On Uniformity of Nomenclature in Objectives. 15 
covered it magnifies rather less, at covered rather more, than the 
Powell and Lealand y^th.” Further, “its equivalent focal length 
at uncovered is therefore y- ft th, very nearly.” The same is repeated in 
the ‘American Naturalist’ for April, 1872. Why does Dr. Woodward 
still persist in calling an objective a 1 1 e th, which he has repeatedly 
admitted to be higher than a y^th, and which Mr. Charles Stodder 
writes he has “ascertained to be a y^th ” ? On page 30, vol. vii., 
of this Journal, Dr. Woodward has published a table of powers in 
decimals of an English inch. In this table he gives the dry Powell 
and Lealand T ^th at uncovered point the expression • 0623. That 
is all right as far as the dry front is concerned, but if the reader 
wishes to know the power of the immersion front at its lowest 
power he may substitute the decimal '0533, and he will be not far 
from right. 
I can still furnish further evidence to prove my position, but do 
not think it at all necessary. The members of the Eoyal Micro- 
scopical Society can count the fines in the glass positives, which I 
believe they have duplicates of, and satisfy themselves of the truth 
or otherwise of my statements. I counted the lines with a low 
power, 4-inch, and positive eye-piece, and was very careful to count 
the same part of the same frustule in both cases. 
Dr. Woodward brought out his tables in “ fair play ” to Messrs. 
Powell and Lealand, and undertook to show that the objective was 
not of higher power than its denomination. I write this com- 
munication in order to show that the immersion front made it of 
much higher power, and those makers whose objectives are correctly 
marked, or nearly so, would not have “ fair play ” if their work was 
tested against this objective and its actual power not stated. 
V . — On Uniformity of Nomenclature in regard to Microsco- 
pical Objectives and Oculars. By R. H. Ward, M.D. 
The nominal focal length of an achromatic objective, as used by 
microscopists generally, represents its amplifying power as actually 
used in the compound microscope. Even the equivalency in ampli- 
fying power with a single lens of the same focus is no longer dis- 
tinctly realized, while the size and appearance of the combination, 
its working focus, angular aperture, and microscopical efficiency, 
are not even hinted by 7 the figures used. The nominal focus repre- 
sents the magnifying power and those properties dependent on it. 
Like other measurements, these must be stated by comparison with 
known standards. To use diverse and unknown units of measure- 
ment in cases designed to be compared with each other is simply 
VOL. VIII. c 
