has been for some time in this city,
hard at work upon a compass Co make
it indicate its own variations, from
whatever cause they may proceed.—
And, at last, he has accomplished the
task. I have seen two large com pas
ses of his make, which tell with uner
ring precision, the <'fcact variation of
the needle to the East or the West,
whether from adhesion or repulsion,
whether from local, immediate, or dis
tant causes. The main needle is un
derneath the dial of the compass, while
on its face, at the Ea-t and West
points, are stationed two small needles
running about half way across the di
al. These, in whatever position the
compass may be placed, and no mat
ter what, large or small magnetic or
attractive bodies may be placed near
it or round about it, it will point East,
if the variation is that way, or West,
if it is the other way, the points of
each striking off from the other along
a circular strip of brass, which num
bers the distance. To ascertain the
true variation, the numbers marked by
the two needles arc added together,
and one-half of the amount shows the
number of degrees the compass varies
cither to the East or West, as the case
may be.
It is said that, in consequence of the
the officers not being able to ascertain
the variations of the compass, the
Great Britain has several times got out
of her true course, and run on rocks
and shoals.
Mr. St. John’scompasscs have been
thoroughly tested by the Navy De
partment, and approved, and I under
stand Mr. Secretary Mason has issued
an order for a given number of them
at 3100 each.
