Johns Hopkins University

Baltimore, November 23, 1894.

My Dear Mendenhall:-

I have carefully read your letter to Professor Marsh and think your view quite natural in many respects. But I will now give the facts of the case from my point of view and hope you will then see the matter as I do and join the Committee in a harmonious report on the subject.

The subject of electrical units as an international one, was started, as you know, at the Paris Congress in 1881 (I believe). The delegates to that Congress and all the succeeding ones included Barker, Trowbridge and myself. We had all attended one or more of these Congresses and taken a somewhat active part in them, having experimented for years on the Ohm and having refused to sanction 106. Cm. of mercury for the ohm from the first, always pleading for a higher number.

This Committee or delegation from the U. S. Government has never been changed and we have only lately handed in our report on the ohm.

When the Congress at Chicago was projected and I was called on to vote for the delegates, I stated this fact to Professor Gray and said that these persons were already the representatives of the United States, and suggested that he add two other names, one of which was yours, to this delegation.

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When he announced the Committee, ignoring these facts, and
leaving Barker and Trowbridge's names out, I was very indignant
and felt very much like resigning altogether. Indeed I believe
I wrote the letter, but did not send it.

At last I thought it better not to resign because we all
know how loose the methods are in this country. We have no oc-
casion to think that the best men will ever be appointed. It
is altogether a haphazard affair, and one could not expect any-
thing better from Professor Gray.

For the sake of peace I did not resign, although I some-
times think even now that I should have done so. I preferred to
accept the facts and do the best I could under the circumstances
to make the Chicago Congress a success.

But the Chicago Congress was a more form. The work had
been already done, and all nations had finally come around to
our (Barker's, Trowbridge's, and my) point of view. It was an
outrage that Barker and Trowbridge were not there. However, the
new delegation met those of other nations, and put the conclu-
sions in proper words, - nothing more.

Their work was then done and the delegation passed into
history. It was understood that you, as Superintendent of the
Coast Survey, would see to the passage of the law through Con-
gress.

The Committee, Helmholtz, Ayrton and Carhart, have never

reported. They have neglected their duty, however unavoidable
the cause.

In whatever manner it was accomplished, Congress has re-
ferred the matter to its advisers in such matters, the National
Academy of Sciences, to fill in the gap caused by the failure of
this Committee. The delegation to Chicago has nothing to do with
this matter: it belonged to the international Committee.

Had the United States Government been sufficiently intel-
ligent in such matters, they would have called on the National
Academy in the beginning.

Had Professor Marsh appointed the Committee as you sug-
gested, Trowbridge's name would have been left out. As it is,
he has returned to the original delegation, Barker, Trowbridge,
and myself, and added others so as to make the Committee as
national as possible.

In doing this I do not think the slightest disrespect can
be intended to Carhart or others. The Committee can ask these
gentlemen for their views in the matter, but otherwise it seems
as if their duties in the matter had ended with the Congress and
with their failure to report.

The matter is mostly formal as you know. If you will do
as I did and smother your feelings for the good of your country,
it is not yet too late, for your name is still on the Committee.
If you do otherwise it will cause more or less scandal of no

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good to anybody: for I do not see how the matter can now be
changed. Things in this world, especially in this country do
not always move smoothly and I hope you will not be the one to
roughen the way. The matter is unfortunate but I do not believe
Carhart or Thomson would expect, for a moment, to be put on a
Committee of the National Academy, unless it was suggested to
them.

Unless I hear from you to the contrary I shall consider
you as a member of the Committee, as we need your help and in-
fluence.

Baltimore, January 6th, 1895.

Dear Sir:-

At the Electrical Congress held at Chicago in
the Summer of 1893, the work of establishing an international sys-
tem of electrical units, commenced at the Paris Congress in 1881,
was concluded, and an international agreement was reached as to
the values of the Ohm, Ampere, Volt, Coulomb, Farad, Joule, Watt
and Henry.

This agreement was unanimous, without any dissenting
voice, and the delegates of the different governments separated
with the understanding that each delegation was to present the
report to its government with a view to have the units legalized by
proper legislation.

In accordance with this advice, the Congress of the
United States at its last session, passed laws to this effect de-
fining these units, so that they are to-day the law of this
country. But the law could not be made complete owing to the
fact that the International Committee appointed at Chicago to de-
fine the precautions necessary in obtaining the ampere and volt
by chemical means, never made its report. This Committee was
composed of Helmholtz of Germany, Ayrton of England and Carhart of
the United States, and the failure to report was probably due to
the ill health and death of Helmholtz before the report could be
made.

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It is to fill the gap made by the absence of this re-
port that the matter has been referred to the National Academy
of Sciences.

Our Committee, then, is to draw up specifications for the
determination of the ampere and volt by chemical means. But even
here we are not left in perfect freedom for the law goes so far
in either case that we are much limited in the scope of our in-
quiry. Thus, the ampere is defined for practical use as the
current which will deposit .001118 grams of silver per second
according to *standard specifications*, and the volt as the 1000/th
part of the electromotive force of a Clark cell at 15° C., pre-
pared according to *standard specifications*.

We have, then, only to define the means and precautions
necessary to deposit silver at the rate of .001118 grams per
second, leaving out all consideration of whether silver is the
best material or the figure .001118 is correct.

In the same way with the volt. The Clark cell may not
be the best but we have nothing to do with that. We have only
to inquire how a Clark cell must be made to give 1.434 volts at
15° C.

Evidently the best way to answer these inquiries is to
consult the scientific papers of those whose experiments have
given the results here stated.

Fortunately, I believe the experiments are so concordant

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that there is no dispute about the matter and we have thus only
to draw up the specifications in accordance with these experi-
ments.

Should any further experiment be made which varies at
all from these results now at hand, it would necessitate a new
Congress to again take into account the new results and change
the laws of all nations in accord with them.

Therefore I believe that it will be best for me to draw
up provisional specifications to be criticised by the Committee
and possibly serve as the basis of our report to the National
Academy of Sciences.

If this is agreeable to you I would be much obliged if
you would signify your consent.

Chairman of Committee
of
National Academy of Sciences