Date.

OBSERVATIONS OF MINIMUM TEMPERATURE DURING THE NIGHT. Spirit thermometer, having a steel index within the tube.

Observed minimum

temperature.

Thermometer

re

duced to open-air

dry thermometer.

For decrease of gravity on a vertical acting on the mercurial column.
For decrease of gravity on a vertical acting on the density of the air.
For atmospheric humidity...

Height of Fort Yukon above Redoubt St. Michael's.
Estimated height of Redoubt St. Michael's above the level of the sea..

Approximate height of Fort Yukon above the level of the sea..

350.4 ±4.9

+20.7

-00.6
+00. 12
00.0
+ 1.4

372.0 ±4.9
40.0

412.0

OTHE

Special Session. S

LETTER

OF

No. 1.

THE

SECRETARY OF WAR,

COMMUNICATING,

In compliance with the resolution of the Senate of the 15th instant, the report of a board of engineers appointed to examine and report upon bridges across the Ohio River.

MAY 17, 1871.-Ordered to lie on the table and be printed.

WAR DEPARTMENT, May 16, 1871.

The Secretary of War has the honor to transmit to the United States Senate, in obedience to a resolution of the 15th instant, the final report of a board of engineers, appointed under authority of law, to examine and report upon bridges across the Ohio River.

WM. W. BELKNAP,
Secretary of War.

ENGINEER OFFICE UNITED STATES ARMY,
Newport, Rhode Island, April 19, 1871.

GENERAL: AS presiding officer of the board of engineers appointed under section 5 of the river and harbor improvement act, approved July 11, 1870, I transmit herewith our final report; and, in order to give it completeness, we have annexed to it, as appendices, our two preceding partial reports on the subject of bridging the Ohio River. In the part which forms our last report we have recommended a change to be made in but one bridge, viz, that near Steubenville. We are not positive as to whom the expense of making this change should be charged, and the question is one to which we think the attention of Congress should be solicited.

There has been not a little labor expended upon this report and the maps accompanying it, and the endeavor has been to make it as complete as possible in regard to the facts. A large part of this work has been executed by and under the direction of Brevet Colonel W. E. Merrill, and beside any merit that may attach to its execution he must be credited with a large abstraction of his time from the other engineering duties belonging to his station. We are also much indebted for the faithful and comprehensive surveys, measurements, and calculations to