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XXV. On a new series of periodical colours produced by the grooved surfaces of 

 metallic and transparent bodies. By David Brewster, L.L.D. F.R.S. L. 8^ E. 



Read May 21, 1829. 



IN the year 1822, when I received from Mr. Barton some very fine specimens 

 of his Iris ornaments, I availed myself of the opportunity of performing a series 

 of experiments on the action of grooved surfaces upon light. As the subject was 

 to a certain extent new, many of the results which I obtained seemed to possess 

 considerable interest, and I accordingly communicated to the Royal Society 

 of Edinburgh a general account of them, which was read on the 3rd of Fe- 

 bruaiy 1823. The interruptions, however, of professional pursuits prevented 

 me, but at distant intervals, from pursuing the inquiry ; and having found that 

 M. Fraunhofer was actively engaged in the very same research, with all the 

 advantages of the finest apparatus and materials, I abandoned the subject, 

 though with some reluctance, to his superior powers and means of investiga- 

 tion. During a visit paid to Edinburgh by the Chevalier Yelin, a friend of 

 Fraunhofer's and a distinguished member of the Academy of Sciences of 

 Munich, I showed him the general results which I had obtained ; and as he 

 assured me that the phenomena which had principally occupied my attention 

 had entirely escaped the notice of his friend*, I was thus induced to resume 

 my labours, the results of which, in relation to one branch of the subject, I 

 shall now submit to the consideration of the Society. 



When a flat and polished metallic surface is covered with equal and equi- 

 distant grooves, we may characterize it by the relation of two quantities, one 

 of which m represents the breadth of each groove, or of the surface that is re- 

 moved, while the other n represents the breadth of the intermediate space, or 



* The memoir of M. Fraunhofer was read to the Bavarian Academy of Sciences on the 14th of 

 June 1823 ; and has no relation to the subject of this paper. 



