p.1

Milwaukee Dec 4, 1871

Dr Sir

Upon reciept of your letter of the
2 I immediately set about finding whether
anything, and if so what is the matter
with my zero, and whether there is any
error in the reductions of the observation of the level of
the Lake at the Station. As I before
wrote you, a couple level run from an
original bench mark shows that there
has been no change in the mark used
here; and there can be no mistake in
measuring rod.

An examination of the table & curves herewith
sent suggest the idea that there may have
been since 1866, some misapprehension of the zero
adopted. That zero was established by
Capt. Meade exactly one foot above the high
water of 1838* and all my observations & reports are made with reference to this zero. [With?] the memorandum accompanying
you letter you say the plains of reference is
the high water of 1838, which, if correct,
* Report 1860 page 8.