120 HISTORICAL SKETCH

were frequently made with the measured lines of wharves, piers and
docks, and the agreement left nothing to be desired in point of
accuracy.

In extending the survey along such parts of the shore as were not
occupied by wharves or piers, and which could not be clearly defined
otherwise, a leveling instrument was used to mark out the line of
mean high water. This plan was ascertained by the observation of a
series of day and night tides extending through two lunar months.
Tide stations were established at Henderson's wharf (Fell's Point),
Woodall's ship yard (Locust Point), Bollman's wharf (Canton), and
at Winans' dock in the Patapsco river. The series was recorded at
the Fell's Point gauge, and during intervals free from winds and
abnormal tides, simultaneous observations were made to determine
differences of period of maximum of flood and ebb. These differences
were found to be less than 15 minutes, or practically inappreciable in
the limited tidal flow of the harbor, which the mean of one hundred
and fifteen tides show to be 1. 16 feet, or. 04 feet less than that
established for the station at Fort Carroll. The sounding of the
harbor was begun early in October and continued without interruption
until that part of the area known as Spring Garden was closed by ice.

During the progress of hydrographic work the shores of the Patapsco
river on both sides were surveyed, scale 1: 3600 (300 feet to the inch).
The space between the head of the basin and the lines of Canton was
mapped on the scale of 1: 1800 (150 feet to the inch). The hydro-
graphic survey covered the entire area above the line of the Lazaretto
and Marine Hospital wharf, excepting the main branch of the river
above the Long Bridge. The area of the basin and harbor to the
entrance at Fort McHenry was sounded and plotted on the scale of
the topographical sheets that covered the same locality.

On June 1, 1877, the survey was resumed at Spring Garden and
in the Patapsco (main branch) between the drawbridge and Brooklyn,
west of the bridge.

The recorded details show that in the course of the survey 17, 400
soundings were made and 1443 angles measured for determining the
position of the boat while sounding in midwater. The positions at