600 FRAGMENTS OF SCIENCE. 
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 sensihly affect the 
positions accorded to two great Path-hewers, as the 
Germans call them, whose names in relation to this subject 
are linked in indissoluble association. These names are 
Julius Robert 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. I3ut 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 intermittent 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 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 " Con- 
servation of Energy." This doctrine recognizes 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 interchange 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 total of which they are the parts 
remains quantitatively immutable. Immutable, because 
when change occurs it is always polar plus accompanies 
minus, gain accompanies loss, no item varying in the 
slightest degree withqj.it an absolutely equal change of 
some other item in the opposite direction. 
The sun warms the tropical ocean, converting a portion 
of its liquid into vapor, which rises in the air and is 
recoudeused on mountain heights, returning in rivers to 
