INTRODUCTION
xxiii
20th September 1882.
The battery has practically been ready since the middle of last
week; since last Sunday night it has begun to spit fire and light
up electric tubes. To-day for the first time I have made experi-
ments with it-ones which I couldn't have carried out without it.
7th October 1882.
I have got the battery to work satisfactorily, and a week ago
succeeded in solving, to the best of my belief, the first problem
which I had propounded to myself (a problem solved, when it
really is solved, is a good deal!). But even this first stage was
only attained with much trouble, for the battery turned sick, and
its sickness has proved to be a very dangerous one.
By preventive measures the battery was kept going for
yet a little while, and later on he reports, "Battery doing
well." How the battery finally came to grief is explained
in the account of the investigation (XIII.) By its aid he was
able, in six weeks of vigorous exertion, to bring to a success-
ful issue most of the experiments which he had planned out.
The investigation was first published in April 1883 at Kiel,
in connection with Hertz's induction to the position of Privat-
docent there. It brought him recognition from one who
rarely bestowed such tokens, and whose opinion he valued
most highly. Hertz treasured as precious mementoes two
letters from Helmholtz. One of these notified his appoint-
ment as assistant at Berlin; the other is the following:-
BERLIN, 29th July 1883.
GEEHRTER HERR DOKTOR!-I have read with the greatest
interest your investigation on the cathode discharge, and cannot
refrain from writing to say Bravo! The subject seems to me to
be one of very wide importance. For some time I have been
thinking whether the cathode rays may not be a mode of pro-
pagation of a sudden impact upon the Maxwellian electromagnetic
ether, in which the surface of the electrode forms the first wave-
surface. For, as far as I can see, such a wave should be pro-
pagated just as these rays are. In this case deviation of the
rays through a magnetisation of the medium would also be
possible. Longitudinal waves could be more easily conceived;
and these could exist if the constant k in my electromagnetic
researches were not zero. But transversal waves could also be