On a new Species of coloured Fringes. 353 



while smoothness, compactness, and solidity were given to her 

 walls, by filling the intervals of all the timbers with short wood — 

 an expedient attended with manv advantages, which 1 shall not 

 dwell on, as he could not comprehend them. He goes on to say 

 that the " decks are not loose as in the old system." Now, really, 

 when a Doctor, who is besides F.R.S. L. & E., has sailed to 

 the Baltic in a shii), tor the purpose of giving colour to a quarto 

 volume which might as well have been written in Grub-street, 

 we cannot help eitlier suspecting his capacity for observation, 

 or doubting his assertion resjiecting the voyage, as the Leith 

 traders (of u'hich I have built two or three) are not in the 

 slovenly practice of carrying their decks about them " loose." 



But I have duelt longer on his review than it merits, and shall 

 conclude by advising him to pursue a Pythagorean system — ■ 

 Seven years of silence and seclusion to his chamber, with a diet 

 of oatmeal, may perhaps increase his knowledge, and neutralize 

 his superacetic disposition. 



I am, &c. 

 Glasgow, Sept. 14, 1815. A. StEWART. 



LXV. On a new Species of coloured Fringes produced ly the 

 Reflcclimi of Light between two Plates of parallel Glass of 

 equal Thickness. By David Brewster, LL.D. F.fl.S. 

 Edin. & F.A.S. E.* 



i-zURiXG a series of experiments in which I was lately engaged, 

 for the purpose of determining the law of the polarization of 

 light, l)y successive reflections from plates of parallel glass, I 

 observed that all the images of the luminous body which were 

 formed by more than one reflection, were crossed by parallel 

 fringes of coloured light, when the two plates had a small in- 

 clination to each other; and that these fringes suffered consi- 

 derable changes, by varying the j)ositicn of the plate v/Ith regard 

 to the incident ray. 



These coloured fringes seemed at first to have the same origin 

 as those of thick plates, which were discovered by Newton, and 

 afterwards examined bv the Duke de Chaulnes, Mr. Brougham, 

 and Mr. .1 ordan ; and I considered the second plate of glass as 

 performing the part of the (juicksilver in Newton's glass mirror, 

 or of the metallic speculum in the ex])eriments of the Duke de 

 Chaiilnes and Mr. 'Brougham. A more attentive examination, 

 however, convinced me that this was a mistake, and that the 

 coloured fringes constituted a new class of phaenomena, liavii:ig 



* From tljc Traiihaclions of the Royiil Society of Edinburgh for 1815. 



Vol. 4(i. No. 21 1. Nov. 1815. Z a different 



