a UNIFORMITY OF NOMENCLATURE IN OBJECTIVES. 137 
known and is undisputed. Among other people one-fourth of an 
inch is less than four-tenths and more than one-fifth ; but among 
microscopists it may often be more than the first or less than the 
last. An indefinite number of figures might be published to prove 
or illustrate this irregularity, the writer having been particularly 
interested in making and recording these comparisons for more 
than a dozen years, and Messrs. Bicknell, Biscoe, Higgins, Cross, 
and many others having been especially interested in the same 
study ; but it is idle to prove what everybody knows and admits. 
So familiar have some of these apparent errors become by use, and 
good usage too, that they have been often accepted as estab- 
lished, even one of the latest authorities * stating the power of 
the one-fourth-inch objective five times as high as that of the one- 
In the early days of the compound microscope as a really useful 
instrument, we find microscopists wishing that microscope makers 
would “grind their glasses to some settled standard.”+ We are 
willing to be more reasonable now, or else the conditions stated 
| have become more difficult. We do not desire, nor consider it 
practicable that the opticians should make all their combinations 
of certain definite and conveniently graded powers ; but we do pro- 
pose so to name our powers, if we can, that each number shall 
Stoup together all those powers of which it is the nearest and best 
description. 
| Makers would doubtless be considered as doing a favor to those 
who use their instruments if they would, after finishing lenses, care- 
fully estimate their powers and name them by the fractions most 
nearly representing those powers. But even if this were done, and 
much more now when this is certainly not done, or nót done upon 
such a uniform plan as to be satisfactory, microscopists should 
always reëxamine their lenses in order to be definitely informed 
in regard to one of their most important properties. 
The easiest method of examining the magnifying power of an - 
_ objective, by measuring the image (of a known object) which it 
lend at a standard distance (now ten inches), was as well under- 
: me a hundred years ago as now; a lattice of fine silver wire 
ee human hair, or a scale ruled on glass, being used to measure 
Se are ee ty Sa 
nes 
* Sufolk, Microscopical Manipulation, London, 1870. 
f Bakeron Microscopes. London. 1742. 
