the discovery of diamagnetism, of the influence of crystalline
structure on magnetism, and the completion of the mathematical theory
of electricity, all belong to the present epoch. To it also appertain
the practical execution and the working out of the results of the
great international system of observations on terrestrial magnetism,
suggested by Humboldt in 1836; and the invention of instruments of
infinite delicacy and precision for the quantitative determination of
electrical phenomena. The voltaic battery has received vast
improvements; while the invention of magneto-electric engines and of
improved means of producing ordinary electricity has provided sources
of electrical energy vastly superior to any before extant in power,
and far more convenient for use.

It is perhaps this branch of physical science which may claim the palm
for its practical fruits, no less than for the aid which it has
furnished to the investigation of other parts of the field of physical
science. The idea of the practicability of establishing a
communication between distant points, by means of electricity, could
hardly fail to have simmered in the minds of ingenious men since,
well nigh a century ago, experimental proof was given that electric
disturbances could be propagated through a wire twelve thousand feet
long. Various methods of carrying the suggestion into practice had
been carried out with some degree of success; but the system of
electric telegraphy, which, at the present time, brings all parts of
the civilised world within a few minutes of one another, originated
only about the commencement of the epoch under consideration. In its
influence on the course of human affairs, this invention takes its
place beside that of gunpowder, which tended to abolish the physical
inequalities of fighting men; of printing, which tended to destroy the
effect of inequalities in wealth among learning men; of steam