I ifi , M A G N 
been expofed to the violet-coloured rays of the fun, have 
Cxa&ly the fame force of polar attraction as nj#ignetifed 
needles. The fcales which are feparated from the furface 
of red-hot iron when hammered, and the particles of burnt 
Heel that are produced from the collifion of a flint and 
lteel, are attracted by the magnet nearly as well as pieces 
of good iron that equal them in bulk. The black calx 
of iron is attracted very weakly. The red calx, or rult, 
•whether it be produced by the action of acids, of Are, or 
by expofure to the atmosphere, is af-traCted very little ; 
but it never becomes quite infenfible of the magnet’s ac¬ 
tion, though it be repeatedly wathed and purified. It is 
obfervable, that a quantity of iron is attracted with the 
leaft force when reduced into the fmalleft bits, or fineft 
powder. The ores of other metals are generally, though 
weakly, attracted by the magnet, thus indicating that 
they contain fome iron : fuels are the ores of lead, of tin, 
and of copper. Native cinnabar is likewife attracted; but 
the factitious cinnabar is not. Of the pure metals, zinc, 
•bifmnth, and particularly cobalt, as well as their ores, 
are alrnott always attracted by the magnet. Antimony, 
unitfs it be firit expofed to a gentle fire, is not attracted. 
Arfenia is not attraCl -d at all. A certain fort of bifmuth 
poflefles a lingular property of being repelled on every 
fide by the magnet. The other minerals, befides the me¬ 
tallic, are almott all attracted by the magnet, at leaft: after 
having been expofed to the aCtion of fire. Of the pure 
earths, the calcareous is leaft, or not at all, and the iili- 
ceous the molt frequently, attracted. 
There are alfo feveral forts of heavy, fliining, opaque, 
black, or dark chocolate-coloured, fand, molt of which, if 
not all, are iron ores, which are fufceptible of magnetii'm. 
Of this kind is the dark-brown fand in emery ; we may 
alfo refer to this clafs molt brafs, and feveral other metals, 
and bricks that have been much burnt in the fire. The 
lnagnetilm of thefe is probably owing to a fmall quantity 
of iron mixed with them. What is in the brafs, Mr. 
Miehell conjectures, may come from the lapis calaminaris, 
which is laid to have often a fmall mixture of iron in it; 
but Mr. Arderon, who fucceeded in giving magnetifm 
and polarity to brafs, has doubts as to the mixture ot iron 
with brafs. As we think this gentleman’s experiments 
and remarks very curious, we lhall give the fubftance of 
.them front the Phil. Tranf. vol. 1 . p. 774.. 
Abjlracl of a Letter from Mr. William Arderon, F.R.S. to 
Mr. Henry Baker , F.R.S. on the giving Magnetifm and Po¬ 
larity to Brafs. Cummun-lcated by Mr. Baker ; and read be¬ 
fore the Royal Socuty, November 16, 1758. 
Dear Sir; For fome time paft I have been making ex¬ 
periments on the magnetifm of brafs; and, amongst many 
pieces that I have tried, find feveral that readily attraCl 
the needle ; but whether they have had this property ori¬ 
ginally, or have received it by hammering, filing, clipping, 
or any other fuch-like caule, I cannot yet determine. I 
have a very handlame coinpais-box made of pure brafs, 
as far as I can judge; the needle being taken out, and 
placed upon a pin fixed properly in a board, and clear of 
all other magnetics, the box will attraCt this needle at 
half an inch diltance; and, if fuffered to touch, will draw 
■it full 90 degrees from the north or fouth points ; and I 
think thole parts of the box marked north and fouth at¬ 
tract the Itrongeft. The cover of the box alfo attracts 
the needle nearly as much as the box itfelf. 
As to your fuppofition, that iron may be mixed with 
the brafs, I do not know ; but I have been informed it 
cannot be, as brafs fluxes with a much lels degree of heat 
than iron, and iron naturally fwims on fluid brafs. Be¬ 
fides, many of the Specimens of brafs I have tried were 
new as they came from the mill, where they were wrought 
into plates, and'I prefume were not mixed ; yet tliele I 
have given the magnetic virtue to, when they had it not; 
.and iome pieces ot brafs, which naturally attraCl the nee- 
.dle, feem to the eye as fine a bright yellow as any other, 
and areots malleable as any I ever met with. 
i 
E T I S M. 
