SCIENCE AND MAN 857 



in his dealings with scientific history keeps his soul un- 

 warped by envy, hatred, or malice, personal or national, 

 every fresh accession to historic knowledge must be wel- 

 come. For every new-comer of proved merit, more espe- 

 cially if that merit should have been previously over- 

 looked, he makes ready room in his recognition or his 

 reverence. But no retrospect of 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 sub- 

 ject are linked in indissoluble association. These names 

 are Julius Eobert Mayer and James Prescott Joule. 



In his essay on "Circles" Mr. Emerson, if I remember 

 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 entrenches itself. But the internal force again 

 accumulates, 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 inter- 

 mittent victories instead of progressing at a uniform 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 competent 

 to warm a pound of water one degree Fahrenheit, and 

 that in lifting the weight so much heat exactly disap- 

 peared, 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 doctrino 



