2i On Catoptrkal and Dioptrical Instniments. 



use of them to Julius Ccesnr, while he says nothhig as to 

 the time and circumstances of their invention P 



Query 5th. Whether the antient maxim of concealing 

 from the people at large truths of which, it was supposed, 

 they could make no good use ; a maxim which, as we have 

 seen, was applied to this very subject even by so modern 

 an author as Dr. Recnrde, did not peculiarly expose such 

 truths, thus floating, so to speak, on the breath of a few 

 adepts, to the danger of being lost in the revolutions which 

 too frequently disturb or subvert society ; especially before 

 copies of what )7}ight have lean ihovght Jit to be committed 

 to writing* could be n}ultiplicd by the press? (See Lett. ii. 



§16.19.) 



Quert/ Gth. Whether, notwithstanding these disadvan- 

 tages, considerable remnants of optical knowledge have 

 not escaped the reserve of philosophers and the fvirv oif re- 

 volutionists ; and whether, if At'cit and others have proved, 

 or rather, if experiments prove, that simple Iciiscs and con- 

 cave mirrors have the same effects as telescopes ; and if 

 yibut ha?, moreover, made it probable that Ptnlemij Ener- 

 gcies applied a concave mirror to the same use; it would be 

 absurd to conclude, that instruments equivalent to telescopes 

 are, in fact, extremelv antient? (See Lett. iii. § 12. 23, 

 &c.) 



Query Jfh. Whether this conclusion be not additionally 

 justified by the proofs, which the same author has adduced, 

 of the dexterity of the antient manufacturers of glass ; proofs 

 which reach from verv distant times down to the days of 

 Vilvllio, Pcccam, and Roger Bacon P (See the former part 

 of this letter.) 



Quen/ 8th. Whether, after the evidence stated {and mnc/i 

 more might no doubt be discovered) it would be rash, or ab- 

 surdy or incensisteut tvith. the undoubted, pretensions of mo- 

 dern inventors, to suppose that the knowledge of some such 

 instrument as the telescope, has been concealed among the 

 learned from very remote ages ; and that, strictly speaking, 

 such knowlrdge has only been published, and with other parts 

 of optics, greatly augmented and improved, in moctern times P 



* Dr. H'/t.'o>!, in his article Ga/i/t'o, after enumerating the writings of 

 tint great man. adds: " Besides all these, he wrote many other pieces, 

 which were unfortunately lost thiough his wife's devotion,' {say t//^otry), 

 •« who, solicited by her confessor, gave him leave to peruse her hus- 

 band's manuscript. ; of which he tore and took away as maitj as he said 

 •wdc not fil 10 be- piiliusbcd." 



' 2 Thc?e 



