OF THEEE LARGE LOADSTONES. 
389 
full energy of N : if we now put another strip of soft iron 
round C D of the magnet, we in the same way cut off from 
action another portion of the magnetic surface of N : and 
if we proceed to add more strips of iron, as EF, GH, IK, 
and LM, we gradually weaken the effective power of N, 
till we nearly prevent it altogether. This might be illus- 
trated by numerous experiments. Let us select one. Let 
us apply to the poJes of a horse-shoe magnet (as shewn in 
PI. XII. fig. 3.) two such pieces of soft iron as are usually 
employed to connect the two kinds of magnetism (T and 
U), and leaving them in contact with iron-filings, and they 
will be attracted to T and U in great abundance : now 
place a similar piece of soft iron (see fig. 4.) on both poles, 
and V will not attract iron-filings, for the magnetic circle 
is complete. If, again, we place the pieces of soft iron, 
T and U, .as shewn in fig. 5, then T will shew scarcely 
any power of attraction ; but if we draw away U, the at- 
traction of T becomes powerful, and is again lost when we 
return U to its situation. From all these facts, then, it 
w^ould appear, that, when we complete the magnetic circle, 
we prevent considerably the escape of the attracting power, 
or rather, I should say, we retain the acquired activity of 
the magnet. And it was most likely for this purpose that 
these magnets were covered with an iron armature. 
The largest of the loadstones, independent of its arma,, 
ture and connecting iron, weighs 125i pounds; and it 
measures, 
In length, - - - ^ - lOf inches, 
— breadth, 8| 
height, ----- 9i 
When I received it, it could carry 163 pounds ; but, by 
gradually increasing the weight, I afterwards brought it to 
support 165 pounds, exclusive of a connecting iron of 
