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Ans Dec 18

Office Lake Survey, Detroit, Mich.
Dec. 13th, 1871

Dr. I. A. Lapham
Milwaukee, Wis.

Dear Sir:

Yours of Dec. 4th and also comparisons of Chicago and
Milwaukee water levels by means of curves have been
received. These were very useful to me in sug-
gesting where the former reductions may have been wrong.

The tracing from the curves you sent me herewith enclosed
as corrected from the published repot of 1870 will I trust
be quite satisfactory to you.

I enclose also a copy of results as requested by you.

The correction of one foot has already been applied so that
you need to subtract from 4.00 and not from 5.00. This
reduction will make the curves for 1870 & 1871 harmonize
more nearly with other years.

In the year 1866 the Self Register must have been near the Light
house and in the month of August it was upset by a vessel.
The staff gauge immediately afterwards read larger.
Was the zero of this staff gauge also disturbed?
When was the gauge moved to the canal?

[begin crossed out] Was it then as when established by Gen. Meade just
1 ft above High Water of 1838? Is it now at the same level as
when established by Gen. Meade? Has it always been [end crossed out]

I see that you answered me these questions before