406 J. J. Woodward—Nomenclature of Achromatic 
EXPLANATION OF PLate IX. 
Figure A. Lateral view of the larval young in the first stage observed, enlarged 10 
diameters, 
‘“  B. The same in a dorsal view, the abdomen held horizontally. 
“ @. Antennula, enlarged 20 diameters, 
exopodus; 6, epipodus; ¢. branchie. 
‘“  E. Lateral view of the larval young in the third stage, enlarged 8 diametei 
“‘ ¥. Terminal portion of the abdomen seen from above, enlarged 15 diame- 
minal segment, enlarged 75 diameters. ; 
“_ @. Basal portion of one of the legs of the second pair, showing the epipo- 
dus and branche, enlarged 20 diameters. 
Art. LIL—Remarks on the Nomenclature of Achromatic Ubjec- 
tives for the Compound Microscope ; by Dr. J. J. Woopwarp, 
U.S. Army. 
For some years past, while most of the Continental opticians 
have continued to give arbitrary designations to their achro- 
Under these circumstances, it appears desirable to give some 
account of the principles involved, and of the practical d he 
ti be considered in their a plication, particularly et 
microscopical text-books contain little or no information on 
subject. In fact, the only scientific discussion of the me R 
with which I am acquainted is the paper of Mr. Charles 
Toss, “On the focal length of microscopic objectives. pet 
nal of the Franklin Institute, June, 1870, p. 401). ‘This pa 
' gives a b | | of 
equivalent focal lengths, and furnishes some other vale a 
ti j ee ei 
refer more than once to this excellent Pane a 
ave 10n to L . 
which the reader would do well to examine in connection 
the following remarks, 
