232 On the Catoptrical and Dioptrical 



wish to be understood whenever I have made use of that 

 word in the course of this letter. The Abbe Haiiy found it 

 necessarv to take a similar precaution at the beginning of 

 the excellent work (Traite de Physique) he has lately pub- 

 lished. He says : " This word Nature, so frequently in 

 our mouths, can only be looked upon as an abridged ex-> 

 pression, either for the result of those laws which the Great 

 Creator has imprinted on the universe, or for that aggregate 

 of beings the works of his hands. Nature, thus viewed in 

 its true light, is no longer a subject of cold and sterile spe- 

 culation. The study of its productions, of its phaenomena, 

 ceases to be a mere exercise of the mind; it moves the heart, 

 and strengthens the moral virtues in man, by awakening in 

 his mind sentiments of respect and admiration at the sight 

 of so many wonders bearing the visible characters of infinite 

 power and wisdom." 



With these sentiments 1 remain, sir, yours, 



July 13,1804. A. Q. BCJEE, 



XL. On the Catoptrical and Dioptrical Instruments of the 

 Antients. 



LETTER III. 



[Coniinutd from p. 190.] 



€e Part Second. Conjectures on the Existence and the 

 Reality of the Mirror of Ptolemy*. 



49- <e It is by.no means so easy for us to satisfy ourselves 

 with respect to the reality of the fact which we are exa-: 

 mining, as to demonstrate its possibility. The proofs of 

 the possibility of facts subsist throughout all ages ; time 

 cannot destroy them ; and they may always be discovered 

 by diligent search. But when the question concerns things 

 which have existed formerly, but do not now exist, we have 

 only remaining monuments, or the testimonies of historians, 

 to convince us of their past existence. If such monuments 

 and testimonies have not come down to us, we have no 

 other means whatever of establishing such facts. 



50. u Hence, in our researches concerning the possibility 

 of facts, we may find complete evidence. But, in inquiring 

 into their real existence, we are frequently obliged to stop 



* The reader is nquesred to correct th« numbers of the paragraphs in 

 the first part, wliich ar- 4.8 La all. 



in 



