282 Mr. Lane on the magnetic Attraction 
are evident. Heat, by the converging rays of the sun,* equal 
to that at which glass melts, blackens the oxide, but does not 
render it magnetic, if free from any inflammable matter. It is 
requisite, in this experiment, to protect the oxide, by glass, 
from the dust floating in the air, which otherwise will render 
many of the particles magnetic. I attributed this effect to the 
deoxidising property of light, till by employing a protecting 
glass, the result proved it to proceed from the dust in the 
atmosphere. 
By repeated experiments I found, that heat alone produced 
no magnetic effect on the oxide, and that inflammable matter 
with heat always rendered some of the particles magnetic. 
As the inflammable matter in coal had this effect, I mixed 
some of the oxide with a portion of coal in a glass mortar, and 
continued rubbing them together for some time without any 
magnetic effect. The mixture was then put into a tobacco- 
pipe, and placed in the clear red heat of a common fire ; as 
soon as the pipe had acquired a red heat, it was taken out. 
The mixture was put on a glazed tile to cool, and proved 
highly magnetic. 
I rubbed a portion of the original oxide in a glass mortar 
with a variety of substances, as sulphur, charcoal, camphor, 
ether, alcohol, &c. and found that no effect was produced 
without the assistance of heat. The heat of boiling water, 
moreover, was not sufficient ; but by the heat of melting lead 
I procured magnetism. Small quantities of any inflammable 
matter in a red heat have an evident effect on the oxide. 
Hydrogen, aided by a red heat, renders the oxide magnetic. 
* The lens employed in this experiment was twelve inches in diameter, and the 
heat at its focus was sufficient to melt iron; from Mr. Dollond. 
