180 DISSERTATION SECOND. [padt i. 



properties. At the same time, it must be acknowledged, 

 that his credulity on many points, and his fondness for the 

 marvellous, which, with every respect for his talents, it is 

 impossible to deny, take something away from the force of 

 his testimony, except when it is very expressly given. 

 However that may be in the present case, it is probable, 

 that the knowledge of the true properties of these glasses, 

 whether it was theoretical or practical, may have had a 

 share in introducing the use of lenses, and in the invention 

 of spectacles, which took place not long after. 



It would be desirable to ascertain the exact period of an 

 invention of such singular utility as this last ; one that dif- 

 fuses its advantages so widely, and that contributes so much 

 to the solace and comfort of old age, by protecting the most 

 intellectual of the senses against the general progress of 

 decay. In the obscurity of a dark age, careless about re- 

 cording discoveries of which it knew not the principle or 

 the value, a few faint traces and imperfect indications serve 

 only to point out certain limits within which the thing 

 sought for is contained. Seeking for the origin of a dis- 

 covery, is like seeking for the source of a river where 

 innumerable streams have claims to the honour, between 

 which it is impossible to decide, and where the only thing 

 that can be known with certainty is the boundary by which 

 they are all circumscribed. The reader will find the evi- 

 dence concerning the invention of spectacles very fully 

 discussed in Smith's Opticks ; from which the most proba- 

 ble conclusion is, that the date goes back to the year 1313, 

 and cannot with any certainty be traced farther. l 



The lapse of more than two hundred years brings us 

 down to Maurolycus, and to an age when men of science 



? Smith's Opticks, vol. II. Remarks, § 75. 



