called the inclination or dipping of the mag- 
net. 
5. Any magnets may, by proper methods, 
be made to impart those properties to iron or 
steel. 
A plane perpendicular to the horizon, and 
passing through the poles of a magnet when 
standing in their natural direction, is called 
the magnetic meridian ; and the angle which 
the magnetic meridian makes with the me- 
ridian of the plane where the magnet stands, 
is called the declination of the magnet at that 
place. 
Of magnetic attraction and repulsion . — 
"When a piece of iron is brought within a cer- 
tain distance of one _aLthe_poles of a magnet, 
it is attracted by it ; and if the iron is at li- 
berty to move, it adheres to the magnet, and 
cannot be separated without some force. It 
appears at first sight, that the attraction lies 
only in the magnet, but experiment proves 
this attraction to be mutual ; the iron attract- 
ing the magnet as much as the magnet at- 
tracts the iron. Place the magnet and the 
iron upon two separate pieces of cork, or 
wood, floating upon water, at a little distance 
from each other, and it will be found that the 
iron moves towards the magnet, as well as the 
magnet towards the iron ; but if the iron is 
kept steady, the magnet will move towards it. 
This attraction is strongest at the poles of 
a magnet, and diminishes in proportion to 
the distance of any part from the poles, so 
that in the middle between the poles there 
is no attraction. This may be easily per- 
ceived by presenting a piece of iron to vari- 
ous parts of- the surface of a magnet. 
The intensity of the attractive power di- 
minishes also, according to the distance from 
the magnet. If the magnet and iron touch 
each other, it requires a certain degree of 
force to separate them ; if the iron is re- 
moved a little way from the magnet, an at- 
traction will be plainly perceived, but not so 
powerful ; and by increasing this distance 
the attraction will be much diminished. 
* The law of diminution of this attraction 
is not yet known. Some have imagined that 
it diminishes in proportion to the square of 
the distance, others as the cube of the dis- 
tance. ' But either from the difficulty of the 
subject, or on account of the experiments 
having been made without sufficient accu- 
racy, the question remains yet undecided; 
it is only known that the attractive force 
decreases faster than the simple ratio of the 
distances. , ' 
As magnetic attraction takes place only 
between poles of different names of different 
magnets ; that is, the north pole of one mag- 
pet attracts the south pole of another; conse- 
xjuently magnetic repulsion acts only between 
poles of the same name of different magnets. 
Thus, if the north pole of one .magnet is op- 
posed to the north pole of another magnet, 
or if the south pole be opposed to the south 
pole- of the other, then those magnets will 
repel each other, and that nearly with as 
much force as the poles of different names 
would attract each other.. 
But infrequently happens, that though mag- 
nets are placed with the same poles towards 
each-other, yet they either attract each other, 
or shew a perfect indifference. This, at first, 
keems to contradict, the above-mentioned 
general law; but this difficulty is removed 
t»v the following considerations ; 
magnetism. 
When a piece of iron is brought within a 
certain distance of a magnet, it becomes, in 
fact, itself a magnet, having the polarity, the 
attractive and repulsive properties for other 
iron, &c . ; that part of it which is nearest to 
the south pole of the magnet, becoming a 
north pole, and the opposite part a south 
pole, or vice versa, according to the' end of 
the magnet presented. Thus it A B, Plate 
Magnetism, fig. 1, be an oblong piece of 
iron, and be brought near the north pole 
N of the magnet N S, then this piece of iron 
while standing within the magnet’s sphere of 
action, will have all the properties of a real 
magnet, and its end A will be found to be a 
south pole, while the end B is a north pole. 
Soft iron, when placed within the influence 
of a magnet, easily acquires these properties; 
but they last only while the iron remains in 
that situation, and when it is removed its 
magnetism vanishes immediately. But with 
iron containing carbon, and particularly with 
steel, the case is very different ; and the harder 
the iron or the steei is, the more permanent is 
the magnetism which it acquires from the 
influence of a' magnet; but it will be in the 
same proportion more difficult to render it 
magnetic. 
If a piece of soft iron, and a piece of hard 
steel, both of the same shape and size, are 
brought within the influence of a magnet at 
the same distance, it will be found that the 
iron is attracted mor'e forcibly, and appears 
more powerfully magnetic, than the steel ; 
but if the magnet is removed, the sott iron 
will instantly lose its acquired properties, 
whereas the hard steel will preserve them fora 
long time, having becomean artificial magnet.* 
Neither the magnetic attraction nor re- 
pulsion is in the least diminished, or at all 
affected, by the interposition ot any sort of 
bodies, except iron, or such bodies as contain 
iron. 
