ON THE HISTORY OF OPTICS. 4:7'^ 



itself. Both of these doctrines were combated by Aristotle, who thought it ab- 

 surd to suppose that a visual influence §hould be emitted by the eye, and that 

 it should not enable us to see in the dark; and who considered it as more pro- 

 bable that light consisted in an impulse, propagated through a continuous 

 medium, than in an emanation of distinct particles. Light, he says, is the 

 action of a transparent substance; and if there were absolutely no medium 

 between the eye and any visible object, it would be absolutely impossible 

 that wc should see it. 



It is said that Archimedes made a compound burning mirror, of sufficient 

 power to set on fire the Roman ships: in this form the story is scarcely pro- 

 bable, although the possibility of burning an object at a great distance by a 

 collection of plane mirrors has been sufficiently shown by the experiments 

 of Buffon. It is, however, not unlikely that Archimedes was acquainted 

 with the properties of reflecting surfaces, and that he confirmed his theories 

 by some experimental investigations. The work on catoptrics, attributed 

 to Euclid, contains the determination of the eflfects of reflecting surfaces of 

 different forms; but it is not supposed to be genuine. The existence and 

 the magnitude of the atmospheric refraction were well known to Ptolemy, 

 and a treatise of this astronomer on the subject is still extant in manu- 

 script. 



The mathematical theory of optics, or the science of dioptrics and cat- 

 optrics, made some advances in the middle ages from the labours of Alhazen 

 and Vitellio. Alhazen was mistaken in some of his propositions respecting 

 refraction ; Vitellio, a native of Poland, gave a more correct theory of this 

 subject, and constructed a table of refractive densities, showing the supposed 

 proportions of the angles of incidence and refraction in the respective 

 mediums. 



The invention of the magic lantern is attributed to Roger Bacon, and 

 the lens was soon afterwards commonly applied to the assistance of defective 

 sight. It has been much disputed whether or no Bacon was acquainted with 

 telescopes; the prevalent opinion is, that the passages, which have been alleged 

 to prove it, are insufficient for the purpose; but there is reason to suspect, 

 from the testimony of Recorde, who wrote in 1551, not only that Bacon had 



VOL. I. 3 p 



