J 4 On tlie Catoptrical and Dioptrical 



Pursuing the same course along the coast they entered a 

 very narrow channel, on coming out from which they found 

 another port, which they called Gorostiza. They were now 

 near the mouth of the great channel towards the north. 

 Proceeding tlien south-east they arrived at Cape Scott, 

 which is without the channel, and which is the most westr 

 ern point of the great island Quadra y, Vancouver. Some 

 leagues to the east of this cape, and in the open sea, there 

 are two very large islands called those of Lanz. But when 

 they arrive;.! at that space of sea which separates them from 

 Cape Scott, they were obliged to return to search for an- 

 chorage, which is at the mouth of the strait. Next day 

 thcv steered for Nootka, where they arrived on the 30th 

 ofAu2;ust, after era ploy i-ig four months in saihng round 

 the large islaiul. 



[To be continued.] 



LETTER IV. 



IT. On the Catoptrical and Dioptrical Imtrumcnts of 

 the Antients : ivith Hints respecting their Revival, or 

 Reinvention, and Improvejnent in modern Times. 



[Continued from our last volume, p. 3+9.] 



9. J- Hus, with \hc hdp oi Abat , I have in some degree 

 followed, without intending it, a plan I have somewhere 

 seen recommended, namely, to prosecute historical inqui- 

 ries backwards ; that is, to begin with our own times, or 

 lather with times not much anterior to our own, and pro- 

 ceed, by retrograde steps, to more antient periods, till at 

 last we approach the wilds of imcertalnty and fable. — I shall 

 now add a few miscellaneous remarks and quotations ; some 

 of which did not before occur to me, and others could not 

 well be introduced in my former communications. 



10. And first, I thuik it right to lay before the reader the 

 followins; passage from Bitffon, which I have just found, 

 and which, it must be owned, is not very consonant with 

 the account of the destruction of the mirror of Ptolemy 

 Euergetes, given by ylbat, from Crusius. (See Lett. iii. 

 § 32.) I have not the means of reconciling tiiem ; and, if 

 I had, I am rot sure that I should make the attempt. For 

 the question is not. How, or when, or by whom, this op- 

 tical instrument was destroyed ? but Whether it really pro- 

 duced the effects recorded of it ? And that it did^ Abat, al- 

 lowing 



