[ 494 ] 
in fome meafure re-eftablifhed. This Machine, for 
fo I muft call it, confifts of 140 fmall plain Mirrors, 
each of about 4 by 3 Inches fquare 5 they are fixed 
at about a Quarter of an Inch Diftance from each 
other, upon a large wooden Frame about 6 Feet 
fquare, ftrengthened with many crofs Bars of Wood 
for the mounting of thefe Mirrors. Each of them 
have three moveable Screws, which the Operator 
commands from behind, fo* contrived, that the Mir- 
ror can be inclined to any Angle in any Diredion 
that meets the Sun 5 and by this means the folar 
Image of each Mirror is made to coincide with all 
the reft. 
There are in all, as I told you, 140 Mirrors; but 
they tried the Experiment this Morning with 24 
only 5 for fo many, and no more, were then ready 
for the Purpofe : The Effed was, that, in very few 
Seconds of Time, a combuftible Matter they had pre- 
pared with Pitch and Tow, daubed upon a Deal- 
Board, was fet on Fire, and burn'd vigoroufly at the 
Diftance of threefcore and fix French Feet, Judge 
now of the Effed 140 will produce 5 and whether 
the Invention may not be improved to the Height of 
all that has been advanced of Archimedes by the 
Ancients. The only Difficulty they found was, to 
make the folar Images of the Mirrors coincide 5 but 
this is owing to the yet Imperfedion of their Me- 
thod of mounting, which may be eafily improved.. 
The Dimenfions I have given in of the Mirrors 
and Frame were only guefied at from View, for I 
have not meafur'd them ; fo you muft not exped 
they will fquare or tally mathematically in the ut- 
moft Rigour. Nor indeed did I think it neceffary 
to 
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