358 THE AMERICAN MONTHLY [Nov 



which serve to correct its movements to correspond 

 with the inch or millimeter to be ruled. In this case <me 

 revolution of the screw moves the wedg-e so that its lateral 

 displacement is equal to one one-thousandth of an inch. 

 This lateral displacement of the m<)ving- wedg-e operates 

 on a block of brass resting- on three points projecting^ from 

 its base. By the side of this block of brass is operated 

 the diamond carrier. The points of contact for the entire 

 system of screw, wedge, block of brass and diamond car- 

 rier, operate upon pieces of plate glass — plate g-lass strips 

 where contact points move on wedge and block, and plate 

 g-lass bed resting- on an iron base, which supports the 

 long^itudinal and lateral movements of the block of brass 

 and the diamond carrier. This give a smooth and accu- 

 rate motion to all the working- parts, which could be other- 

 wise obtained only by expensive and carefully polished 

 steel surfaces. 



This is a g-eneral description of the first working- model 

 so far as is known, using the principle of the wedg-e as a 

 means of adjustment and correction, and of imparting^ the 

 motion of a decreasing- g-ear from the screw which is nec- 

 essary for such work. A considerable motion of the 

 screw is thus g-iven for minute divisions, thereby ensur- 

 ing- uniform and accurate ruling-s. 



The device for carrying the diamond, as first used, was 

 a single carriag-e. moved back and forth by hand along- 

 the glass bed plate, and held in its i)lacc to the brass 

 block by means of contact spring-s. Afterwards for con- 

 venience, a triple link carriage was made, that is, three 

 separate parts hung- by three trunnion points of hardened 

 steel accurately turned. Though much more scientific, 

 and easier of use the results, up to thirty or forty 

 thousand lines, was hardly worth the trouble of its 

 construction, save the chance of any disturbance of the 

 diamond point by accidental handling of the diamond 

 during- ruling. 



With a little more trouble the entire arrangement 

 could be easily adjusted to become entirely automatic in 

 its movements, whereas in the present model the move- 



