1877.] Microscopy. 317 
instruments exhibited at the opening of the exhibition. [It was cer- 
tainly present in the Rochester instruments exhibited during the sum- 
mer.]. This would give the priority in this important improvement 
clearly to Mr. Zentmayer. 
The so-called student’s stands are mentioned with the intimation that 
too many of them are unfit for use, and with an earnest appeal for better 
workmanship in their construction. 
Objectives are discussed without restriction to those exhibited at Phil- 
adelphia. Indeed it would be hardly possible to say anything compre- 
hensive about them otherwise, since Mr. Tolles’ work could not be over- 
looked in such a discussion. 
Mr. Wenham’s patent lenses, in which corrections are obtained by a 
single flint lens, were considered to give great promise, but to be so un- 
successfully mounted as to compel a suspension of judgment in regard 
to them. Mr. Crouch’s lenses were considered excellent and exceed- 
ingly fine for their cost, though without extraordinary optical qualities, 
strikingly resembling in corrections the Wenham lenses. Beck’s lenses 
Tetain their character for excellent optical properties, being as nearly 
achromatic as possible without aiming at maximum angle. Their mount- 
ing, however, is poor in design and execution. The new Powell and 
Lealand one-eighth ranks highest of all foreign objectives yet seen, and 
marks a new era in English microscopy. It gives a bluish-green light, 
with sharp and accurate definition, and a good image to the edge of the 
field. The mounting is superb, and the American [Tolles’] plan of trav- 
ersing the back combination is adopted. 
The German objectives are not commended, the lower powers being 
judged unfit for use, and the high ones to fail in comparison with our 
lower powers. The brass work is considered inferior, and the lenses 
show a want of finger skill. 
American lenses he speaks chiefly of those by Mr. Tolles, because 
those of other makers have disappointed him. He considers that there 
are greater optical possibilities in Mr. Tolles, in the construction of 
lenses for the microscope, than in any other maker. His lenses are 
often thought faulty because not understood. - No two of them are alike, 
but this is due, he is satisfied, not to unequal execution, but to a special 
change in each case to obtain a higher degree of some particularly 
desired quality. Neither are penetration and resolution incompatible to 
the extent claimed by the theorists. Some of Mr. Tolles’ lenses of ex- 
treme angle have a penetration so extraordinary that they form the best 
lenses known for histological work by central light, showing details with 
a brilliancy not otherwise seen. A recent Tolles one-tenth has the 
same power as the new Powell and Lealand one-eighth, but with clearer 
and more brilliant definition and greater penetration. It adopts the 
[Wales’] method of adjusting for wet and dry by the screw-collar, while 
the one-eighth has a separate front, a less convenient plan. 
