630 EXPERIMENTAL INVESTIGATION OF THE 
7. As brass in an alloy so extensively employed 
in the construction of magnetic compass-boxes, 
mered, then that end alone will disturb the magnetic needle, 
and not the rest. 
“* 6th.—The magnetic power which brass acquires by ham- 
mering has a certain limit, beyond which it cannot be increased 
by further hammering. This limit is various in pieces of 
brass of different thicknesses, and likewise of different 
qualities. 
* 7th.—Though there are some pieces of brass which have 
not the power of being rendered magnetic by hammering, yet 
all the pieces of magnetic brass that I have tried lose their 
magnetism, so as no longer to affect the magnetic needle, by 
being made red hot, excepting, indeed, when some pieces of 
iron are concealed in them, which sometimes occurs ; but in 
this case the piece of brass, after having been made red hot 
and cooled, will attract the needle more forcibly with one part 
of its surface than with the rest of it; and hence, by turning 
the piece of brass about, and presenting every part of it suc- 
cessively to the suspended magnetic needle, one may easily 
discover in what part of it the iron is lodged. 
‘* 8th.—In the course of my experiments on the magnetism 
of brass, I have twice observed the following remarkable cir- 
cumstance.—A piece of brass, which had the property of be- 
coming magnetic by hammering and of losing the magnetism 
by softening, having been left in the fire till it was partially 
melted, I found upon trial that it had lost the property of 
becoming magnetic by hammering; but having been after- 
wards fairly fused in a crucible, it thereby acquired the pro- 
perty it had originally, viz., that of becoming magnetic by 
hammering. 
