24(f On the Instruments of the Antients. 



ros, where it would be more useful than in any other situa- 

 tion. 



95. " Secondly, The learned of Alexandria might come" 

 to the knowledge of such a mirror, m a way whieh is yet 

 more probable. It is indisputable., that the antients w ere 

 acquainted with burning concaves, and with their property 

 of magnifying objects, which was to them a source of 

 amusement ; as appears from the 1-Uth -chafpftr'-Of Senec&'s 

 book, above quoted. Is it then impossible or even impro- 

 bable, that some Alexandrian philosopher or artist, in amu- 

 sing himself with viewing objects in a well-finished con- 

 cave mirror, six, eight, or more inches in diameter, and* 

 eight or ten feet focal distance, should place his eye in the 

 point from whence distant objects- could be seen to the best 

 advantage ? This appears to me so clear, that I do not think 

 any one will dispute its probability. What very much aug- 

 ments this probability is, that a good effect may be produced' 

 by a mirror of not more than six or seven inches in dia- 

 meter, and five or six feet in: foeal distance. 



96. (( Corollary. From what has been said, then, I 

 conclude, that historians having positively affirmed thai litis' 

 admirable mirror existed, and ivas placed on the Pharos; 

 and the fact, in itself, being neither impossible nor difficult,- 

 but ow the contrary very probable ; ive have no reason ivhat- 

 ever to condemn this piece of history as fabulous; and this is- 

 the point mhich I proposed to prove *." 



97. With this corollary my author closes this his sixth* 

 recreation or memoir, and I shall close the present commu- 

 nication. In my next, I propose to give a brief sketch of 

 his eighth and ninth memoirs, and to conclude with some 

 inferences from the whole of the premises. In the mean 

 time^ dear sir, I remain, very truly, 



Yours, &c. *D. 



* It is observable that Abat takes no notice of the opinion of some of 

 the learned, (whether well founded or not I shall not inquire, ) that trans- 

 parent glass was unknown to the ancient Egyptians. But this circum- 

 stance, even if proved, would not aifect his reasonings respecting the con- 

 cave mirror of the Pharos. — Translator. 



XLI. Sine- 



