510 FIRST REPORT UPON MAGNETIC WORK

allowed to project about 5 inches above the surface. In the centre of
each was leaded, flush with the top, a brass dowel one inch in diameter
and three inches long. The line was marked by crosses cut in the
brass dowels. The tops of the monuments contained some suitable
lettering, as for example:

North Monument or Meridian, 1807.

Owing to the lay and character of the grounds about the court-
houses¹ it was not always possible to plant the monuments on a true
north and south line. Of course any line whose true bearing is
known will suffice for the surveyor's purpose. It was my endeavor,
however, always to select as simple a line as possible. Thus at Fred-
erick (Frederick), Salisbury (Wicomico), Towson (Baltimore) and
La Plata (Charles) north and south lines were given; at Bel Air (Har-
ford) and Chestertown (Kent), northeast and southwest lines; at Cam-
bridge (Dorchester), a northwest and southeast line; at Centreville
(Queen Anne's), an east-southeast and west-northwest line, and at
Easton (Talbot), an east and west line.

After the line was established careful determinations of the mag-
netic declination, or variation of the compass, were made by me over
the monuments with the Coast and Geodetic Survey magnetometer.
The surveyor, hence, in addition to obtaining a line whose true bear-
ing was known, also had the privilege of having determined for him
the magnetic bearing with an instrument especially adapted for the
purpose. This accurate magnetic bearing gave him the means of
determining the reliability of his own instrument and of obtaining
the correction to be applied.

When the conditions were such that it was not possible to get

¹ The law prescribes that the line shall be established on some public
lot adjacent to the Court House.