Q£ ON PHILOSOPHICAL DISCOVERIES. 



Letter from a Correfpondent, relating to the apparent Reflection 

 of Cold and the Invention of the Telefcope, as noticed by Sir 

 11. C. Englkfield in laji Month's Journal. 



To Mr.. NICHOLSON. 

 SIR, 



IN juftice to ProfelTor Pictet, I traft you will have the good- 

 nels to infert in your next number the words of a note in his 

 Ejfai de Phyfique, p. 31, where he defcribes his experiment on 

 the apparent reflection of cold : 

 Apparent reflec- " Les Academiciens del Cimento avoient effuye de concentrer 

 tion of cold. \ e f ro id au foyer d'wi miroir concave ; mats Us avouent eux- 

 memes, que leur experience avoit ete faite d'uu maniere trap in- 

 exacle pour qu'on put en rien conclure de certain." 



Perhaps Profellbr Piclet (peaks too lightly of the experiment 

 of the Academicians; but fo far was that experiment from 

 being forgotten, that the account of it has been very lately 

 reprinted in the firft volume of the Journals of the Royal 

 Inftitution, p. 224; a work to which your correfpondent, 

 who has revived the fubject (page 1 of your lafl Number), 

 has himfelf contributed fome valuable papers. 

 Kepler did not With refpect to the invention of the telefcope, give me 

 invent or J™ ^ leave to obferve, that perfpicillum means (imply the fight of an 

 teifore Galileo, agronomical inlirument, having a fmall perforation. If the 

 comet in queffion was furrounded by a fmall round and well- 

 defined nebulofity, fuch a fight might eafily produce the effect 

 attributed to it. A telefcopic fight is ufually called perfpi- 

 cillum vitreum. Galileo fays, in a work publifhed in 1610, 

 that he was informed of the invention of telefcopes about nine 

 months before. Kepler wrote, in 1611, a valuable work on 

 the theory of dioptrics, in which the conftruclion of the agro- 

 nomical telefcope is defcribed. Had he been the original in- 

 ventor of the Galilean telefcope, he would not omitted this 

 opportunity of fubftantiating his claim to fo important a dii- 

 covcry. 



I am, Sir, 



Your very obedient fervant, 



ALETES. 



Facls 



