532 Mr. T. Gaffield on the Action of Sunlight on Glass. 



clows. The oldest specimen was one of crown glass, set in a 

 church in Lexington, Massachusetts, in 1794, from which the 

 windows were removed in 1846, and since used as covers for 

 hotbeds. The original colour, found by removing the putty 

 from the edges, was a light green ; and the present, after seventy- 

 three years' exposure, is a purple colour. I have never yet met 

 any one who has seen glass in original imported packages of the 

 purple colour made by exposure to sunlight ; and until I do, I 

 shall adhere to my opinion, that all purple or rose-coloured glass 

 which is seen in our city windows was made so by said exposure. 

 I have very fortunately found an octogenarian who has furnished 

 me with some glass which was imported, he thinks, from some 

 part of Germany, which is of a light-green or yellowish-green 

 colour. The glass was imported more than thirty years ago. 

 Much of that which has been set in his windows facing the south 

 is now purple. An experiment with the original glass, com- 

 menced this summer, showed a perceptible change in colour in 

 one day ; and in two weeks the change towards purple was so 

 marked that I have no doubt that this colour will be distinctly 

 visible in less than a year. If two years were occupied in the 

 erection of the Beacon Street houses, or any others in which the 

 plate glass purpled by sunlight is found (as I am informed was 

 the fact in some cases), then the result of the single experiment 

 named above is a sufficient reason for the mistaken belief of many 

 occupants and owners today, that the glass was purple when 

 imported. It was probably changed from yellowish green to 

 purple before the houses were finished and the owners had taken 

 possession. 



The action of sunlight which I have spoken of in this article 

 must not be confounded with that called "rust" or " stain," 

 which is occasioned by exposure to the weather, and manifests 

 itself in two ways : — first, by a disintegration and roughening of 

 the surface, sometimes producing all the effects of ground glass; 

 and secondly, by an apparent formation of an infinitesimal coat- 

 in g of oxide on the surface, on which the play of light gives all 

 the colours of the rainbow, as with the action of light on the 

 infinitesimal grooves of the surface of mother-of-pearl. This 

 is simply surface-action, whereas the action of sunlight per- 

 meates the whole body of the glass wherever the rays directly 

 strike it. 



The writer of this article (compiled in the midst of the busy 

 duties of mercantile and official life) makes no pretension to ac- 

 curate scientific knowledge, but gives the results of his obser- 

 vations and methodical experiments on a well-known pheno- 

 menon, in the hope that they may add some mite to the sum 

 of human knowledge, and may stimulate and aid those who 



