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f. Experiments upon Metals^ made with the Burning- 
Clafs of the Duke of Orleans/ By Monfteur 
Geoffrey, F, ^ S, 
''HE Duke of Orleans^ out of the defire he has to 
promote ufeful z\rts and Sciences, having permit- 
ted fuch of the Royal Academy of Sciences as have had 
moft Experience in fubjeds of this Nature, to make ufe of 
his Burning- glafs ^ I took this Opportunity to examine 
the diSerent Changes that Metals fufPer when placed in 
the Focus of this Glais, whofe Heat and Efficacy far 
(urpafEs the force of our common Fires. 
The Burning glafs is three Foot in Diameter 5 it col- 
leds the Rays of the Sun at ten Foot diftance, where 
it forms a Focus of about three Inches over, which is 
again contraded by means of an other Glafs- Lens to, 
an Inch Diameter, and confequently is render’d three 
times as ftrong. 
I fiiall only relate here what I have obferv’d upon 
the four Imperfed Metals, viz. Iron, Copper, Tin, and 
Lead : And Qiall fay nothing at prefent of Gold or Silver 
becaufe as their Analyfis feems to me much more difficult 
than that of the other Metals 5 I (hall forbear Inquiries 
upon themj fill I have examined as far as poffible into 
the Nature and Compofition of the former. 
What was a great hindrance to me in making thefe 
Experiments in the Focus of the Glafs, was the diffi- 
culty I had to find any Matter capable of holding the 
Metals in fufion. 
Char- 
