150 ON THE TELESCOPE. 



Obfervations I am confcious, Sir, that what I now fend you, is put to- 



relating to the .t ... T _ T 



invention of the& in a ver y halty manner. Were my time at my own 



telefcope. difpofal, I would endeavour to make it more fit to meet the 



public eye; but I am induced to fend you thefe hints in their 

 prefent ftate, becaufe I rely as much upon the candour as on 

 the learning and abilities of Sir H. Englefield. If I am mif- 

 taken, he will fet me right; and if I have any foundation for 

 my opinion, he can eafily illuftrate my hypothefis by the paf- 

 fages which agree with it, in the old writers on optics and 

 aftronomy. I am, Sir, 



Your obliged humble fervant, 



E. Q. 

 Oxford, Feb. 10, 1805. 



P. S. Since I finiQied the letter, which I fent to you on the 

 10th inn 1 . I have met with a paffage, which appears to me to 

 decide the quetlion or^ which I wrote to you. It is in Kepler's 

 book, which he publifhed at Francfort in ]60i-, under the title 

 , of dfironomia pars optica. The beginning of it is entitled 

 Faralipomena in Vitellionem, He difcuffes the nature of the 

 eye, and at p. 178. he begins a fet of proportions on the man- 

 ner in which it ads as the organ of vifion. The 2Sth of thefe 

 propositions is that which makes mod immediately for my pre- 

 fent purpofe; it is at p. 200, and he enumerates it in the fol- 

 lowing words. 



** Qui remota diflinfte' virlenf, propinqua confnfe; iis per- 

 " fpicilla convexa profunt. Qui vero confufe vident remota, 

 " juvantur concavis perfpicillis." 



The mere quotation of thefe words is fufficient for the proof 

 of what I have afft-rted ; but as it may afford fome amufement 

 to your readers, I will add his remarks upon them as (hortly 

 as poflible. — " Quanta adrairalio" he fays, " rei tantae tarn 

 late propogatum ufum: & (amen caufum ignorari haclenus." 

 J. B. Porta, he adds, profefles to give tne reafon in his op- 

 tics: but this book he was never able to m^et with. Kepler 

 then very ably refutes the opinion of thofe, wno fuppofe this 

 effect to be produced by the increafing or dimimfhing of the 

 apparent magnitude of the object. He offers with confider- 

 able diffidence his own method of accounting for the pheno- 

 menon. He fuppofes that in the cafes mentioned in the pro- 

 portion the vifion is imperfect, in as much as without the in- 

 tervention 



