466 FIRST REPORT UPON MAGNETIC WORK

and the present time the needle bore west all the time and did not at
any time point due north or east of north as surveyors frequently
assume to be the case for this part of Maryland. Looking over the
figures we find that at Baltimore the compass needle pointed about
6° 06' west in 1670 and that in about 1802 it pointed the least amount
west, namely, 39'; hence, in an interval of 132 years, the needle
changed its direction by 5° 27'. A street a mile long laid out in
Baltimore in 1670 so as to run parallel to the compass direction would
have its north terminus 504 feet, or about 1/10 of a mile, too far to the
west in 1802! This is a fact especially interesting because in some
of the old towns of Maryland the streets were laid out by the compass,
or prominent public buildings, such as court houses, erected so that
the front face would run paralled to a cardinal direction as given by
the compass. For example, while establishing a meridian line for the
use of surveyors at Chestertown, the county-seat of Kent county, I
found that High street, the main street, ran very nearly magnetically
northwest and southeast. Assuming that the street was originally
laid out with the compass so as to run northwest and southeast, and
knowing from the data at Baltimore and some other stations that the
needle bore the same amount west in the early part of the eighteenth
century that it does at present, the conclusion to be drawn was that
the town of Chestertown was laid out in the early part of the last
century. Upon looking up the records, the assumptions made and
the conclusions drawn were verified. The town was laid out in 1702
and the streets run with the compass northwest and southeast and at
right angles thereto.

The table likewise gives the change in the compass direction at some
stations in the Southern Hemisphere. One fact at once noticeable
from this table is, that during a given interval of time the compass
direction changes not only by different amounts in different parts of
the earth, but, likewise, the changes occur in some parts in opposite
directions. Let us compare, for example, the changes which have
occurred between 1800 and 1890 at the various stations.