20 Transactions of the Society. 



No. 12. With one exception tlie only ruling producing circular 

 chips ever obtained. 



No, 13. Examine the line at the bottom of the groove of the 

 fine Knes. This line is a real groove in the glass. 



No. 14. Very deHcate threads thrown off from heavy lines. 



No. 15. Both threads and chips from the same diamond. 



No. 16. A second instance of a local explosion. Examine the 

 delicate threads beyond the ends of the lines. 



Fourth Series. Buled in 1885. 



No. 1. Plates Nos. 1, 2, 3, 4, and 5 of this series furnish positive 

 proof of the fact that the lines which appear to be the most perfect 

 in form are not produced by grooves cut in the glass, but by 

 windrows of minute particles of glass thrown up by the ruling 

 diamond. In this plate the real groove is about 2 • 2 yu- in width, 

 the space between one edge of the groove and the furrow is about 

 1 • //-, and the width of the windrow is between 0*1^ and • 2 /ut. 



No. 2. The windrow of glass is a little better defined on this 

 plate than on No. 1, being if anything a shade narrower. The 

 Hues on Nos. 1 and 2 were ruled on the under side of the cover. 



No. 3. This plate was ruled with exactly the same pressure of 

 the diamond as Nos. 1 and 2, but the lines are upon the slide. 

 Before the disturbance of the surface the lines presented precisely 

 the same appearance, and had the same width as in those two 

 plates. After rubbing the surface of the glass at right angles to 

 the lines, the windrows were completely broken down and the 

 particles of glass were scattered over the entire surface, clinging to 

 the surface in the grooves only. Doubtless, the greater part of the 

 windrow was entirely removed from the surface by rubbing. 

 That the windrows are not entirely broken down, however, is 

 evident from the fact that the extreme width of the lines is the 

 same as before — viz. about 3 ' 2 /a. 



No. 4. In this plate the lines, after being ruled, were examined 

 carefi4lly, and were found to present the same appearance as in No. 3 

 before cleaning. Their width was also found to be the same. 

 The lines were then rubbed crosswise when their appearance was 

 precisely the same as in No. 3. They were then scoured by 

 rubbing with a cleaning powder in the direction of the lines. The 

 first thorough cleaning removed only about two-thirds of the debris. 

 After a subsequent and more thorough cleaning they were covered. 

 The width of the lines is now the same as the width of the groove 

 after ruling and hefore cleaning — viz. about 2'2 fi. 



No. 5. In order that it may not be said that the Knes upon the 

 cover-glass have a different width from that upon the slide, the 

 lines of this plate were ruled upon the slide, and the surface was 



