182 
Notes. 
[March, 
Dr. F. Hulwa (“ Gesundheits-Ingenieur ”) proves that the 
water of the Oder, after receiving the sewage of Breslau, is 
purified by the oxygen of the atmosphere and the aCtion of vege- 
tation. Fourteen kilometres below Breslau the sewage matters 
can neither be detected chemically nor microscopically, and the 
water was of the same quality as above the town. 
Dr. E. von Raumer shows that the special funaion of lime in 
vegetation is the elaboration of material for increasing and 
strengthening the cell-walls. Magnesia, on the other hand, me- 
diates the transportation of starch, and subserves the formation 
of chlorophyll. 
Mr. J. Gunn, F.G.S. (“ Geological Magazine ”) contends that 
the levelling of mountain ranges may be the cause of warmth ot 
climate, just as their elevation is productive of cold. 
Certain experiments made by Prof. Bunge (“ Zeitschrift Phys- 
Chemie”) upon Entozoa tend to show that the sources of mus- 
cular power in animals do not exclusively reside in the process 
of oxidation, but in the decompositions which take place in their 
food. Hence the less body-heat is required, the less is the need 
for oxygen. 
Respecting the resolution of diatom markings Professor Abbe 
writes “ All speculations as to the true structure of even 
Pleurosigma angulatum, so far as they depend on microscopic 
vision, are mere phantoms, castles in the air. No human eye 
has ever seen, or ever will see, the complete diffraCtion-speCtia 
arising from a structure of this minuteness, nor will any micro- 
scope ever show an enlarged copy of it, so long as the speCtra 
cannot be observed in a medium of at least 5 '° refraCtive index 
and by an objective of 5-0 numerical aperture,* which, as far as 
our present knowledge goes, is an impossibility. The micro- 
scopes of the present day admit relatively a small central portion 
of the whole diffraCtion-speCtrum of the valve,— i. e., the incident 
beam and the six speftra of the inner circle. But this portion 
is also yielded by a multitude of other objeas which are endowed 
with an alternation of superficial or internal molecular struaures 
which cross each other in two differeat direaions at an angle of 
6o°. Such struaures may be formed in various widely different 
ways ; it may be by rows of spherules or other prominences of 
any shape whatever ; rows of internal vacuoles of any figure, or 
the mere internal alternations of molecular aggregations within 
a perfeaiy transparent and smooth silica film. And yet all these 
yield with central light the identical circular field of the angulatum 
valve, even to the most minute particular. But although these 
speCtra are identical as far as the six inner speCtral beams are 
* Half the sine of the angle of aperture multiplied by the index of refrac- 
tion of the medium in which the objedt is viewed. 
