Suspension of the Magnetic Needle. 89 
of those who are desirous of making further improvements 
in the science of magnetism. In fig. 2. A is the bottom of 
the instrument, inches square, and one inch thick, to lie 
horizontally on the table, and made of mahogany. B B is a 
frame of the same wood, standing vertically on the middle of 
the square bottom, 6 j inches high, and 5- broad. On one 
side of the frame a piece of glass is fixed, and a piece of writing 
paper, gold beater's skin, or other thin substance, is pasted to 
the edge of the frame on the other side, so that the glass and 
the paper stand vertically and parallel to each other, at the 
distance of about half an inch, which is sufficient room for the 
needle, hanging by a spider's thread from the screw at C, 
which screw passes through the top piece D, which drops into 
an opening cut through the frame, and may be taken out by 
means of the knob of the screw at E. About 10 degrees of 
a circle are marked upon a bit of ivory fastened to the edge of 
the frame at F, and the needle, three inches long, is made of the 
smallest steel harpsichord wire, and is suspended by a spider's 
thread, also three inches long. A small tapering hair, fastened 
to the north pole with varnish, and extending about f of an 
inch farther than the end of the wire, points at the degrees on 
the ivory, so that its motion may be very accurately distin- 
guished, and especially by the use of a lens. Round the middle 
of the needle a small gold wire is twisted, and its end stand- 
ing perpendicularly is fastened to the spider's thread, to keep 
the needle in a horizontal position. 
The method of obtaining and fastening the spider's thread, 
which I have used, is this : — I take a forked stick, consisting of 
a stem and two or three branches, standing at about six inches 
asunder at their ends, and after finding a proper thread, in the 
MDCCXCII, N 
