14 REPORT—1843. 
tions, if any particular case were stated, he could easily determine the requisite quali- 
ties. That the power of a magnet was essentially dependent on both quality and hard- 
ness, he, Dr. Scoresby, proceeded to show by experiment with four small bars of similar 
size, but of different qualities or tempers. One lifted only 600 grains, another about 
1000, another the same, another 3200 grains. Tried by Dr. Scoresby’s mode of testing 
described last year, he found the first to be bad in quality, the second inferior and too 
soft, the third good in quality but not hard enough, the last excellent in quality and 
hardness. In being in succession laid on the test bar, the first three lost all their 
power, whilst the last retained still the power of lifting a key of 3200 grains’ weight. 
Two anomalies in practical magnetism were then described. First, the experi- 
mentally determined fact, that proportional magnets of similar steel and temper were 
not energetic proportionally with their masses; in other words, that two magnets, one, 
for instance, being double in all its dimensions of the other, would not exhibit powers 
corresponding with their masses, or in proportion to the cubes of their lengths,—the 
proportions, instead of being as 13: 23= 8, would perhaps be found to be as 1 to 5 or 
6 only. Hence it would be inferred that magnets could not be advantageously en- 
larged to an indefinite extent: at the same time, from the experiments already made, 
he, Dr. Scoresby, would have no difficulty in constructing a magnet of a ton weight, 
and, by means of his peculiar test (which he had exhibited to the Section), of render- 
ing every bar effective. The other anomaly to which he referred was that arising out 
of difference of form. In all his experiments on more than 1000 bars or plates, he 
had always found that extreme hardness was the most effective in large or consider- 
able combinations of straight bar magnets. His surprise was therefore great on trying 
the same principle on two horse-shoe magnets of five and fifteen bars, to find that the 
same Taw did not prevail. The magnets, until reduced in temper, were of low power. 
To reduce them by a fixed and determinate rule, he, Dr. Scoresby, adopted a bath of 
oil boiling at about 600°. He tried the effect of various temperatures, from 300° to 
the boiling, and thence determined the ratio of improvement until he obtained the 
best. The magnets annealed ultimately at an uniform temperature of 505°, now ex 
hibited very superior powers, lifting from seven to nine times their own weight, 
Description of a Galvanometer. By J. P. Jour. 
It is a well-established principle in electro-dynamics, that if a small magnetic needle 
be suspended in the centre of a coil or helix, and in the plane of its axis, the tangents 
of its deflections will be nearly, but not exactly, proportional to the quantity of cur- 
rent passing through the; coil. It has therefore been found necessary to construct 
tables for turning the deflections of the needle into quantities of current. The ne- 
cessity of forming these tables was first insisted upon by M. Becquerel; and in his 
treatise on Electricity he has pointed out the laborious experimental processes employed 
by himself and others in their construction. It is obvious that one table would suit 
all instruments possessing the same relative proportions. The instrument which 
Mr. Joule presented to the notice of the Association was designed as a type for the 
construction of galvanometers. It consisted of a needle, three inches long, suspended 
in the centre of a coil of six inches diameter. By a simple mechanical contrivance 
the coil could be removed from the instrument, and replaced by others adapted for 
the measurement of currents of different quantities and intensities; but in all cases 
their dimensions were to be exactly similar, and their diameter exactly twice the 
length of the needle, A most important part of the instrument was the needle, which 
was constructed on Dr, Scoresby’s principle, and consisted of two straight and per- 
fectly hard pieces of watch spring, placed at a distance from each other of about ths 
of an inch, the agate cap being fixed between them. The importance of this form of 
needle consisted in the facility it presented of constructing different needles perfectly 
similar to one another with regard to the distribution of magnetism in them, which is 
essential to the accuracy of the same table applied to different instruments, 
Seen! 
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