Pieces of brafs without any flOgnetie power, by properly- 
hammering and giving them the double touch, after Mr, 
Michell’s method, I have made attraCl and repel the nee¬ 
dle, as a magnet does, having two regular poles; and I 
now fend you one fuch piece of brafs, which I have thus 
made magnfetical. You will alfo receive a couple of nee¬ 
dles, which I made myfelf after the late Zachary Williams’s 
method, and a little Hand whereon to place them, the 
better to lhow how this magnetic bar attracts and repels 
the needle when property applied ; for it mult be noted, 
that, in making thefe experiments, it is necelfary to em¬ 
ploy a very good needle, about three inches and a half 
long, well and tenderly fet, and not covered with glafs. 
You will obferve, when you try this bar, that the fame 
poles' repel each other, and the contrary poles attraCl; 
which proves this piece of brafs to be endued with true 
magnetic virtue and polarity. However, it muft be noted, 
that, though the fame poles repel each other, yet, like na¬ 
tural magnets, in contaCl, or nearly fo, they attraCl each 
other; therefore, when you would fliow the repellin®- 
power of this brafs bar, you muft not bring it nearer the 
needle than two-tenths of an inch. Magnetic brafs does 
not attraCl iron, not even the leaft particle, fo far as I can 
find ; whether this is owing to the vveakneis of magnetilin 
in the brafs, or to fome other caufe, l don’t pretend to 
know. 
I have tried to infufe magnetic virtue into feveral pieces 
of copper, lead, and pewter; but all my endeavours have 
not been able to make them attraCl the needle at all. In¬ 
deed, when I have held a piece of pewter, that I have 
tried to make magnetical, to the needle, the needle would 
tremble, but not approach the pewter. 
I fend you another piece of brafs, whofe either end at- 
traCls either of the poles; this I have infufed the ma°-ne- 
tic virtue into, and can at any time, fo as to attraCl and 
repel the needle ; but, like fteel that is fet a loiv blue, it 
lofeth that polarity in a few hours; which may arife from 
its being too fliort for its weight, or from its different tem¬ 
per of hardnefs or foftnefs. A third piece I alfo fend you, 
which, with all my endeavours, Ijcannot make attraCl the 
needle in the leaft ; and yet I can perceive no difference 
between the appearance of this piece and that of thofe 
which do. 
Would fome ingenious man purfue thefe experiments, 
perhaps we might have needles made of brafs" to aCl as 
ftrongly as fteel ones do, which would have the advan¬ 
tage of being lefs liable to ruft at lea than fteel ones are. 
But my whole defign was to fliow, that brafs is by no. 
means a proper metal to make compafs-boxes of, or to be 
employed in any inftrument where magnetifm is con¬ 
cerned. For as it is demonitrable, beyond all contradic¬ 
tion, that lome brafs is found endued with a power of at¬ 
tracting the magnetic needle; that other pieces are capa¬ 
ble of receiving it either by accident or defign (let it be 
from its being mixed with iron, or any other caule what¬ 
ever), brafs muft be a very improper metal for compafs- 
boxes, as it may occallon many fad and fatal accidents. 
Norwich, Nov. 20, 1758. W. A. 
It is well known, that brafs has been.fometimes found 
to affeCl and difturb the magnetic needle ; bur, to give 
magnetifm and polarity to brafs, has nor, that I have yet 
heard, been before attempted. I therefore have taken the 
liberty to lay tiie above account before this Royal Society ; 
and have alfo brought the pieces of brafs mentioned 
therein, which have been thus made magnetical. 
London, Nov. 15, 1758. H. Baker. 
Mr. Cavalio more recently made feveral experiments, 
with a view of afcertaiuing the magnetifm of brafs, and in- 
veftigating the caufe of it. The relult is as follows : It 
appears, he lays, “ 1 ft. That molt brafs becomes magnetic 
by hammering, and lofes the magnetifm by annealing or 
foftening in the fire, or at lealt its magnetifm is ft?far 
weakened by it, as afterwards to be only difeoverabie when, 
fet afloat on quickiilver. 2dly. That the acquired ma°--. 
netifin is not owing to particles of iron or fteel imparted 
to 
