350 W. 8. Sullivant on Nobert’s Test-plate. 
Mr, Stodder remarks “it has been said that the resolution — 
of lines to the eye, implies the ability to count them, but this, — 
I think, is a fallacy,” and illustrates his remark by the difficuliy — 
of counting the pickets on a fence, at a given distance, The 
difficulty in both cases could perhaps be surmounted to the ex 
tent necessary, by enlarging the visual angle under which the — 
lines and pickets appear to the eye, viz: by adding to the am- — 
plification of the microscope, and shortening the distance to 
the fence. ee 
Among the highest bands of the Nobert plate, owing tothe 
want of perfect flatness of field inseparable from the best ob- 
jectives, a portion only of the width can at one time be brought 
into exact focus. If that portion, however, is measured andits 
lines resolved under a suitable amplification, the data are ob 
tained for the solution of the problem in hand, namely, the d& 
counting lines of such exquisite fineness, either the micromewr = 
or the stage must be moved, and it is next to impossible tooat ; 
struct apparatus that canbe moved atonce przco0 OAR 
bove cited 
were seen (page 99) with a } objective and under an ampli 
tion of 550 diameters foatamt 
Besides the low grade of the objective, & noteworthy tae 
in this performance, is the low amplification employed. 4 ai 
— tofore it has been found no easy task to confirm by ere 
f an inch apart, resolved by ® ws 
grade objectives, under an amplification of 6,000 iameters : 
Mr. Stodder very correctly remarks that an exact and ©" 
trollable mction in the micrometer or the stage for t 
of counting the lines of the highest bands, 1s next to 
ble. But in the mere counting of lines, 
important requisite, not the micrometer, 
simply to measure that portion of the wid 
the linescan be counted. Motion in the measumie 
rately, and thus measure the portion of the band on ne one 
req 
