ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
133 
Aquarium Filter.* — Prof. R. v. Lendenfeld has devised a simple 
method for filtering sea water in an aquarium without pouring out the 
water and without disturbing the sand layer at the bottom. 
In the aquarium A 2 (fig. 25) which is closed with a cover, the level 
of the water stands at W. For freshening the water air is introduced by 
the tube L u through the hole L in the cover, and passing down the thin 
tube L u R rises in bubbles from the end 0. The end of the thin tube 
Fig. 25. 
LuR passes up into a wider tube W r, which after a. double bend dips 
into the filter F. In this tube the air-bubbles rise and carry with 
them water which enters at its lower end and flows out at E into the 
filter. 
By regulating the stream of air it is possible to regulate the amount 
of water so that the filter shall always be nearly full, but not run 
over. 
Ink-Crystals.f — Dr. E. Trouessart says that ink-crystals can be pro- 
cured by allowing a drop of ink to dry on a slip of glass, and be seen 
by powers magnifying from 50 to 200 diameters. Different inks give 
somew r hat different crystals, but the chemical composition of none of 
them is yet exactly known. 
