136 Description of a Burning Mirror. 
sun in its diurnal arc is not so rapid, but that one person 
may direct ten mirrors close to each other ; a circumstance 
which considerably diminishes the ere and labour at~- 
tending the operation. 
We “conclude that M. Peyrard has brought the con- 
struction of burning glasses composed of several plain mir- 
rors to a perfection “which these machines had not hitherto 
acquired, and which seems.to us to be worthy of the at- 
tention of the Class. 
Signed Cuartes, Rocuon, Monce, 
Paris, 3d August, 1807. Reporter. 
The Class approves of the above report, and adopts its 
conclusions. 
4th August, 1807. Signed DELAMBRE, ' 
Perpetual Secretary. 
M. Peyrard’s Description of his Machine. 
This burning mirror consists of an assemblage of plain 
silvered looking-glasses. Every glass is arranged in ine 
following manner : 
An object glass AB (fig. 1, Plate IV.) is moveable on its 
axis between two collars CC, C’C’, which are fixed with a 
piece of metai DD. 
_ The small aperture of the glass is at A, and the large one 
at B: two wires cross each other at right angles at the 
centre of the large aperture. 
A screw E.acts on the object glass, and isin it in the 
position which we wish to give to it. 
The object glass is mounted ona stand like a common 
object glass, so that we may direct its axis towards. a given 
point: two screws F and G retain it in its position. ' 
The middle of the object glass is surmounted by a cy- 
linder M’ M’, the upper base of which 1s parallel to the axis 
of the object. glass. 
A branch of iron HHH, wrought square, is fixed with 
the object glass. 
A framed looking-glass turns on two pivots MM, OO. 
The straight lme which passes through the centre of the 
Pivots is tangent to the posterior face ‘of the nuirror, and 
perpendicular on the axis of the object glass. 
The black trace NN, which is oneasioned by the scratch 
in the plating, is divided into two equal parts by the axis of 
the mirror. 
* The large aperture of the object'g glass is surmounted with 
a plate of metal which is fixed with it. Before this plate is 
a square plate ZZ, on which are traced the straight lines 
XX, YY, which intersect at right angles. The square * 
plate 
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