[Proc. Eot. Soc. Victoria, 30 (N.S.), Pt. I., 1917]. 



Ar'I". VI. — Description of a New Dividing Evijine for Ruling 

 D iffract ion Grat ings. 



By H. J. GRAYSON, 



University of Melbourne. 



(With Plates YI.-XVII.) 

 [Read 12th July, 1917]. 



Intpoductopy. 



The fcjllowing pages comprise a description of a New Dividing 

 li^ngine designed and 'constructed by the writer for the ruling of 

 Diffraction Gratings and also, vrith certain modifications, of accu- 

 rate scales. Prior to 1910, when this work was begun, a consider- 

 able experience of the difficulties inherent to worlv of a related 

 ■character had already been obtained; particularly with respect to 

 the ruling of very fine or closely spaced lines, known as " Test 

 Rulings, "1 used for testing the resolving and defining power of 

 MicroscojDe objectives. Rulings for this purpose, known as Nobert's 

 Test Plates, were first made by Herr Nobert Avith the aid of a 

 machine the design of which remained a carefully guarded secret 

 until his death. On this machine he ruled his celebrated Diffraction 

 Gratings, which Avere the first of their kind available for spectro- 

 scopic work. 



Several papers, 2 descriptive and critical, referring to the author's 

 earlier work, will serve to show that this fresh undertaking — the 

 construction of a machine for ruling Diffraction Gratings — though 

 far more difficult than anything of the kind previously undertaken 

 by him, had at least a reasonable prospect of being successful, 

 provided health permitted and suitable mechanical facilities were 

 available. 



For a time progress Avas somewhat sIoav, OAving to lack of essential 

 appliances and the very limited time available for so great an 

 undertaking. Both these draAvbacks Avere, hoAvever, largely over- 

 come — mainly by an extension of the time available for construc- 



1 "The Microscope," Naegeli and Schwendener, 18S9. Translation. 



2 " A Wave-length Comparator for Standards of Length," hy A. E. H. Tiitton, AI.A., D.Sc, 

 F.R.S. Phil. Trans. Royal Soc. of London (Series A), vol. 210, pp. 1-34. " On the Aleasurement of 

 Grayson's Ten-band Plate," by A. A. Eliot Merlin, Journ. R. Micro. Soc, 1010, pp. 5-8. "On the 

 Measurement of Grayson's New Ten-Band Plate," by A. A. Eliot Merlin, Journ. R. Micro. Soc, 

 1911, pp. 160-163. "Comparative Micionietic Measurements, by Dr. Marshall D. Ewell, Journ. R. 

 Micro. Soc, 1910, pp. 537-554. Also many "Notes" and "References" to Grayson's Rulings by 

 E. M. Nelson, Esq., Journ. R. Micro. Soc, earlier vols. 



