xxvi
INTRODUCTION
reap such a rich harvest. Nearly five years before he had
carried out his investigation " On Electric Radiation" we find
in his day-book the notable remark-" 27th January 1884.
Thought about electromagnetic rays," and again, "Reflected on
the electromagnetic theory of light." He was always full of
schemes for investigations, and never liked to be without some
experimental work. So he did his best to fit up in his house
a small laboratory with home-made apparatus, thus transport-
ing himself back to the times when chemists worked with the
modest spirit-lamp. But before his experiments were con-
cluded or any of his schemes carried out he was called to
Karlsruhe, and his removal thither relieved him from much
unprofitable exertion caused by the lack of proper experimental
facilities.
This brings us to the end of the series of papers around
which we have grouped the events of the author's life. After
this follow the great electrical investigations which now form
the second volume of his collected works. At this point we
have introduced the lecture which Hertz gave at Heidelberg on
these discoveries, and which will still be fresh in the remem-
brance of many who heard it.
After this follows the last experimental investigation
which Hertz made. Whilst his colleagues, and in Bonn his
pupils as well, were eagerly pushing forward into the country
which he had opened up, he returned to the study of electric
discharges in gases, which had interested him before. Again
he was rewarded by an immediate and unexpected discovery.
Early in the summer-semester of 1891 he found that cathode
rays could pass through metals. The investigation was soon
interrupted, but was published early in the ensuing year; from
now on the subject-matter of his last work, the Principles
of Mechanics, wholly absorbed his attention.