TRANSACTIONS OF SECTION A. 



471 



To avoid any sbock in starting or reversing, the cams e^, 6 on D and B, which 

 are in reality the halves of a large pair of teeth, have their curves so calculated 

 that when they engage, D communicates uniform angular acceleration by roUmg 

 cont'act to B, until the velocity of the latter is to that of the former as the pitch 



Fig. 4.— Showing the operations performed by the driving machinery while ruling 

 one line of the dift'raction grating. 



circles of D and B, when the cams separate, leaving the ordinary teeth m gear. 

 There are of course a similar pair of cams on B' and the opposite side of D. 



Cams of the same type are used for starting the intermittent motion which has 

 tobegivento the adjustable crank, Q, fig. 1. ^ , -^ , . x. 



The whole of the mechanism has worked without any kind ot hitcli Irom the 



beginning. 



As to the results obtained, the author had hitherto, on account of not having a 



Fig. 5. 



satisfactory motor, confined himself to ruling coarse gratings of from 2,000 to 4,000 

 lines per inch, the largest which he had rided up to the present time bemg about 

 5| inches square, with about 2,800 lines per inch. This grating gives very fair 

 results, considering that it is ruled on plate glass not specially worked, but only 



