New Engine for Riding. 55 



It will be perceived from the foregoing that the provision respect- 

 ing insulation, isolation, general stability and comparative freedom 

 frcjni temperature variations, combined with easy accessibility, 

 leaves little of importance unprovided for. Naturally, the result 

 of favourable conditions in the housing and surroundings of the 

 machine was a pronounced improvement in the quality of the grat- 

 ingti ruled, even apart from further mechanical improvements 

 resulting from a more extended acquaintance with the working of 

 the machine. 



This general account of the more important mechanical features 

 of the Ruling Engine will, it is hoped, convey a fair idea of its 

 structural divergences from other machines designed for ruling 

 gratings; that is, so far as descriptions of such machines have 

 been published. Two such descriptions, more or less complete, have 

 recently appeared, viz., that of the Blytheswood machine, now at 

 the National Physical Laboratory, and a partial account of a new 

 machine designed by Professor Michelson, of the Chicago Univer- 

 sity. Descriptions of Ruling Engines of earlier design, as for 

 example those of Nobert, Rutherford, and Rowland, have been 

 published. With perhaps the exception of the Blytheswood Engine, 

 few of the descriptions convey to the reader any very detailed or 

 important information concerning the actual construction of a 

 machine of this character. Therefore, as much of the work entailed 

 differs from ordinary instrument work and involves an intimate 

 appreciation of minute values, it may be useful to give some 

 account of the actual work involved in constructing special parts of 

 the machine. The methods adopted were largely due to unavoidable 

 limitatiiins, and better results might liave been attained by other 

 means. 



This record is primarily the fulfilment of a definite obligation to 

 the University whose generosity has made the building of a machine 

 possible of accomplishment. That the information concerning its 

 construction, which is here given, may be of service to others who 

 may be engaged on similar or related work, affords the possibility 

 of additional usefulness. 



In conformity with the foregoing, the following special parts of 

 the machine appear to merit more detailed attention, namely : — 



1. The Screw. 



2. The Ratchet Wheel. 

 .3. The Thrust Plate. 



4. The Bulinq Diamond. 



