Manchester Memoirs, Vol. xliv. (1900), No. VX. 



XII. Grating Films and their Application to Colour 

 Photography. 



By Thomas Thorp. 



Received and read October 17th, iSgg. Received in the present form, 

 May 16th, I goo. 



Some two years ago it occurred to me to try the 

 experiment of taking a cast from a Rowland's metal 

 grating of 14,438 lines to the inch, which I possessed, and 

 after many attempts, I found this to be possible without 

 causing the least injury to the delicate surface of the 

 grating, by using a solution of ordinary commercial 

 celluloid in amyl acetate. Many experiments were, how- 

 ever, necessary before perfect and uniform replicas suitable 

 for optical work were successfully obtained. 



When a grating bright in the first order is used, the 

 replica gives a very faint spectrum in the whole of the 

 orders, but if bright in the second or third order on one 

 side, the first order film spectrum is very bright on one 

 side at least. 



In order to obtain a direct vision spectrum from 

 mounted films, a crown glass prism of about 30'^ is used, 

 the film being mounted on one of the faces, with the lines 

 or grooves of the film parallel to the thin end of the 

 prism. 



When first using such a prism-grating, the film being 

 the replica of a grating bright in the second and third order 

 on one side, it was at once noticed that not only was the 

 spectrum of the first order lengthened, but it was actually 

 brighter than when mounted on a parallel plate of glass, 



Alt gust 1 6th, I goo. 



