WOODWARD ON NOBERT's TEST-PLATE. 231 



cognised by their appearance, as well as by their number. 

 They are j)ale and broad, and their margins quite unlike the 

 sharp, clear edges of the real lines ; but in the microscope, 

 even with the -^oth of an inch, they look to the eye so like 

 the real ones as readily to deceive. It is these spurious lines, 

 no doubt, that Mr. Stodder saw in the 19th band, with 

 Tolles' immersion, -^th. 



In order that no doubt of the character of these lines 

 might remain, additional photographs have been prepared of 

 the iJ^th, 13th, and 14th bands, with the illumination 

 so arranged as to produce spurious lines. One mode of 

 illumination gives lines which do not exceed sixteen in 

 number in any of these bands. The other gives about 

 twenty-five lines for the 12th band instead of forty, which 

 is the real number. The character of the lines in the last 

 two photographs is quite similar to that of the lines shown 

 in the photographs of the 16th, ITth, 18th, and 19th bands. 



The 15th band is therefore the highest which I have 

 resolved with the glasses at my disposal. It corresponds 

 to the last band of the thirty-band plate, and I believe the 

 true lines have never been seen in it before. 



It is probable that if opaque markings of still greater fine- 

 ness could be produced, the same objectives would resolve 

 them, but with the superficial scratches on glass afibrded by 

 Nobert's plate this result is not possible. Nevertheless, the 

 opinion may be expressed that the lines of the last four 

 bands have been ruled as Nobert claims, and that with lenses 

 of better definition they could be seen. 



I may here mention that one of the photographs of the 

 I6th, 17th, 18th, and 12th bands, showing spurious lines, was 

 made at the museum by Dr. Curtis, with a Wales ^th and 

 amplifier, a few months previous to the other photographs. I 

 supposed at the time, and, indeed, until qiiite recently, that 

 the lines shown in the 16th and 17th bands by this photo- 

 graph were the real ones, and accounted for their being too few 

 in number (the 16th counting only thirty-seven, the 17th only 

 forty, lines) by supposing that the whole of each band was not 

 to be seen in any one position of the focal adjustment. I have 

 since learned more of the appearance of spurious lines, and 

 recognise that all the lines shown in this earlier photograph 

 were such. 



I learn from Dr. Barnard that Nobert, to whom it was 

 shoAvn by Eulenstein, accounted for the small number of 

 lines in this photograph by supposing that Dr. Curtis had, by 

 mistake, cojHed the 12th, 13th, 14th, and 15th bands. I can 

 assure the distinguished optician that we have made no such 



