dict their recurrence, as far as they
depend upon the forces which have been mentioned? A knowledge of the
laws of the cycles through which these forces pass is the first and
only step in this direction to be taken, and this step must be made by
patient, long-continued observations."

[Illustration: PROFESSOR T. C. MENDENHALL.]

An immediate practical use of the observations to be made is their
application to the correction of compass errors. Every one can see
that such work as tends to render the mariner's compass a more
reliable instrument must be of immediate and direct benefit, not only
to the sailor, but to the surveyor on land.

Admitting that the observations of such an expedition as that to the
North Magnetic Pole will be of scientific and general value, it
remains to explain something of the personnel of the party, how the
work is to be conducted, and by what route it will reach the field of
its labor.

Besides the two observers of terrestrial magnetism to be supplied by
the Coast Survey, there will be a physician fitted by education and
habits of study to take charge of some scientific portion of the work,
in which he will be specially instructed by the Superintendent of the
Coast Survey or his assistant. There will also be three sailors
selected from the whaling fleet, who will have charge of the three
whale boats belonging to the outfit, and act as assistants to the
several observers. The writer of this article, by reason of his
experience in Arctic travel, will have charge of the expedition in all
except the scientific work, the reports on which will be turned over
directly to the officers of the United States Coast and Geodetic
Survey for reduction and discussion upon the return of the party from
the field.

The scheme of work has already been prepared by Professor Charles A.
Schott, who is looked upon as probably the best informed on all the
details of terrestrial magnetism of all men in this or any other
country. In the course of his exhaustive report upon this subject he
says: "The magnetic observations proper will comprise the measure of
the three elements, the declination, the dip, and the intensity, which
fully define the magnetic force at a place. The measures will be
partly absolute and partly differential, and will be considered under
two heads; those to be taken while travelling, and those to be
attended to at winter quarters." Detailed instructions for this work
are given which are too te