8 o Mr. CavALLo’s Magnetlcal Experiments , &c. 
I have likewife often obferved, that a long continuance in a 
fire fo ftrong as to be little ftiort of melting hot, generally dimi- 
nifhes, and fometimes quite deftroys, the property of becoming 
magnetic in brafs. At the fame time, the texture of the metal 
is confiderably altered, becoming what fome workmen call 
rotten . From this it appears, that the property of becoming 
magnetic in brafs by hammering, is rather owing to fome 
particular configuration of its parts, than to the admixture of 
any iron ; which is confirmed ftill farther by obferving, that 
Dutch plate-brafs (which is made not by melting the copper, 
but by keeping it in a ftrong degree of heat whilft furrounded 
by lapis calaminaris) alfo poffefles that property ; at leaft all 
the pieces of it, which I have tried, have that property. 
I am, &c. 
T. CAVALLOe 
