nowledge 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 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 '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 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 without
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 vapour, which rises in the air and is recondensed on mountain
heights, returning in rivers to the ocean from which it came. Up to
the point where condensation begins, an amount of heat exactly
equivalent to the molecular work of vaporisation and the mechanical
work of lifting the vapour to the mountain-tops has disappeared from
the universe. What is the gain corresponding to this loss? It will
seem when mentioned to be expressed in a foreign currency. The loss
is a loss of heat; the gain is a gain of distance, both as regards
masses and molecules. Water which was formerly at the sea-level has
been lifted to a position from which it can fall; molecules which have
been locked together as a liquid ar