340 FKAGMENTS OF SCIENCE. 



scientific literature has as yet brought to light a claim 

 which can sensibly affect the positions accorded to two 

 great Path-hewers, as the Germans call them, whose 

 names in relation to this subject are linked in indis- 

 soluble association. These names are Julius Eobert 

 Mayer and James Prescott Joule. 



In his essay on ' Circles ' Mr. Emerson, if I re- 

 member rightly, pictured intellectual progress as 

 rhythmic. At a given moment knowledge is surrounded 

 by a barrier which marks its limit. It gradually 

 gathers clearness and strength until by-and-by some 

 thinker of exceptional power bursts the barrier and wins 

 a wider circle, within which thought once more en- 

 trenches itself. But the internal force again accumu- 

 lates, the new barrier is in its turn broken, and the 

 mind finds itself surrounded by a still wider horizon. 

 Thus, according to Emerson, knowledge spreads by 

 intermittent victories instead of progressing at a uni- 

 form rate. 



When Dr. Joule first proved that a weight of one 

 pound, falling through a height of seven hundred and 

 seventy-two feet, generated an amount of heat compe- 

 tent to warm a pound of water one degree Fahrenheit, 

 and that in lifting the weight so much heat exactly 

 disappeared, he broke an Emersonian ' circle,' releasing 

 by the act an amount of scientific energy which rapidly 

 overran a vast domain, and embodied itself in the great 

 doctrine known as the ' Conservation of Energy.' This 

 doctrine recognises in the material universe a constant 

 sum of power made up of items among which the most 

 Protean fluctuations are incessantly going on. It is as 

 if the body of Nature were alive, the thrill and inter- 

 change of its energies resembling those of an organism. 

 The parts of the ' stupendous whole ' shift and change, 

 augment and diminish, appear and disappear, while the 



