MAGNETIC CHARACTERS OF METALS, &c. 629 
ginous metals; but the principal part of his ex- 
periments were limited to copper and _ brass, 
specimens of both of which he found to be mag- 
netic ; and especially after they had suffered the 
operation of hammering. The investigating 
apparatus of this philosopher, like that of many 
subsequent inquirers, consisted of a delicate 
magnetic needle, to the poles of which the speci- 
mens under examination, to prevent commotion in 
the air, were slowly and dexterously presented.* 
* The following are the conclusions at which Cavallo ar- 
rived respecting the magnetism of brass :— 
“‘1st.—Most brass becomes magnetic by hammering, and 
loses its magnetism by annealing or softening in the fire, or at 
least its magnetism is so far weakened by it, as afterwards to 
be only discoverable when set to float in quicksilver. 
“«2nd.—The acquired magnetism is not owing to particles 
of iron or steel imparted to the brass by the tools employed, 
or naturally mixed with the brass. 
‘« 3rd.—Those pieces of brass which have that property, 
retain it without any diminution after a great number of re- 
peated trials, viz., after having been repeatedly hardened and 
softened. 
“4th.—A large piece of brass has generally a magnetic 
power somewhat stronger than a smaller piece, and the flat 
surface of the piece draws the needle more forcibly than the 
edge or corners of it. 
*« 5th.—If only one end of a large piece of brass be ham- 
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