170 J.J. Woodward on Nobert’s Test-plate. 
of Powell and Lealand, with which lens I secured the best 
definition, the lines of the fifteenth band were distinctly re- 
solved. In the higher bands spurious lines, fewer in number 
than the real ones, were seen. The nature of these lines was 
conclusively shown by a count. With the paper, I sent to the 
editors a series of photographs, taken by Brevet Major E. Curtis 
at the Army Medical Museum, which showed in a satisfactory 
manner precisely what had been done. Upon the basis of these 
experiments and photographs, I expressed the opinion, that, 
those who had previously supposed they had seen the true 
lines in higher bands than the fifteenth, had been misled by 
the spurious lines described ; an opinion which has been still 
further strengthened by subsequent experiments with lenses 
by the maker whose objectives were supposed to have been suc- — 
cessful. 
During March of the present year I received from Nobert 
another nineteen-band test-plate made differently from any I 
have as yet seen in this country. The glass cover measures 
but the ,4,th of an inch in thickness, and this is cemented to 
a glass circle the 1,th of an inch thick, supported on a strip | 
of brass. The new plate, therefore, permits the use of lenses of 
the highest power, and may be illuminated by extremely oblique 
light or by an achromatic condenser of very short focus.  % 
I found, nevertheless, that the ,.th of Powell and Lealand 
would go no further on this than on the former plate and their 
;;th gave the same result ; it would not resolve the sixteenth 
stage. 
I send two prints on glass, of which, the first shows the 16th, _ 
17th, and 18th bands, nae he Agar resolved. The second 
shows satisfactorily the 19th band only. These pictures should 
