MAGNETISM. 
118 
fllver, copper, lead, tin, fmall cylinders of glafs, a piece 
of chalk, a fragment of bone, and different kinds of wood. 
This gentleman proved, that the force of torfion of the filk 
thread is fo flight, that, in order to draw' it round the en¬ 
tire circle, it would require a force fcarcely equal to the 
one hundred thoufandth part of a gramm, (or about one 
feven hundredth part of a grain.) A quantity fo minute 
cannot therefore fenfibly derange the meafure of magnetic 
force in the different bodies ; and its effeft, even if it 
were admitted to be of perceptible magnitude, may alfo 
be urged in proof of the general conclufion of citizen Cou¬ 
lomb, becaufe the magnetic power muff overcome this re¬ 
finance of the thread in order to manifeft itfelf. Our au¬ 
thor gives, in the third volume of the Memoirs of Natural 
Philofophy and Mathematics of the National Inftitute, a 
very Ample formula to determine the magnetic force of a 
body from the time of its ofcillations; and he thinks he has 
proved, that all the elements which enter into the compofi- 
tion of our globe are fubjecfed to the magnetic power; and 
that the whole mafs collectively forms one Angle magnet. 
The opinion of the general influence of magnetifm on 
all terreftrial bodies Was previoufly maintained by our 
countryman Dr. Gilbert, though Coulomb has certainly 
the merit of having put it to the teft of experiment. Dr. 
Gilbert had propofed an experiment on the fubjeft which 
completely failed. He faid, that if a fpherical form were 
given to a magnet, and if its two poles were at the extre¬ 
mities of a diameter 5 this fpherical magnet, when placed 
in complete equilibrium, and fulpended on its poles, 
would turn round its axis in twenty-four hours; for as 
the earth, adds he, is but a large magnet, it muff'have a 
fimilar motion. This would have been a pretty It rang 
roof of the motion of the earth, at lea It around its axis ; 
ut M. Petit, an induftrious philofopher of the 17th cen¬ 
tury, having taken the trouble to make the experiment 
propofed by Gilbert, the fmall magnetic globe remained 
perfectly motionlefs. This does not however prevent the 
motion of the'.earth from being certain, and it may even 
be confidered as a large magnet ; though father Gran- 
damy concluded, from the failure of Gilbert's experi¬ 
ment, that the earth was motionlefs. Thus much for 
bypothefes and conjectures. Let us return to fomething 
more certain. 
It is very common to make ufe of a fmall magnet, held 
in the hand, for the purpofe of feparating iron-filings, 
turnings, &c. from thole of brafs or finer metals. In lieu 
of this tedious method, Mr. Rofs, of Prince’s-ftreet, Soho, 
London, invented a machine for effecting this reparation 
in the large way ; for which he received a reward from 
the Society of Arts in the year 1810. By this invention, 
many magnets may be employed at once, combined and 
attached to a machine on a large fcale. The magnetic 
hammers are fo contrived as to take up the iron-filings 
from the mixture of them with other filings, or metallic 
particles, placed in trays or end-boxes, and drop them 
into the receiving-box in the centre, which is effected by 
the alternate motion of a winch-handle, working the two 
magnetic hammers placed at two angles of a quadrant or 
anchor. In proportion to the power of the magnets and 
to the force of the blow given by the hammers, a great 
quantity of iron is feparated from the brafs, by the alter¬ 
nate motion, and dropped into the receiver placed in the 
centre of the machine. This machine, of which a model 
is preferved in the Society’s repofitory, is reprefented on 
Plate II. at fig. n. A is an axis of brafs, and B a handle 
‘Upon the end of it : C is a piece of biafs in foim of an 
anchor, at each end of which a horfe-flioe magnet is fixed, 
in the manner fliown at fig. 12.. vvhere c is the arch of. the 
anchor, and cl a piece of brafs having a hole through it to 
receive the legs ee of the magnet, which is fixed to the 
arch by a fcrew^/j tapped into the arch. The anchoi is 
mounted upon the pivots of the axis A, in a frame E, 
jig. 11, which indoles it; on the outfide of the frame two 
blocks of woou EF are fituated, in each of which a hoi-, 
low or tray is formed to receive the filings which are to 
be feparated from the iron they contain in thefe hollow*. 
