The prison mirror. [volume] (Stillwater, Minn.) 1887-1894, 1890-11-06
REPORT FOR DIVISION K.
MAGNETISM.


Magnetism is said to have derived its name
from the city of Magnesia, where the lodestOne,
or natural magnet. was first discovered by the
Greeks, and is the power which the magnet has to
attract iron and other magnetic bodies. An arti-
fetal magnet is straight or bent bars of tempered
steel that have acquired properties like those of
the lOdestone either by the action of other mag
nets or by galvanism. The attractive power Of
the magnet is not at all in the middle in fact for
some distance either side of the middle there
is absence of force; but its intensity increases
towards the ends. termed the poles. There is a
striking dissmiiarity in the poles. however, for
if magnet be suspended to swing freely
when it takes up fixed position one end will
keep to the north and the other to the south; and
the north pole cannot be made to stand a south
pole, and vice versa. Yet. if another magnet is
held near the suspended magnet. it will be dis
covered that the south pole of one attracts the
north pole and repels the south pole of the other.
1t is thus discovered that each magnet has north
and south pole, possessed of the same power in
attracting iron, etc., but differing in their action
on the poles of another magnet like poles re-
polling and unlike poles attracting each other.
The directive power of the magnet not dis
covered in Europe till the latter part of the 18th
century. But the Chinese emperor. Houangti. is
said to have invented an instrument for indicat-
ing the south in the year 1884 B. C. Unjust have
been used exclusively for land purposes till the year
300 A. d. that is the earliest date given for its
use at sea. The magnetic needle which is the es-
sential part of the compass does not exactly, in
most places, point directly north and south, but
with detection which varies from time to time in
magnitude, and may be towards the west or the
east. THE line of no variation in the United
States,'' given in text book. "passes near
Wilmington, N. c., Charlottesville, Va, and
Pittsburg, Penn"
\ will not enter into any further remarks on the
laws of magnetism. but will conclude with con-
densed description OF the compass as given in
Chambers's Encyclopedia:
The construction of compass depends entirely
upon the purpose it is to serve. For a mariners
compass the needle is fixed to circular card on
which there is star of 80 rays. indicating the 80
points of the heavens, and the card moves with
the needle which is placed in cylindrical brass
box and suspended by contrivance of gimbals in
such manner as to enable the compass to remain
horizontal in all positions of the ship. The whole
is then placed in a box called the pinnacle. In.
side the box in the direction of the ships bow, is
vertical black line, and the steersman must
keep the point of the card which marks the pre-.
scribed course always in contact with the black
line. Compasses differing in some respects from
the mariners compass also used in surveying
and land measuring; and for the miner they are.
perhaps. as necessary for the sailor.
"All Watches are Compasses. was the heading of
an article l read recently in one of the THE MIR
RORS exchanges. 1t was to the effect that bv
pointing the hour hand to the sum- the south
could be ascertaned by taking the figure half way
between the hour and the figure IL on the watch
"FOr instance, suppose that it is O'Clock; point
the hand indicating to the sun and on the
watch is exactly south. Suppose that it is
O'Clock; point the hand indicating to the sum-
and the figure 10 on the watch is due SOUTH
This appears to be modern discovery, that is
not generally known, for. as the writer, says:
Happening to meet Mr.. Stanley, 1 asked that
eminent traveller whether he was aware Of this
simple mode of discovering the points of the
compass, and he said that he had never heard of
it." Probably the world is in the same state of
ignorance.