I2« 
MAGNETISM. 
In this manner, when the piece of fteel has been rubbed a 
fufficient number of times on one fide, turn the other fide 
upwards, and repeat the operation till it has acquired a 
fufficient degree of magnetifm. In this operation, the 
fame precautions muff be followed as were recommended 
for the method of communicating the magnetifm to ftraight 
bars, viz. the magnets DF, EG, as well as the magnets 
H, I, mult be placed fo that their fouth poles may be to¬ 
wards that extremity of the bent fteel which is required 
to be made the north pole, and their north poles towards 
the other extremity. The magnets, I, H, mult be firft 
placed on the middle of the bent fteel ; and after having 
drawn them over one leg of it as often as over the other, 
in order to let the magnetic centre fall juft in the middle 
of the bent fteel, they are removed, &c. 
Whenever a fteel bar, or in general a piece of ferrugi- 
Bous fubltance, is rendered magnetic by applying two bars, 
or whenever two magnetic poles are applied ta it at the 
fame time, as ufed in this and the preceding experiment, 
the operation is ufually called the double touch, in diftinc- 
tion from the Jingle touch, which is when only one mag¬ 
netic pole is applied to it. 
If a perfon have only one magnetic bar, with which he 
wilhes to give magnetifm to a needle or other bar, the 
only way of effecting it is, to apply one pole of the mag¬ 
netic bar, A B, fig. 26, to one extremity, C, of the nee¬ 
dle, and to draw it all along the furface of it till it reaches 
the other extremity D; then the magnet, being removed, 
mult be applied again to the extremity C, and mud be 
drawn over the needle as before. Thus the needle mult 
be rubbed feveral times, by which means it will acquire a 
confiderable degree of magnetifm. It tnuft be obfervetf, 
that the extremity of the needle which the pole of the 
magnet touched laft acquires the contrary polarity. 
Thus, in the prefent inftance, if B be the north pole of 
the magnet, the extremity, D, of the needle will after¬ 
wards be found to have- acquired the fouth polarity, and 
the other extremity, C, the north. In this operation 
therefore, it is evident, that, after the firft ftroke,.when 
the magnet is applied again to C, this extremity, having 
acquired the north polarity, will have that power deltroyed 
by the vicinity of the north pole, B, of the magnet; fo 
that it feems that every ftroke undoes what was done in 
the preceding. However, the fact is, that by repeating 
the ftrokes the power is increafed ; but, in general, this 
method will never be fo advantageous as when more than 
one magnetic pole is ufed ; hence it ought not to be ufed, 
excepting in cafe of neceffity, viz. when one has only one 
magnetic bar. 
The following experiments, for difeovering what kind 
of fteel is moft fit to receive the magnetic power, are from 
the Memoirs of the Academy of Sciences of Paris. Th« 
author of the paper is M. Briffon. “ Philofophers have 
taken great pains, and made many experiments, to find 
out the belt manner of touching bars of fteel, fo as to con¬ 
vert them into artificial magnets; but I know not that 
any one has fought to difeover, by comparative experi¬ 
ments with different kinds of fteel, what kind is moft pro¬ 
per for this purpofe, that is, what kind is capable of receiv¬ 
ing the greateft quantity of magnetic power. I have em¬ 
ployed myfelfin making fome experiments upon this fub- 
jett, and (hall now give an account of them to the academy. 
“ I caufed five pairs of bars, of different kinds of fteel, 
to be made by a very good workman, who knows perfectly 
well how to work in fteel, and how to temper it. They 
are all exaftly equal to each other in length, in width, in 
thicknefs, and even, except a few grains, in weight; they 
are alfo, as near as could be, equally well wrought and 
poliftied, and all tempered as hard as pofiible. Each of 
thefe bars is fix inches and three quarters of a line in 
length, fix lines wide, and two lines thick. I placed them 
in pairs, according to Dr. Knight’s method, keeping them 
feparate by a flip of wood, and making them corffmunicate 
at each of their extremities, by the contaft of a piece of 
&ft iron, nine lines in width. That I might know them 
from each other, I marked each of them with a different 
figure. The bars marked 1 were of Englilh call fteel; 
thofe marked 2 were caft fteel of Amboife ; thofe marked 
3 were common fteel of Amboife; thofe marked 4 were- 
of German fteel, known by the name of etojfe de pons ; and 
the bars marked 5 were of Englilh fteel. 