The magnets fixed at the ends of the anchor Itrike upon 
the filings, and feleft, by the magnetic attraction, all the 
iron among them ; the anchor is then turned over by the 
handle B, and the oppofite magnet ftrikes in the other 
hollow F. At this time the other magnet is juft over the 
axis ; and, by the jerk of its oppofite ftriking the block F, 
the iron-filings are fhaken off, and fall down in the bottom 
of the frame, or receiver; in this manner the handle B, 
being moved backwards and forwards, ftrikes the magnets 
alternately in the two blocks F ; and, at the fame time that 
one ftrikes, the oppofite one is cleared from the iron it 
has picked up by the fliock. G is a fcreen of thin board 
to prevent the filings being fcattered. 
By means of the magnet, Mr. Lampadius (Neues Journal, 
fur Chemie und Phyiik, 1814) contrived an eafy and con¬ 
venient inftrument to determine the weight of fmall quan¬ 
tities of matter, and toafcertain the fmallefl change in the 
weight of bodies under examination. It ferves like wife the 
purpofe of a magnetometer , and may be employed for other 
hygrofcopical and fimilar purpofes. This inftrument is re¬ 
prefented at fig. 13. and the following is the in venter's de- 
i'cription of it: “I lufpend by an oiled - ii 1 k thread ainode- 
rately-even glafs rod 24 inches long. The point of fufpen- 
fion is eight inches from the left end of the rod, fo that the 
other arm of the lever is (ixteen inches in length ; and at 
the extremity of it is fixed a filver pointer, to (how the 
motion of the arm. To the fhorter end of the lever is 
fixed a fmall leaden weight, fecured from oxydation by- 
being varnifhed ; and from the extremity of the longer 
arm of the lever a fmall glafs fcale is fufpended by filken 
threads. The weight is fo regulated that the pointer 
ftands at o. By putting one grain of apothecaries’ weight 
into the glafs fcale, the pointer finks a little ; and itill 
farther on adding two, three, four, &c. grains. The po- 
fitions of the pointer with each weight in the fcale are 
marked on a circle againft which the pointer plays. As 
the diltance between each of thefe pofitions is inch, I 
divide it into 100 parts, and thus I obtain a means of de¬ 
termining the change of weight amounting to ^io part of 
a grain. To prevent the lever from being agitated back¬ 
wards and forwards, it is made to play between two per¬ 
pendicular glafs rods placed at a. Suppofe," now, that I 
have melted or heated a fmall piece of matter by means 
of a fire urged by oxygen gas, and that I. with toafcer¬ 
tain what change has taken place in its weight; my in¬ 
ftrument puts it in my power to do fo. In order to de¬ 
termine the magnetic energy of a body, I take a piece of 
it weighing one grain, =100 of my divisions, and put it 
into the final 1 glafs fcale. Then, by means of a ferew, I 
apply a magnet capable of fupporting one pound of iron, 
always in a direction exactly under the lcale in which 
the fubftance to be examined is depofited. When the 
magnet comes within the fphere of attraftion of the body, 
the pointer ufually ltarts a little up, as, for example, to 
95. I now caution-fly pu(h the magnet forward with the 
ferew. At lalt the fcale del'cends towards the magnet. 
I then obferve the pointer again. Suppofing it to ttand 
at 155, I confider 55 as indicating the magnetic energy 
of the body ; fo that in the prefent cafe this energy is a 
little more than equal to halt the weight of the body. I 
repeat the experiment fix or ten times, and never find 
more than yoo P art °f difference.” This magnetometer 
gave the magnetic energy of iron =55, that of nickel 
=235, and that of cobalt =225. 
Of ARTIFICIAL MAGNETS. 
Magnetifm, or the property of attrafting iron, and of 
turning towards a certain point ot the heavens, is not fo- 
peculiar to the magnet as to be incapable of being com¬ 
municated ; but no bodies have yet been found lulcepti- 
ble of this communication, except iron and fttel. About 
a century ago it was believed that contact alone, or the 
continued prefence of a magnet, could produce this ef¬ 
feft 5 but a method has fines been dilcovered, to render a 
