts 

 away from the centre. But the balance is ultimately in favour of the 

 contracting force, the equihbrium being disturbed by the loss of 

 heat consequent on radiation at the free surface. But if the sun 

 contracts, work is being done, for a resistance is being overcome, 

 and work done has an exact equivalent in heat. And so the heat 

 thus generated by contraction continually supplies the place of 

 that which has been lost by radiation into space, and which has 

 given both light and heat to the planetary spheres. It has been 

 computed that in order to furnish heat sufficient for the present 

 rate of solar expenditure, the contraction demanded is one mile 

 in 25 years, or four miles in a century. Such a diminution in 

 the sun's radius could not be observed in less than ten thousand 

 years, so that the theory cannot be tested by actual observation. 

 However, it follows immediately from the doctrines of the con- 

 servation of energy, and of the mechanical equivalent of heat. 

 It receives stray confirmation from the study of the nebulae ; for 

 the-spectrum of a nebula is a gaseous spectrum, and the telescope 

 shows nebulae in the heavens in all stages of condensation. In 

 fact the theory is but a modification of Laplace's famous nebular 

 hypothesis, to which it tends additional weight. Finally, an 

 interesting point, this hypothesis gives 20,000,000 years as the 

 past life of the sun, and would allow not more than between five 

 and six miUion years of sunlight in the future. 



THE EVOLUTION OF EAST LANCASHIRE 

 BOGGARTS. 



By JAMES Mc KAY. November 27th, 1888. 



Most people who have attained to so much as middle age, if 

 they are natives of East Lancashire, can well remember that in 

 their young days there were particular spots about their homes 



