SUMMARY OF CURRENT RESEARCHES RELATING TO 
24 1) 
MICROSCOPY. 
«. Instruments, Accessories, &c .* 
C2) Eye-pieces and Objectives. 
“On a new System of Erecting and Long Focus Objectives.” t— 
M. L. Malassez, after referring to the advantage of erect images and long 
focal lengths, when delicate dissections havo to be made, exact measure- 
ments determined, &c., writes: — 
“ For these purposes we have already at our disposal the simple lens 
or the doublet, the Brucke lens, and the ordinary compound Microscope 
furnished with erecting apparatus. These instruments are excellent in 
certain cases, but are certainly unsatisfactory in many others. Thus, the 
simple lens and the doublet do not give sufficiently strong magnifications 
with foci sufficiently long, and, in making use of them, it is necessary 
to bend over the object to be examined in a very uncomfortable way. 
The Brucke lens possesses the advantage of having a very long focus, 
but the magnification which it affords is not very considerable. The 
Microscope itself gives all the magnification desired, but as soon as this 
becomes at all considerable, the focus is very short, and there is no room 
for manipulation. 
I have devised a new system of objectives, which gives the best 
results. Adapted to the ordinary Microscope, the objective gives at once, 
without erecting apparatus, an erect image of the object examined. Its 
focus is very long, as long as could be wished. One of them has a focus 
of 7 cm., while it gives a true magnification of 30 diameters with a No. 2 
eye-piece of Verick, and a tube-length of 16 cm. I have made some 
which had foci much longer, reckoned by metres instead of centimetres. 
With these it was possible to see with the Microscope objects placed at 
the other end of the work-room, or even objects more distant still, such 
as houses and monuments at a distance from the window. However, as 
we lose in magnification and light what we gain in length of focus, it is 
of advantage to limit this as much as possible. 
These new objectives possess the further advantage of considerable 
penetrating power, i. e. it is possible to vary the focus without losing 
the object. The one mentioned above has, for instance, a penetration 
of 2 to 3 millimetres. It is possible to get more, but it is necessary to 
limit it, for it would be at the expense of the defining power, i. e. at the 
expense of the clearness of the images. 
The field of view is sufficiently large ; that of the objective already 
taken as an example is from 8-10 mm. in diameter. With it microscopic 
images are obtained perfectly plane. The field is, of course, enlarged 
as the magnification is reduced. The device by which I have obtained 
the two principal properties characteristic of this new- system of 
objectives, viz. the erection of the images and the indefinite length of the 
foci, is as follows : — 
The different lenses composing the objectives really form two distinct 
* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 
minating and other Apparatus ; (4) Photomicrography ; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. 
t Arch, de Med. Exper., i. (1889) pp. 449-54. 
