20 
SUPPLEMENT. 
be smaller, and in the opposite hemisphere, the corresponding 
figures would be larger in proportion. 
It was once the general opinion, that the poles of every 
magnet must be diametrically opposite to one another, as the 
poles of natural magnets are generally found to be so, but 
Doctor Gowen Knight has demonstrated, by experiments, that 
the poles of magnets may be disposed in every possible direction. 
The most extensive case, that can come under our consideration, 
is, when the magnetic poles are situated neither in the same nor 
opposite meridians, and this seems to have been the real posi¬ 
tion of these poles, ever since any observations of the declination 
of the magnetic needle have been made. In this case then, the 
lines of no declination cannot be either in the direction of the 
meridian or along the equator, as in the former cases, but a kind 
of curves, which are variously inclined to both, and they divide 
the surface of this globe into two parts, but those parts are not 
hemispheres, as in the last case, for they may be of very differ¬ 
ent extent. 
If the magnetic poles be situated in meridians nearly opposite, 
the curvatures of those lines are the less, but as the magnetic 
poles approach nearer to the same meridian, the curvatures of 
the lines of no declination become greater, until they almost 
touch one another, something in form like the figure 8, and at 
last they complete the two great circles. 
The lines of the second order, which correspond to the greatest 
equatorial declination, if the magnetic poles be situate in meri¬ 
dians nearly opposite, have a declination nearly equal to the 
angle formed between the magnetic and true poles. But as the 
magnetic poles approach near the same meridian, this declination 
decreases, till at last it entirely vanishes together with the lines 
of the first order, and leaving only the lines of the third order. 
The foregoing cases will be found to convey every thing that 
is necessary towards an explanation of the declination of the 
magnetic needle. It is, however, a most important circumstance 
for our consideration, that in the Berlin Memoirs for the year 1757. 
Euler has, from a series of mathematical calculations, actually 
laid down the spot where the position of the magnetic pole is to 
