416 THE WORLD MACHINE 



forces may vary in their manifestations ; no whit of their energy 

 is ever lost. 



This vast idea of the correlation of forces or, as we say 

 now, of the conservation of energy came as a veritable dis- 

 covery. Like many a discovery like, it might be said, nearly 

 all great discoveries it was reached independently and simul- 

 taneously by several different minds. One of these was a rich 

 brewer's son in England, James Fresco tt Joule ; a second was 

 Colding, a Dane ; a third was Julius Robert Mayer, an obscure 

 physician of Heilbronn in Germany ; a fourth was a young 

 military physician of Berlin, Hermann von Helmholtz. The 

 formulation of this law was in many ways the highest flight 

 of the nineteenth-century mind. 



The papers in which this discovery was enunciated were 

 published, each in unconsciousness of any other, between the 

 years 1842 and 1847. The force of their tremendous import 

 was not immediately felt. It was fifteen or twenty years before 

 it seemed of enough consequence to squabble about who reached 

 the idea first. But in the meantime one of its discoverers had 

 seen its bearing upon the most important outlying problem 

 in physical astronomy, and turned his attention thereto. This 

 was the source of the sun's heat. It had long been a puzzle. 

 Sir John Herschel styled it " the great secret." 



Long before this time the development of geology, the re- 

 velations of the rocks, had made it. clear that our earth had 

 existed for aeons of time. Compared with it, the hypothetical 

 date of the creation of the world did not represent the stroke 

 of a second in the movements of a clock. Throughout millions 

 upon millions of years the sun had been pouring downwards 

 upon this ancient earth, and outwards through space, its floods 

 of light and heat. Whence came this colossal store ; how 

 could it thus seemingly go on for ever without diminution ? 

 This was the problem, and no one could answer. 



The first to make any rational attempt was the obscure 

 Heilbronn physician. Convinced by his studies that some sort 

 of source must be found, unable to discover it in the sun itself, 

 he thought to find it in the incessant rain of meteors upon the 

 sun's face. Simple observation of the heavens had shown him 

 that the number of meteorites pouring nightly and daily into 

 the atmosphere of the earth was enormous. In the deep cold 



