New Engine for Riding. 87 



threaded bar on which additional weights are screwed for regu- 

 lating to a nicety the pressure upon the dianiond ruling point. The 

 ruling system is thus completely controlled and balanced upon the 

 two hardened centres of the suspension frame. 



Considering the long period during which interest has been more 

 or less centred upon fine ruling and the means for accomplishing 

 it, either for use as spectroscopic gratings, test rulings or micro- 

 meters — all of which recjuire very fine accurately spaced lines — but 

 little has been written concerning the diamond Avith which such 

 ruling is effected. As already mentioned, Nobert guarded with 

 jealous care his knowledge of the subject, the result of years of 

 patient work, and whicli he regarded as an important secret known 

 only to himself. Tpun Xobert's death his ruling machine passed 

 eventually into the possession of the late Dr. von Heurick, of Antwerp, 

 who was interested in ruling in its relation to the microscope. Some 

 years ago the writer had correspondence with Dr. van Heurick, who 

 stated that he had spent some time in trying to rule test plates 

 similar to those prepared by Nobert, but without success. In the 

 course of his experiments he had had prepared by one of the 

 most skilled diamond workers in Antwerp a set of diamonds exactly 

 similar to those found with the Nobert machine and Avith Avhich 

 Nobert presumably ruled his plates. Dr. van Heurick generously 

 presented to the writer three of the prepared stones. Whilst it was 

 a matter of great interest and pleasure to obtain these diamonds, 

 the knife edges of which appeared to have been exquisitely worked, 

 the results obtained by their use were most disappointing. Indeed 

 the lines obtained with these carefully prepared knife-edged gems 

 Avere quite unsuited for any but the coarsest ruling. Prior to this 

 experience with the diamonds from Dr. van Heurick, an interest- 

 ing paper by Profesor Rogers, of Baltimore, U.S.A., had ap- 

 peared. This paper contained much information concerning the 

 operation of a ruling diamond Avith prepared knife edges and Avitli 

 edges resulting from fracture; the latter AA-ere stated to be more 

 or less unsatisfactory. His method of using .either knife edges or 

 fractured splinters appears to have been diametrically opposed to 

 that of otlier AA-orkers; certainly to that of the Avriter. 



Professor Rogers, for example, emphasises the statement that a 

 ruling diamond should produce, or did in his experience produce, 

 a distinct and characteristic sound during the act of ruling. So 

 familiar had this note become to his sense of hearing that he Avas 

 accustomed to judge of tlie behaviour of a particular diamond by 



