ae oS ee 
_ through a small achromatic lens of long focus, was effective i 
W. S. Sullivant and T. G.Wormley on Nobert's Test Plate. 13 
years since Messrs. Harrison and Sollitt published (Microscop- 
ical Journal, vol. ii, p. 61, 1854) their measurements of the strie 
of several dia toms, assigning to Amphipleura pellucida strice 
as close as the ¢sglsa5 tO rsa)507 ; of an inc ese measure- 
ments have recently been Rose ad with exactly the same 
results, by Mr. Sollitt alone (Mic. Jour., vili, p. 51, 1859) who 
a expresses the opinion that stria as close as the 
the number of its zealous devotees—that so few experiments 
have been made, bearing on this interesting point. 
Asa contribution toward that object, we propose to offer pre- ' 
aie oo era of rare actions in al res 
besides {3 —_ and ;},ths of other eminent opticians, both English 
and American; also a solid eye-piece eee by Tolles, and 
an hades cobweb micrometer of Grunow’s accurate work- 
manship. Smith-and Beck’s stage scales fartnied the —— 
for fixing the micrometrical values of the eye-pieces. 
of Tolles’ amplifier, an achromatic concavo-convex ear between 
the objective and the eye-piece, an amplification (by the ‘star 
dard of 10 inches) as high as 6000 times was obtained. Th 
” 
high amplification, with sunlight variously applied after passin 
Bia a? 
resolution, and essential to the distinct counting under the mi- 
crometer of the lines of the test plate. The test plate used e 
sisted of 30 bands of lines, each band varying but litt 
the 5.2,; of an — in width, and having its lines a un 
tance a one end of the plate is engraved by. 
parts of the Paris line, the distance epartrol the 
the first band, and thence on, the distance betwee 
ae me omipetdaug sn hes olu: 