The properties of the magnet are not affect- 
ed either by the ’presence or by the absence 
of air. Heat weakens the power of «. mag- 
net, and subsequent cooling restores it, but 
not quite to its former degree. A white 
heat destroys it entirely, or very nearly so; 
and hence it appears, that the powers of 
magnets must be varying continually. Ca- 
vallo observes, that iron in a full red heat, 
or white heat, is not attracted by the mag- 
net ; but the attraction commences as soon 
as tiie redness begins to appear. 
The attractive power of a magnet may be 
considerably improved by suspending a 
weight of iron to it by its power ot attraction, 
which may be gradually increased ; and also 
by keeping it in a proper situation, v.iz. with 
its north pole towards the north,, and its 
south pole, consequently, towards the south. 
On the contrary, this power is diminished by 
an improper situation, and by keeping too 
small a piece of iron, or no iron at all, ap- 
pended to it. 
In these northern parts of the world, the 
north pole of a magnet has more power than 
its south pole; whereas, the contrary effect 
has been said to take place in the southern 
parts. 
Amongst the natural magnets, the smallest 
generally possess a greater attractive power 
in proportion to their size than those of a 
larger size. 
It frequently happens, that a natural mag- 
net, cut off from a larger loadstone, will be 
able to lift ft greater weight of iron than the 
original loadstone itself. 
As both magnetic poles together attract a 
much greater weight than a single pole ; and 
as the two poles of a magnet generally are 
in opposite parts of its sunace, in which ease 
it is almost impossible to adapt the same 
piece of iron to them both at the same time ; 
therefore it has been commonly practised to 
adapt two broad pieces of soft iron to the 
poles of the stone, and to let them project 
on one side of the stone; for those pieces 
become themselves magnetic while thus situ- 
ated, and to them the piece of iron or weight 
may be easily adapted. Those two pieces 
of iron are generally fastened upon the stone 
by means of a brass or silver box. The 
magnet in this case is said to be armed, and 
the two pieces of iron are called the armature. 
Fig. 2. represents an armed magnet, 
where A B is the loadstone ; C I), C D, are 
the armature, or the two pieces of soft iron, 
to the projections of which D D the iron 
weight F is to be applied. The dots E C D 
C U represent the brass box, with a ring at 
E, by which the armed magnet may be sus- 
pended. 
Artificial magnets, when straight, are 
sometimes armed in the same manner ; but 
they are frequently made in the shape of a 
horse-shoe, having their poles at the trun- 
cated extremities, as at N and S, fig. .3, in 
which shape it is evident that they want no 
armature. 
Most probably the magnet attracts iron 
only ; but when it is considered how uni- 
versally iron is dispersed throughout nature, 
it is evident that a vast number of bodies- 
must on that account be attracted by the 
magnet more or less forcibly, iii proportion 
to the quantity and quality of the iron they 
contain. Indeed, it is wonderful to observe 
what a small portion of iron will render a body 
subject to the influence of the magnet. 
The polarity of the magnet . — Every mag- 
net has a south and a north pole, which are 
at opposite ends ; and a line drawn from ene 
end to the other, passes through the centre' of 
the magnet. Here it must not be understood; 
that the polarity of' a magnet resides only 
in two points of its surface ; for in reality, 
it is the 'one half of the magnet that is pos- 
sessed of one kind of polarity, and the other 
half of the other kind of polarity ; the poles, 
then, are those point's in which that' power 
is the strongest. 
T he line drawn from one pole to the other, 
is called the axis of the magnet ; and a line 
formed all round the surface of the magnet, 
by .a plane which divides the 'ftxis into two 
equal parts, and is perpendicular to it, is 
called the equator of the magnet. 
It is the polarity of the magnet that renders 
it so useful to navigators. When a magnet 
is kept suspended freely, so that it may turn 
north and south, the pilot, by looking at the 
position of it, can steer his course in any re- 
quired direction. Thus, if a vessel is steered 
towards a certain place which lies exactly 
westward of that .from which it set out, the 
navigator must direct it so, that its course 
may be always at right angles with the di- 
rection of the magnetic needle of his com- 
pass, keeping the north end of the “hlagnet 
on the right-hand side, and of course, the 
south end on the left-hand side of the ves- 
sel ; for as the needle points north and south. 
