MARYLAND GEOLOGICAL SURVEY 413

subject of the secular variation so much attention from the purely
practical standpoint, as in this country. All the earlier surveys were
referred to the magnetic meridian instead of the true meridian. And
since in but very few cases the deviation of the magnetic meridian
from the true one was determined by the early surveyor, it becomes a
practical problem to know how much allowance shall be made for the
shifting of the reference meridian of the early survey in order that
the " metes and bounds " of the original plat can be re-located at some
future date. One of the Eastern states is still so far behind the times
as to recognize on its statute-book the magnetic meridian as the
meridian of reference for land surveys! Even in Maryland no sys-
tematic effort has been made by the state to put the matter of its land
surveying on a practical and scientific basis, so as to prevent costly and
annoying litigations as far as possible in the future.

We are now acquainted with two of the practical objects of a
magnetic survey:

a. The determination of the angle between the true north 'and
south line and the magnetic north and south line.

b. The determination of the angle by which the magnetic meridian
has shifted its direction during given intervals of time.

The accomplishment of these two objects suffices for the practical
needs of the surveyor. The prosecution of a magnetic survey along
these lines alone, however, will never materially advance our knowl-
edge of the laws underlying and controlling the secular variation.
There are, namely, other manifestations of the earth's magnetic force
which demand recognition if we desire to make continued progress in
the hope of being able ultimately to improve and perfect the laws
which at present must be wholly empirical.

THE MAGNETIC INCLINATION.

In the year 1576 a London mathematical instrument maker, Robert
Norman, made the following important discovery, the account of which
I shall give in his own words: ¹

¹ Quoted from his book: The New Attractive shewing the Nature, Prop-
ertie, and manifold Vertues of the Loadstone with the Declination of the
Needle touched therewith under the Plaine of the Horizon, found out and