periodical colours produced by grooved surfaces, 47 



of grooved surfaces upon light. As the subject was to a cer- 

 tain extent new, many of the results which I obtained seemed 

 to possess considerable interest, and I accordingl}r communi- 

 cated to the Royal Society of Edinburgh a general account of 

 them, which was read on the Sd of February 1 823. The in- 

 terruptions, however, of professional pursuits prevented me, 

 but at distant intervals, from pursuing the inquiry ; and hav- 

 ing found that M. Fraunhofer was actively engaged in the 

 very same research, with all the advantages of the finest appa- 

 ratus and materials, I abandoned the subject, though with 

 some reluctance, to his superior powers and means of investi- 

 gation. During a visit paid to Edinburgh by the Chevaher 

 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 atten- 

 tion 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 consi- 

 deration 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 w, represents the breadth 

 of each groove, or of the surface that is removed, while the other 

 71, represents the breadth of the intermediate space, or of the 

 original surface that is left. If the image of a candle is seen 

 by reflexion from such a surface, the trace of the plane of re- 

 flexion being parallel to the grooves, we observe the colourless 

 image of a candle in the middle of a row of prismatic images 

 arranged in a line perpendicular to the grooves. The colour- 

 less image of the candle is formed by the original portions 7i 

 of the metallic surface, w hile the prismatic images are formed 

 by the sides of the grooves m. This may be demonstrated 

 ocularly by increasing m, and consequently diminishing Ji till 

 the latter nearly disappears. In this case, the intensity of the 

 prismatic images rises to a maximum, while the ordinary co- 



* 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. 



