Obituary. 21 



the 10-band plate was pronounced by Mr. Nelson to be the finest 

 photo -micrograph of ruled bands he had ever seen. (J.E.M.S., 

 1898, p. 690 ; 1899, p. 122.) Mr. A. A. C. E. Merlin, in his note 

 " On the Measurement of Grayson's New 10-Band Plate," says, 

 " it is doubtful if any production of the kind has hitherto approached 

 so nearly to perfection." (J.RM.S., 1911, p. 160.) 



Other communications regarding these plates in the Journal 

 tire : in 1904, p. 393, " On Grayson's 120,000-Band Plate," by 

 E. M. Nelson ; in 1910, p. 5, " On the Measurement of Grayson's 

 10-Band Plate," by A. A. C. E. Merlin ; p. 144, •* On Measurement 

 of the First Nine Groups of Grayson's Finest 12-Baud Plate," by the 

 same writer; p. 701, Note "Grayson's Photo-micrographs of his 

 Eulings," by E. M. Nelson ; in 1911, p. 449, " A Report on the 

 Grayson's Euling presented by Mr. C. Beck to the Pioyal Micro- 

 scropical Society," by E. J. Spitta. Other references to the plates 

 and photographs appear in the Journal for 1899, p. 355 ; 1902, 

 p. 385 ; 1910, p. 801 ; 1911, p. 421. 



In the volume for 1910, p. 239, is an article by Grayson, 

 reprinted from a local publication, and entitled, " On the Produc- 

 tion of Micrometric and Diffraction Piulings." The writer says: 

 " Some years ago I had occasion to use some finely-ruled glass 

 plates, not exceeding 0*01 in. thickness, the lines upon them 

 ranging from 0*02 in. to 0-004 in. apart. These I found were 

 not readily obtainable commercially, so that I had to devise some 

 method of producing them for myself. After a few experiments 

 T soon found I had no difficulty in ruling lines greatly exceeding 

 in fineness and accuracy any of the kind I had hitherto seen, and, 

 as the matter was interesting to me from a microscopical stand- 

 point, I pursued it apart from my immediate requirements." A 

 brief account is given of the apparatus employed, which was 

 largely composed of glass, and which was afterwards much modified, 

 to make it capable of the greatest amount of precision. Lines 

 ruled with it of 120,000 to the inch are the finest so far resolved. 

 The ordinary glass covers were found to be too hard, but Grayson 

 after several trials succeeded in annealing them, making them 

 both softer and tougher. The method of selecting and preparing 

 the diamonds is described, also that of mounting the covers. 

 Grayson says that he tried every, or almost every, known cement 

 and wax-cell, but in every instance the cover-glass sooner or later 

 became coated with minute crystals or beads of moisture. Eealgar 

 was then tried, and for a long time without success, but finally the 

 usual method of using it (dissolved in bromine) was abandoned, 

 and after many trials it is claimed that success was obtained by 

 the use of thin films produced by sublimation. A number of test 

 diatoms mounted in this way were exhibited at the Society's 

 meeting in October 1898. 



Accounts of Grayson's work having come under the notice of 



