l888.] NEW-YORK MICROSCOPICAL SOCIETY. 83 



tained by having different portions of different degrees of 

 brightness. 



Photomicrograph No. i is of a Test-Plate having 19 bands — 

 said to have bands ranging from 5,000 lines per inch, to the 

 i8th, which has 120,000 lines per inch. The 19th band only 

 has 50,000 lines per inch of the same depth of cutting as the 

 i8th band. These bands all having been resolved, new plates 

 were ruled, having finer bands. 



Photomicrograph No. 2 is of a Test-Plate with bands in the 

 metric measures. In one important respect the system of ruling 

 on this plate was modified. Each band, for a short portion of 

 its length, was only ruled with one-half of the number of lines 

 in the rest of the band. The label sent to put on this No. 2 is 

 probably not the proper one, as the bands do not agree. 



Photomicrograph No. 3 is of a Test-Plate having 23 bands: 

 the highest having, it is said, 200,000 lines per inch. The rul- 

 ing is very delicate, and the lines quite shallow, as must be the 

 case. Mr. Fasoldt says twelve persons have seen the lines in 

 the last band, under his method of illumination, and with a 

 Bausch & Lomb t^ objective, N. A. 1.35 (?). 



The first evening I looked at the Test-Plate, I saw the lines 

 in the band of 130,000, clear and well defined, after the instru- 

 ment was focussed. Unaided I was unable to go beyond the 

 90,000 band. This trial was made after a railroad trip of ten 

 week-days and five nights. The vision was not as acute, and . 

 the touch of the fingers was not as sensitive as usual. In about 

 a week afterwards, at a second trial, I saw all of the lines to the 

 160,000 band, which I was unable to resolve. The 170,000 and 

 180,000 bands I did not resolve, but the 190,000 band came 

 out sharp and clear. This was all I could do at that time. The 

 delicacy of focussing is probably as difficult as the discerning 

 of the lines. 



Photomicrograph No. 4 is of a quadruple ruling, the central 

 bands being 80,000 per inch. When both sets of lines are il- 

 luminated the spectra produced are gorgeous. Mr. Fasoldt 

 states that rulings, which do not produce spectra, are not re- 

 solvable. And he discards such rulings, as the lines are ruined. 



These rulings are of very great interest to the microscopist, 

 as a measure of what can be done by different methods of il- 

 lumination. After many trials by transmitted light, the band of 



