_ Description of a Burning Mirror. 14} 
Knowing the value of AP, I take its square root ; from 
this root I cut off GD, i. e. 53",72, and I find 229™,25. 
Whence I conclude that the image reflected is double the 
surface of the glass when it is removed 22,25. 
In order to find the distance DQ, we should make this 
\ 3 
proportion : 1: 3:: (53",72)*: GQ. In order to find the 
other distances, we ought to conduct ourselves yn a similar 
manner. 
[have calculated these distances, and I find the following 
results ; 
- The Image being The distance is 
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DPE 2 .a9 deggie ha: Mee os Ola 
Quadruple .....e.eeeeee ees 53 372 
Quintuple .....eeeee+s eee > GG 541 
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Beptuple. >... beep shes sale? 2 OP peae 
Octuple ....eeeceecseees++ 98 522 
Wontple’s)..3..sere esc LON ste 
Decaphe is. esters re cole ot’ RLOE SEO 
It is almost unnecessary to say, that these distances 
would be double, triple, quadruple, &c. if the diameters of 
my glasses, instead of being five decimetres, were ten, 
fifteen, twenty, &c. decimetres. 
Let us suppose a certain number of my mirrors, and sup- 
pose that at a very small distance the images of these mirrors 
nnited on the same object are capable of producing a_cer- 
tain degree of heat. It follows, according to the results 
which [ have obtained, that in order to produce the same 
degree of heat at a distance of 22”,25,39",33, 53,72, &eay 
we must double, triple, quadruple, &c. the number-of 
mirrors. It also follows, that at one of the distances cal- 
culated above, we may produce a heat at least equal to that 
which would be produced by the heat of the sun, repeated 
as often as we pleased. 
But how many times must we repeat the heat of the 
sun in order to boil water, set fire to wood, or melt, calcine 
and evaporate metals, &c.? These questions are not yet 
resolycd. By means of my mirror they might. And iv 
order to gratify im some measure the curiosity of my 
readers, I shall try to resolve some of these questions, taking 
as a basis the experiments which Buffon made with his 
burning mirror. 
_ The glasses of which Buffon’s mirror was composed 
were each six inches bigh by eight broad. In order to 
simplify 
