90 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Eousselet’s Simple Tank Microscope. — Mr. C. Koiisselet exliibited 
at a recent meeting of the Society a small tank Microscope (fig. 6) 
designed for the purpose of rapidly looking over pond water and weeds 
collected at a day’s excursion and placed in a small parallel-sided 
window aquarium. 
One of Zeiss’ aplanatic lenses is carried on a jointed arm, which 
moves parallel to the side of the tank, and the lens is focused by means 
Fig. G. 
of a rack and pinion, the whole being fixed to the upjier left-hand corner 
of the tank by means of a screw clamp. 
The following points, Mr. Rousselet considers, will recommend them- 
selves to those who are in the habit of looking at their captures with 
the pocket-lens in the ordinary way : — 
When an object of interest is found it can be followed with the 
greatest ease and taken up with a pipette, both hands being free for this 
operation. It frequently happens that a minute object is lost simply 
by removing the pocket-lens for an instant to take up the pipette ; in the 
above apparatus the lens remains in the position in which it has been 
placed. The definition of these aplanatic lenses is excellent ; the lowest 
power has enough working distance to focus through tanks of moderate 
size, and the magnification (6 diameters) is sufficient to permit of the 
identification of all ordinary rotifers, and anything uncommon or new 
is at once recognized. Such delicate creatures as the Floscules, which 
are all but invisible with the ordinary pocket -lens, are seen without 
difficulty, and the whole contents of the tank can be ascertained with a 
great saving of time. 
