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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- 
bruary 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, x 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. 
