V. REFLECTION^ ETC. 229 



914. Jamin's Optical Bank of Diffraction. 



//. Lloyd, Trinity College, Dublin. 



914a. Jamin's Apparatus with Parallel Mirrors. 



M. Lutz, Paris. 



914b. Large Steel Mirror. M. Lutz, Paris. 



914c. Series of Barton's Iris Buttons, consisting of 

 gold and steel faces engraved upon which are numbers of very fine 

 lines, illustrating most beautifully iridescence or decomposition of 

 light from ruled surfaces. The lines on the large steel button 

 are 100, 200, 400, 500, 1,000, 2,000, and 4,000 to the inch. 



Robert C. Murray. 



915, Optical Bank, improved by Professor Clifton, to 

 observe the interference and diffraction of light and measure the 

 bands. Elliott Brothers. 



915b. Collection of Six Gratings (reseaux} by Nobert of 

 Barth, and Steeg of Homburg. Teylcr Foundation. Haarlem. 



Nobert B. of 1,801 lines in six Fans lines. 

 C. of 3,001 

 D. of 10,801 in one Paris inch. 

 E. of 2,001 



F. of 3,001 

 Steeg A. of 3,201 lines in five millimetres. 



Robert B and C were used by Prof. Van der Willigen for the determination 

 of the wave-lengths of fifty lines in the solar spectrum. 



91 5c. Specimens of Circular Gratings (Reseaux) photo- 

 graphed on Glass. The rays of the successive circles limiting 

 the opaque and transparent parts are in the proportion of 1 to 

 4/2, */3, 4/4, 4/57 &c. 



91 5d. Large Circular Grating on smoked Glass, trans- 

 parent traces of equal width, having rays in the proportion of 

 V 3, 4/7, 4/lT, </15, 4/T9, &c. J- Louis Soret, Geneva. 



See " Memoire sur les Phenomenes de Diffraction produits par les Reseaux 

 circulaires" (Archives des Sciences physiques et naturelles, 1875, Vol. 52, 

 p. 320. Poggendorffs Annalen, 1875, No. 9). 



915e. Telescope with Circular Gratings. Constructed 

 by the Geneva Association for the Construction of Scientific In- 

 struments. J* Louis Soret, Geneva. 



1st arrangement. The smoked glass grating is used for objective with a 

 common eyepiece. Looking at a gas jet (for instance) at seven metres 

 distance, the distance of the objective and the eyepiece being from 34 to 41 

 centimetres, then pulling out one of the tubes the image of the jet is seen 

 reversed, and coloured more or less. By pushing in the tube as much as 

 possible, the second image is seen green-coloured. 



