16 Transactions of the Society. 



II. — Explanatory Notes on a series of Slides 'presented to the 

 Society, illustrating the action of a diamond in ruling lines 

 upon glass. By Prof. William A. Kogeks, F.E.M.S. 



{Read 10th June, 1885.) 



First Series. Buled previous to 1882. 



This series of slides was ruled with a knife-edge diamond. 



No. 1. Before ruling the lines on this plate, the knife-edge was 

 set as nearly parallel with the line of motion in ruling as was pos- 

 sible by sighting along the edge with a magnifying glass. The 

 lines were ruled in the direction of the >. A few lines of each 

 group were ruled with a forward motion of the diamond and the 

 remainder with a backward motion of the diamond. Between each 

 group the angle of inclination was changed. It will be seen that 

 the last four lines of the last group show a decided improvement in 

 quality. 



No. 2. In this plate successive trials failed to give any decided 

 improvement until near the end. In the last three or four groups 

 the forward motion gave a heavy line with a pretty sharply defined 

 groove near the middle of the line, while the edges are well defined 

 by finer lines. When lines of this character are obtained, the dia- 

 mond may be considered to be nearly in the best adjustment. The 

 backward motion with the same pressure gave fairly good fine lines. 



No. 3. This plate was ruled with the same setting as No. 2, but 

 with heavier pressure. The lines when first ruled were very 

 beautiful. After several days, the exact number being unknown, 

 the first band exploded and the remaining lines took on the form 

 of a strand of rope. The pressure of the diamond upon the glass 

 was evidently too great, producing lines which remained in a state 

 of tension until the rupture took place. 



No. 4. Lighter pressure than in No. 3. Heavy lines retain 

 their form and fine lines fairly good. 



No. 5. Backward motion of diamond with the same pressure as 

 the heavy lines of No. 4. A very curious specimen. Cover 

 broken. 



No 6. Windrows of fine particles of glass. A sHghtly different 

 inclination of the diamond from that with which No. 5 was ruled. 



No. 7. Many trial plates intervene between No 6 and No. 7. 

 Various settings of the diamond were tried for the purpose of obtain- 

 ing tolerably heavy lines, which should present nearly the same 

 appearance after the surface of the glass was sharply rubbed in the 

 direction of the lines as when fresh from the diamond and undis- 

 turbed. It must be understood that there is not one case in a thou- 

 sand in which the line appears as well after the surface of the 



