668 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
and shows plainly the advantage of its enormous aperture. It is a 
triumph of the optical firm which produced it. 
But I would hasten to say (1) That I would not trust a single result 
produced by its means, when oblique light in one azimuth is employed, 
especially with the chromatic flint condenser provided by the firm of 
Zeiss for its illumination. It is fatal to its truth. We can absolutely 
get almost any desired result with it. It is a very optical witch of 
Endor for calling up ghosts and ghostly visions. 
(2) I did not use with it the condenser provided for its illumination. 
This lias a dense flint front lens, and an enormous amount of aberration. 
It breaks the delicate balance of the beautiful objective, and is to it, in 
critical hands, worse than the chromatic Abbe condenser used upon flue 
apochromatic objectives of lower aperture ; and naturally 
(3) I could only successfully employ the fine achromatic condenser 
of Powell and Lealand with the great numerical aperture of 1 ■ 4. This, 
of course, could not utilize all the immense aperture of the lens, but 
when its full cone was employed with its relatively great aplanatic 
aperture of 1*1, it yielded results that to a student of delicate diatoma- 
ceous images was a vision of beauty indeed. 
And it could do more than this with an apochromatic or even an 
achromatic condenser of its own aperture. 
But now comes the pragmatic question, which we are bound to ask, 
“ What does this objective contribute to the practical work to which, 
for the attainment of the highest results, the Microscope must be 
applied ? ” 
I say at once for the amateur and the lover of splendid images the 
objective may be a delight. 
But I have pointed out before that even immersion objectives, though 
they have a great, have nevertheless a very limited, use in strict bio- 
logical inquiries of a certain kind. 
This is true of water ; it is doubly true of oil. If we are examining 
minute life under a limited cover, the fluid above, between the lens and 
the top of the cover-glass, will ultimately, in following the travels of 
the living creature, be caused to mingle with the fluid between the cover 
and the slip, and so destroy the work. 
But in spite of this, immersion and especially homogeneous 
objectives have an enormous value for experiments in control and 
comparison. 
But with the new lens of this great aperture, not only have we to use 
flint covers, specially and expensively ground, and flint slips, but of 
course we have to employ a dense mounting medium absolutely fatal to 
all organic tissues. 
Flinty and carbonaceous animal and vegetable products, however 
fine, may be examined by its means ; but the cell as such, to say nothing 
of the living cell and unicellular organisms, can never at present be 
subject to its optical analysis. 
Now it must not be supposed that this fact was not fully known to its 
accomplished makers when they devised and sent it out ; that would be 
an error. But in our inquiry as to the influence it will exert upon the 
special work of the Microscope in unravelling the structure and deport- 
ment of animal and human tissues it is a great factor. 
