' [ 62 Z ] 
happy in his invention, he fell upon one, which lef- 
fen’d his former good opinion of the parabolical Spe- 
culum, and made him more fenfible of the incon- 
veniencies attending it, or thofe of any other form, 
that had any great degree of concavity • and, in a 
word, engag’d him intirely in favour of his new 
thought, which was put in execution in the following 
manner : 
He eredted a frame, on which he placed five plane 
fpeeula, of equal given dimenfions, with fuch incli- 
nations as made them all throw their refieded rays 
upon the fame place, at more than one hundred feet 
difiance. When he had fet the firfi fpeculum, he 
went and laid his hand upon the place, whereupon 
he caus’d the rays to fall, and found it warm ; when 
he added thofe of the fecond, the heat was doubled j 
the third increas’d the heat in the fame proportion ; 
and the fourth being added, the heat was fcarce to 
be borne ; but the fifth made it intolerable. From 
whence he concludes, that, by multiplying thofe fpe- 
cula, the heat might be fo increas’d, as to fet fire to 
combuftible matter at greater diftances, according to 
the number apply ’d. 
Now becaufe I think it a matter of fome ccnfe- 
quence, in the learned world, to afcertain to every 
author the praifes due to his labours and difcoveries, 
and to fhew this author’s application of the invention 
to the confirmation of this Archimedean fad; I think 
it alfo incumbent on me to give the Society his own 
words upon it, which he himfelf has reduced to a 
problem. 
PrOB LEM A. 
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