“ I have two pairs of bars, feventeen inches and fix 
lines long, one inch wide, and fix lines thick ; their mag¬ 
netic power is very (trong, and I quicken that power by 
touching them alternately one with the other. With one 
of thefe pairs of bars I touched all the five pairs above- 
mentioned ; in doing that, I conftantly ufed the fame pair, 
which I took care to have always in the fame good ftate ; 
that is to fay r , I retouched them every time with the other 
great pair, that I might, as far as was pofii'ole, have all 
circurnftances alike, and not have reafon to fulpecl any 
difference between the five kinds of fteel, except their 
different difpofition or capability to receive the magnetic 
power. I touched all thefe bars according to the manner 
of M. Antheaume; I placed them all, pair by pair, con¬ 
nected by the piece of loft iron before-mentioned, and fe- 
parated by a flip of wood, in the direction of the mag¬ 
netic meridian ; and, in order to touch them, I placed my 
two great bars end to end, with their contrary poles to¬ 
wards each other, and leparated only by a card thrice 
doubled. I then let them Hide gently five times back¬ 
wards and forwards, from one end to the other of each of 
the bars, upon each of their broad Airfares, but without 
going beyond their extremities, and always beginning and 
leaving off in the middle of the bar. Thefe bars having 
been touched in the above-mentioned manner, I endea¬ 
voured to find out their power of attraction. For that 
purpofe I fattened each pair together by means of two 
bands of copper; each band having a ferew to tighten ir, 
one of which ferews had a ring to it, by which the bars 
might be hung up. At the upper end, the bars were con¬ 
nected by the piece of iron already mentioned ; at the 
lower end, inftiad of fuch a piece, I placed a ring of foft 
iron, rounded in fuch a manner as to touch the bars only 
by a narrow line. To this ring was adapted a hook, in¬ 
tended to receive the handle of a little tin bucket in which 
the weights were put. Every thing having been thus dif- 
pofed, I fuccelfively, and gradually, loaded each pair of 
bars with grains of lead, till the iron ring leparated from 
the bars. I took care, however, not to load them in this 
manner, till the ring had adhered to the bars for the fpace 
of twenty-four hours. 
“ Tiie following is the refult of thefe experiments -. 
The bars marked 1, of Englilh caft lied, which weMi, 
together, 5 ounces, 4 drachms, and 51 grains, fuftained, 
including the weight of the ring, 2 pounds, 13 ounces, 
and 5 drachms; which is fomewhat more than 8 times 
their own weight. The bars marked 2, of caft fteel of 
Amboife, which weigh, together, 5 ounces, 4 drachms, 
57a grains, fuftained, including the weight ot the ring, 
1 pound, 12 ounces, 2 drachms, and 36 grains ; which is 
rather more than 5 times their own weight. The bars 
marked 3, of common ft ;el of Amboife, which wei°-h, to¬ 
gether, 5 ounces, 4 drachms, 46^ grains, fuftained, in¬ 
cluding the weight of the ring, 5 ounces, 7 drachms, and 
57 grains; which is, as is obvious, only a little more than 
their own weight. The bars marked 4, of German fteel, 
known by the name of etojfe de pons, which weigh, toge¬ 
ther, 5 ounces, 4 drachms, and 53 grains, fuftained, in¬ 
cluding the weight oftthe ring, 4 pounds, 3 ounces, 3 
drachms, and 3 grains; which is rather more than 12 
times their own weight. The bars marked 5, of Englilh 
fteel, which weigh, together, 5 ounces, 4 drachms, & and 
40 grains, fuftained, including the weight of the ring, 4 
pounds, 15 ounces, 1 drachm, and 36 grains; which is 
more than 14 times their own weight. 
“ From the foregoing experiments it appears : Firftly, 
That Englifh fteel is the molt fit for receiving the magne¬ 
tic power, and that it ought to be preferred to every other 
kind. Secondly, That the German iteel, known by the 
name 
