d. But it so happened that Picard
shortly afterward executed more correctly a new measurement of a degree;
this changed the estimated magnitude of the earth, and the distance of
the moon, which was measured in earth-semidiameters. Newton now renewed
his computation, and, as I have related on a previous page, as it drew
to a close, foreseeing that a coincidence was about to be established,
was so much agitated that he was obliged to ask a friend to complete it.
The hypothesis was sustained.

A second instance will sufficiently illustrate the method under
consideration. It is presented by the chemical theory of phlogiston.
Stahl, the author of this theory, asserted that there is a principle of
inflammability, to which he gave the name phlogiston, having the quality
of uniting with substances. Thus, when what we now term a metallic oxide
was united to it, a metal was produced; and, if the phlogiston were
withdrawn, the metal passed back into its earthy or oxidized state. On
this principle, then, the metals were compound bodies, earths combined
with phlogiston.

SCIENCE AND ECCLESIASTICISM. But during the eighteenth century the
balance was introduced as an instrument of chemical research. Now, if
the phlogistic hypothesis be true, it would follow that a metal should
be the heavier, its oxide the lighter body, for the former contains
something--phlogiston--that has been added to the latter. But, on
weighing a portion of any metal, and also the oxide producible from it,
the latter proves to be the heavier, and here the phlogistic hypothesis
fails. Still further, on continuing the investigation, it may be shown
that the oxide or calx, as it used to be called, has become heavier by
combining with one of the ingredients of the air.

To Lavoisier is usually attributed this test experiment; but the fact
that the weight of a metal increases by calcination was established
by earlier European experimenters, and, indeed, was well known to the
Arabian chemists. Lavoisier, however, was the first to recognize its
great importance. In his hands it produced a revolution in chemistry.

The abandonment of the phlogistic theory is an illustration of the
readiness with which scientific hypotheses are surrendered, when found
to be wanting in accordance with facts. Authority and tradition pass for
nothing. Every thing is settled by an appeal to Nature. It is assumed
that the answers she gives to a practical interrogation will ever be
true.