can always be trusted to lead us on to further knowledge. We see it
working under known conditions, and relying on its unchangeableness, we
can then logically infer what it will do under other hypothetical
conditions, and in this way many important discoveries have been made.
For instance it was in this way that Mendeléef, the Russian chemist,
assumed the existence of three then unknown chemical elements, now
called Scandium, Gallium and Germanium. There was a gap in the orderly
sequence of the chemical elements, and relying on the old maxim--"Natura
nihil facit per saltum"--Nature nowhere leaves a gap to jump over--he
argued that if such elements did not exist they ought to, and so he
calculated what these elements ought to be like, giving their atomic
weight, chemical affinities, and the like; and when they were discovered
many years later they were found to answer exactly to his description.
He prophesied, not by guesswork, but by knowledge of the Law; and in
much the same way radium was discovered by Professor and Madame Curie.
In like manner Hertz was led to the discovery of the electro-magnetic
waves. The celebrated mathematician Clerk-Maxwell had calculated all
particulars of these waves twenty-five years before Hertz, on the basis
of these calculations, worked out his discovery. Again, Neptune, the
outermost known planet of our system was discovered by the astronomer
Galle in consequence of calculations made by Leverrier. Certain
variations in the movements of the planets were mathematically
unaccountable except on the hypothesis that some more remote planet
existed. Astronomers had faith in mathematics and the hypothetical
planet was found to be a reality. Instances of this kind might be
multiplied, but as the French say "à quoi bon?" I think these will be
sufficient to convince the reader that the invariable sequence of Law is
a factor to be relied upon, and that by studying its working under known
conditions we may get at least some measure of light on conditions which
are as yet unknown to us.