18 Transactions of the Society. 



No. 13. This plate was ruled both with forward and backward' 

 motion of the diamond, and with varying pressure. Several plates 

 intervened between this one and No. 12, in which the slightest 

 possible adjustment of the diamond was made. 



No. 14. Up to the present time (1881) this is the most perfect 

 plate I have ever produced. I do not at first expect to be believed 

 when I say that what appears to be the edge of the groove at one 

 edge of the line is a windrow of glass turned up from the groove. 

 Careful inspection, however, will show a clear space between 

 the real edge of the groove and the jet black line. That is, one 

 sees two faint lines which are the edges of the groove and the 

 black line on the right, which is really a windrow of particles of 

 glass. In a later plate I shall prove that this explanation is the 

 true one. 



No. 15. A test-plate for the limit of vision. Bands of fine lines 

 following a heavy line. The lines of the last two bands invisible, 

 but brought out clearly in a duplicate plate mounted in Professor 

 Hamilton Smith's new medium. It should be said that the lines 

 of this plate are far less sharply defined than when first ruled. 



Second Series. Ruled in 1882-3. 



No. 1. This plate preceded by several trial plates. 



No. 2. Varying pressure of diamond. Sweating has taken 

 place in this plate and in the preceding one. Attention is called to 

 the fact that the sweating does not usually take place near closely 

 ruled bands of lines, especially if the lines are heavy. 



No. 8. A remarkable specimen of lines formed by furrows of 

 glass. The lines are mounted lengthwise of the slide. Attention 

 is called to the arrowheads at the end of each line and to the 

 deposit of a particle of glass on every line a little distance from the 

 end. It will be seen that the sweating upon the surface occurs at 

 a considerable distance from the bands. 



No. 4. Another illustration of the fact that sweating does not 

 usually take place near heavy ruled lines. The lines of this plate 

 are filled with graphite. 



No. 5. Upon the whole this plate is the best illustration yet 

 obtained of the action of a perfect ruling crystal. The curved lines, 

 which are formed by the intersection of straight lines, take the 

 graphite almost as well as the straight lines. This plate should be 

 examined under a 1/4 or 1/5 in. objective. 



No 6. This plate of squares 100 to the inch is a good illustra- 

 tion of a good groove well filled with graphite. 



No. 7. In this plate the graphite presents a granular appear- 

 ance, which is often seen when ruled lines are repeatedly filled with 

 graphite. When the lines of this plate were first filled, directly 



