410 J. J. Woodward— Nomenclature of Achromatic 
Now as these values vary considerably with the cover comec- 
tion, it is to be feared that the majority of the measurements, 
made with high powers during the last twenty years are sadly 
inaccurate. 
The difficulties in the way of a nomenclature based upon 
Magnifying power. 
Dry. Wet. “ioe 
‘Uncovered. Covered. Uncovered. Covered. 
No. 1, 225 250 0 275 
No. 2, 425 490 450 500 
No. 3, 700 900 900 1000 
No. 4, 770 910 900 1100 
No. 5, 790 930 975 1180 
Of these objectives No. 1 had but one front, the correction 
for wet being made by the cover correction; the others had two 
separate fronts, one for wet, the other for dry. io 
ow it is just in connection with these complex objective 
with double fronts or other devices to correct for wet and dty, 
that the greatest diversity of nomenclature exists. In one quar 
ter it is claimed that the system should have two names, one 
from the magnifying power at uncovered dry alone. It is @¥F q 
‘yin pe 
dent, however, that neither of these plans has any prete “ 
rally,—not always,—the angle at the correction for thi 
the greatest angle attainable by the combination, which ae “ 
7 
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