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16 REPORT—1845. 
portional in all their dimensions, are not in the ratio of the masses, the large masses 
being less strong proportionally than the smaller. 4. That whilst magnets of large 
dimensions are less powerful with respect to their masses than small magnets to 
which they are exactly proportional in all their dimensions ; and whilst the increase 
of the dimensions continually deteriorates from the energy due to the mass; yet 
magnets may be combined in such proportional dimensions with a constant increase 
of power ad infinitum. From this last result, it follows that magnets indefinitely 
small must be indefinitely strong; and may indicate that the mutually attractive 
forces of the ultimate magnetic elements may be as strong as that’ by which the me- 
tallic elements are themselves combined. It must also be kept in mind that the 
steel should be perfectly hard; and the elementary plates of the magnet should be 
made of steel, converted out of one or other of the very best qualities of foreign iron. 
All the conditions, with the exception of thinness, were attended to in the large 
magnet constructed by Dr. Scoresby. A magnet on this principle, of the size of the 
lower mast of.a first-rate ship of war (which might be constructed of plates of very 
hard cast iron), would produce a deviation of nearly 1! at the distance of a mile, and 
a sensible effect much beyond that. The two fasciculi of Dr. Scoresby’s magnetical 
machine were about 4 feet in length each, 43 inches in breadth, and about 6 inches 
in depth. Nearly 600 running feet of steel, in 504 bars, were originally provided, 
weighing altogether 750 lbs.; but many were rejected, not being found hard enough 
to stand the magnetic test. The attractive force, though not a favourable arrange- 
ment for sustaining weight, was sufficient to carry 400 lbs. The inductive energy 
on iron bars or keys, held at 6 to 12 inches distance, was extraordinary, sufficient to 
sustain a chain of six keys of considerable size. With a deal board of 0-4 inch in- 
terposed betwixt the magnet and the conductor, a weight of 15 lbs. was sustained. 
The following electrical effects were produced by Dr. Scoresby’s magnet with a 
very imperfect armature. It decomposed water rapidly, producing about one cubic 
inch of the gases a minute; with about sixty-five yards of coiled wire, the effer- 
vescence seemed as violent as during the action of dilute sulphuric acid on zinc. 
Copper was deposited from a solution of sulphate of copper at the rate of about 1°2 
grains per minute. Shocks were powerful, and scintillations were thrown out; and 
sparks were visible in daylight, and emitted audible sounds when the armature re- 
volved so slowly as once in sixteen seconds.: 
On the Baron de Bode’s Insulated Compass. By Joszrpn York Otiver. 
The object was to insulate the compass from the action of the iron of the ship. 
The contrivance was this: a double glass bowi, the intermediate space being filled 
with mercury, was made to act as the bowl of the ordinary compass. It was hung 
in gymbals, and surrounded by lead for protection. The author remarked on the 
utility of employing a similar apparatus for securing chronometers from the local 
attraction of the iron on shipboard. 
On a Method of suspending a Ship's Compass. By E. J. Dent, F.R.A.S. 
An account of this instrument was communicated to the Association at its last 
meeting in York. Mr. Dent now read extracts from a report of the working of this 
compass during six months at sea, as ordered by the Lords of the Admiralty, to 
the effect that his compass was found ‘‘to be extremely sensitive, moving exactly 
and admirably with the ship’s head, when the helm was put hard-a-port and hard- 
a-starboard; while the other compasses with which it was compared were always 
in arrear.”” 
On the Connection between Magnetic Variation with certain peculiarities of the 
Earth's Structure. By S. M. Saxsy. 
Mr. Saxby was of opinion that it will be found, on examining the direction of the 
various mountain ridges of the globe, that there is a remarkable angular coincidence 
between such line of direction and the local curve of equal magnetic variation, the 
one crossing the other at angles of from 65° to 70°. ’ 
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