678 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
He considers that Zeiss’ water-immersion system D* is usually the best 
to use for the observation of living creatures in water-chambers. In 
many such cases, however, the desideratum is not so much a lens of 
powerful resolution and high magnification as of extended field of view 
and deep penetration. His new objective is constructed to meet this 
want, and he names it the “ Pianktonsucher.” 
The Pianktonsucher has a front focus of 35 mm., a working distance 
of 36 mm., and a numerical aperture of 0*11. For a tube-length of 
160 mm. and Zeiss’ Huyghens’ oculars 1 to 5, the following values are 
obtained for the diameter of the objective field and for the magnifi- 
cation : — 
Huyghens Ocular. 
Objective Field, 
mm. 
Magnification. 
1 
3-5 
25 
2 
3-3 
35 
2* 
4-2 
35 
3 
2-4 
50 
4 
2-0 
60 
5 
1-7 
80 
In consequence of the use of the new Jena glasses, which after many 
years’ experience have proved extraordinarily durable, a very good cor- 
rection-position could be given to the system. The image is completely 
plane and free from astigmatism quite close up to the periphery, even 
when ocular 2* with its extended view-field is used, so that adjustment 
affects the whole view-field uniformly. As the interference of the raj- 
pencils is almost apochromatic, the images display a clean-cut distinct- 
ness. In order to be able to carry on observations in water, the lenses 
are fastened on the end of a cylindrical niokelled brass tube, so that 
entry of the water is impossible. 
In order to secure small creatures on the floor of the water-chamber, 
three narrow glass bars are cemented on to the floor, and a cover-glass 
placed on them (below the water-level), so that the objects are enclosed 
in a thin stratum, which stratum can be explored without altering the 
adjustment of the objective. 
(3) Illuminating- and other Apparatus. 
“Newtonian” Universal Science Lantern (Ives and Newton’s 
Patent). — This lantern has been devised with “a view to producing an 
instrument which shall be extremely portable and which shall yet be 
capable of producing, with a minimum of trouble and rearrangement, 
most of the experiments required by science lecturers. As shown in the 
illustration (fig. 118), it is fitted with lantern-slide front, microscopic 
attachment, and spectroscopic front. The lantern is so fitted that any 
one of the three fronts can be exchanged for the other by simply sliding 
the front from the centre to the one side or the other as may be required. 
The first front is for showing the ordinary slides or diagrams, and 
comprises a 4-in. double condenser and 8-in. best double achromatic 
front lens, exhibiting slides as well and clearly as any lantern that is 
made. 
The second front is a Microscope attachment, and is of more interest 
to the readers of this Journal, perhaps, than the other parts of the iustru- 
