30 INTRODUCTION

the determination at a number of points of the so-called magnetic ele-
ments, viz., the magnetic declination, the magnetic inclination or dip,
and the horizontal component of the earth's magnetic force. These
three elements completely determine the direction and intensity of
the magnetic force prevailing at the points of observation. In addition
to the far-reaching importance of this work in the future observations
and determinations of the great rock masses contained within the
state, the results will be of immediate practical benefit to all land
surveyors, and from that standpoint alone will more than justify the
undertaking.

The importance of magnetic surveys has been recognized for many
years, the first survey of this kind having been made in England in
1837. Magnetic surveys have also been made in several of the other
European countries, but little systematic investigation in this direc-
tion has as yet been undertaken in America. The State Geological
Survey intends to make a thorough and systematic magnetic survey of
Maryland, and this is to a large extent made possible by the fact that
the costly apparatus in the possession of the United States Coast and
Geodetic Survey has been placed at the disposal of the state. Already
much work has been done in the carrying out of the plan.

In this connection attention should be called to the fact that an
act of Assembly was passed at the session of 1870 (Laws of Maryland,
Chapter 359) arid codified in 1888 (Maryland Code, Article 25), in
which it is stated that " it shall be lawful for the county commissioners
of each county in the state, if they shall deem it expedient, to cause
to be erected on some public spot adjoining the court house of each
county two good and substantial stone pillars, 100 feet apart the one
from the other, and upon the same true meridian line. " Further
directions for the establishment of these pillars are given, together
with the provisions for their use by the surveyors in each county. As
a result of the work already done by the State Geological Survey,
combined with the fact that the necessary apparatus is at its disposal,
it is now possible for the several counties of the state at a very small
outlay to take advantage of this opportunity. Already several of the
counties have co-operated with the State Survey in the establishment