New Engine for Ruling. 53 



motion of the main driving rod (52) to the ruling carriage. When, 

 however, the clamping blocks are brought closer to 47 and secured, 

 the free motion of 44 is restricted to a precise interval, which may 

 vary from 0.01 in. to 0.1 in. or more, as desired; any further 

 motion exceeding the interval to which the setting has been adjusted 

 is of course communicated to the carriage. The purpose served 

 by this preliminary movement of 47, which is not communicated to 

 44 or the ruling carriage, is to permit of the lowering and raising 

 of the ruling diamond at the beginning or end of each line. This 

 is effected by means of a second rod which passes tlirough 47, and 

 may be clamped therein at any convenient jjoint in relation to the 

 end, which pushed against a small lever. This lever lowers the 

 diamond point before the ruling of a line and raises it from the 

 plate on the return traverse as already explained. The location of 

 this rod is not seen on the plan, as it lies immediately under 44 

 and parallel with it. 



As brief reference has already been made to the operation of the 

 -diamond when ruling lines, furtlier allusion to the sul)ject may be 

 deferred until the matter is dealt with in detail. 



The foregoing brief outline of the chief mechanical features and 

 operation of the machine and ruling mechanism may fittingly close 

 with a short description of its earliest trial runs, and the subsequent 

 housing, etc., after which a more detailed account of certain of the 

 methods adopted in the construction of its more important parts 

 will be entered upon. 



The Housing of the Ruling Engine, etc. 



The provision of suitable accommodation for a machine for such 

 exacting requirements as are involved in the ruling of a dift'raction 

 grating is of some moment, especially when it is borne in mind 

 that such a machine has to run for long periods ranging from 20 to 

 200 hours at a stretch. During such intervals there must be no 

 very appreciable change in temperature of the air inmiediately sur- 

 rounding the machine, that is, no change exceeding two or three 

 tenths of a degree. Further, during the ruling of a grating the 

 machine must not be subjected to vibrations, such as might arise 

 from the proximity of trains, trams, or any heavy vehicular traffic; 

 nor yet to shocks or tremors due to the operation of other machinery 

 in the same building or immediate neighbourhood. Thus the pos- 

 sibilities to be provided for or against are by no means easily met. 



