on its proper place in the doctrine
of conservation. In the leaves of a tree, the carbon and oxygen of
carbonic acid, and the hydrogen and oxygen of water, are forced
asunder at the expense of the sun, and the amount of power thus
sacrificed is accurately restored by the combustion of the tree. The
heat and work potential in our coal strata are so much strength
withdrawn from the sun of former ages. Mayer lays the axe to the root
of the notions regarding 'vital force' which were prevalent when he
wrote. With the plain fact before us that in the absence of the solar
rays plants cannot perform the work of reduction, or generate chemical
tensions, it is, he contends, incredible that these tensions should be
caused by the mystic play of the vital force. Such an hypothesis
would cut off all investigation; it would land us in a chaos of
unbridled phantasy.

'I count,' he says, 'therefore, upon your agreement with me when I
state, as an axiomatic truth, that during vital processes the
conversion only, and never the creation of matter or force occurs.'

Having cleared his way through the vegetable world, as he had
previously done through inorganic nature, Mayer passes on to the other
organic kingdom. The physical forces collected by plants become the
property of animals. Animals consume vegetables, and cause them to
reunite with the atmospheric oxygen. Animal heat is thus produced;
and not only animal heat, but animal motion. There is no
indistinctness about Mayer here; he grasps his subject in all its
details, and reduces to figures the concomitants of muscular action. A
bowler who imparts to an 8-lb. ball a velocity of 30 feet, consumes
in the act one tenth of a grain of carbon. A man weighing 150 lbs,
who lifts his own body to a height of 8 feet, consumes in the act 1
grain of carbon. In climbing a mountain 10,000 feet high, the
consumption of the same man would be 2 oz. 4 drs. 50 grs. of carbon.
Boussingault had determined experimentally the addition to be made to
the food of horses when actively working, and Liebig had determined
the addition to be made to the food of men. Employing the mechanical
equivalent of heat, which he had previously calculated, Mayer proves
the additional food to be amply sufficient to cover the increased
oxidation.

But he does not content himself with showing, in a general way, that
the human body burns according to definite laws, when it performs
mechanical work. He seeks to