CORRESPONDENCE. 
i° 7 
EDITORIAL NOTES. 
The Rev. Hilderic Friend, F. L. s. informs us that he will be 
in London the last week in January and will have one night at 
liberty for a lecture. Secretaries of societies may obtain par¬ 
ticulars and terms from the lecturer, 7 Fern Bank, Cockermouth, 
Cumberland. We have a list of 14 lecturers (illustrated with 
hand-painted transparencies) any one of which Mr. Friend is 
prepared to deliver. 
We must not allow this issue to go to press without some slight 
tribute to the great scientist who has passed from our midst, and 
we only regret that we cannot give a more extended notice, for 
Professor Tvndall was in every sense of the word a teacher of the 
* J 
people, his writings being possessed of a lucidity and far-reaching 
conception that entitle him to rank with Darwin and Huxley as an 
exponent of that newer Science to which the latter half of our 
century has given birth. 
By an advertisement elsewhere it will be seen that the Natur¬ 
alist’s Publishing Company, of Birmingham, are commencing 
operations as scientific booksellers. We are informed that they 
have a large number of natural history and scientific works in 
stock, a catalogue of which will be sent on application. 
Mr. W. P. Collins, of 6 Red Lion Square, London, w. c., 
sends us one of his latest catalogues of works on Microscopy and 
Micro-Natural History. Readers, in writing for one of these 
catalogues, should note that Mr. Collins has removed from his Gt. 
Portland St. address. 
CORRESPONDENCE. 
1 The Editor is not responsible forth? opinions expressed by Correspondents .) 
LOCALITIES WANTED. 
Can any reader inform me, where is the most likely place within reasonable 
distance of this part of South London, in which I could make sure of finding 
Helix pomatia, the Roman snail, and also A. galathea , the marbled white 
butterfly ?— Helix, Brixton. 
THE AQUARHJM. 
The “ green slime ” that appears on the glass of Mr. Kemp’s aquarium 
shows that the vessel is placed in a position where it receives too much light. 
Myriads of microscopic spores or germs, are present in all water exposed to 
the air, waiting for suitable conditions under which to develop, and direct sun¬ 
light always leads to their growth and germination. This “green slime,” a 
freshwater alga , is familiar to all who have experimented with aquaria. It may 
be removed by simple rubbing, say with a flannel, but is sure to re-appear if 
the aquarium is not shifted from its well lighted position. I do not think water snails 
are of much use, though they (especially Planorbis corneusxwdiLimncea stagna- 
lis) are constantly busy, rasping away at the growth with their “ lingual rib¬ 
bons ” when kept in affected aquaria. The growth itself will not harm the fish 
or pollute the water, its only undesirable effect being its ultimate opacity. -f.p.p. 
