xiv
INTRODUCTION
whereas only about half a year ago I scarcely knew any more
about it than what still remained in my memory since the time
when I was with Dr. Lange. I hope my work won't suffer from
this. At present it looks promising. I have already surmounted
the difficulties which Helmholtz pointed out to me at the start as
being the principal ones; and in a fortnight, if all goes well, I
shall be ready with a scanty kind of solution, and shall still have
time left to work it up properly.
He asks his parents to send on a tangent galvanometer
which he had made during the last holidays at home, without
having any suspicion that it would so soon be used in this
way.2
A week later, in writing to report progress, he is not so
cheerful. "When one difficulty is overcome, a bigger one
turns up in its place." These were the difficulties mentioned
in pp. 5-6. The Christmas holidays were now at hand, and
while at home in Hamburg he made the commutator shown
on Fig. 1, p. 13, respecting which he later on reports.
12th January 1879.
The apparatus which I made works very well, even better than
I had expected; so that within the last three days I have been able
to make all my measurements over again, and more accurately than
before.
Within three months after he had first turned his atten-
tion to this investigation he is able to report the conclusion of
the first part of it.
21st January 1879.
Then
It has delighted me greatly to find that my observations are in
accordance with the theory, and all the more because the agree-
ment is better than I had expected. At first my calculations gave
a value which was much greater than the observed value.
I happened to notice that it was just twice as great. After a long
search amongst the calculations I came upon a 2 which had
been forgotten, and then both agreed better than I could have
expected. I have now set about making more accurate observa-
1 The Head-Master of the Bürgerschule, which he attended up to his six-
teenth year.
2 This is the galvanometer referred to on p. 12 (3)—a simple wooden disc
turned upon the lathe and wound with copper wire, with a hole in the centre
for the magnet. It is still in good order.
1