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SCIENCE-GOSSIP. 



Polynesia xataxs in August. — I see in the 



June issue of Sciexce-Gossip (ante p. 89) that Mr. 

 Fred Enock found some Polynema natans in a 

 pond near Totteridge in May last. It ma}- interest 

 many microscopists to record that whilst dipping 

 in a pond near Shenley, Herts, I found one perfect 

 specimen of this remarkable little aquatic fly late 

 in August, 1895, quite by chance. This seems to 

 point to the species being at least double brooded. 

 — Walter Crosbie, The Chestnuts, Lyonsdoun, New 

 Barnet. 



Questions ox Microscopy. — I think your readers 

 would help to make Sciexce-Gossip more practi- 

 cally useful if they would ask questions concerning 

 technique, etc.. through your columns, and give also 

 the results of any experiments they have made with 

 objects for the microscope. Though some of these 

 may seem trivial to the learned ones, yet I am sure 

 your object is to help the many hundreds of young 

 people who are now taking up the microscope, 

 Their difficulties will be those of many others. I 

 add an instance or two of what I mean. — Adam 

 Clarke Smith, Eastmoor, Bournemouth East. 



[We welcome this communication, and cordially 

 invite others. We have pleasure in announcing 

 that Mr. Martin J. Cole, the well-known profes- 

 sional microscopist, has kindly undertaken to 

 answer questions on technique, and generally assist, 

 through our columns, any students of microscopy. — 

 Ed. Sciexce-Gossip.] 



Marine Glue. — What is the solvent of this 

 cement ? I have been told that wood naphtha is, 

 but 1 cannot succeed. Methylated spirit will — 

 but will not naphtha do ? — A, C. S. 



Mildew in Slides. — I have tried soaking in methy- 

 lated spirit for a few minutes, then brushing the 

 object very softly with a camels '-hair brush. The 

 object must then be thoroughly dried before putting 

 up again. Mildew is a terrible enemy. — A. C. S. 



Marine Glue. — Methylated spirit is the best 

 solvent for marine glue, but why use the latter for 

 microscopical work ? Miller's caoutchouc cement 

 answers all purposes much better. It can be 

 obtained from most opticians ; its solvent is also 

 methylated spirit. — M. J. C. 



Mildew in Slides. — The remedy you have applied 

 is all you can do. The cause of the mildew is 

 either that the specimen was not quite dry before 

 mounting, or that the cell was not properly sealed 

 up. Dry mounts should always have two or three 

 coats of some good shellac cement, such as Miller's 

 caoutchouc. — M. J. C. 



What Becomes of Hydras. — The Rev. G. C. 

 Bateman, in his interesting book on the Aquarium, 

 page 301, says that " they apparently disappear in 

 the autumn." At page 254 of Kerner and Oliver's 

 '• Physiology of Plants," it is stated that Hydra is 

 ,; an instance of symbiosis," the alga in partner- 

 ship with it being furnished with chlorophyl. 

 About six weeks ago I had a very fine Hydra lividis, 



which, under a good food supply, was budding 

 freely. I had to go away from home for a fort- 

 night, and left it in a glass plentifully supplied 

 with entomostraca, expecting to find it on my 

 return a rival to the giant one figured in the last 

 edition of " Carpenter on the Microscope." It 

 had, however, vanished out of sight, and the ento- 

 mostraca were flourishing. Had the}- eaten it ? A 

 few days since I had another Hydra vividis in a cell 

 slide in a very active state, till one day I gave it 

 a drop of water that had some mycelia in it, when 

 that Hydra, too, disappeared, and left nothing 

 behind it, unless it may have been a trace of the 

 symbiotic green algae which had flourished on it. 

 I could find no vestige of this Hydra under the 

 microscope. Can any of your correspondents 

 explain this ? Does Hydra fusca turn into Hydra 

 vividis by means of green alga spores settling on 

 it ? The former is found here in clear water on 

 willow-roots, which are of its colour ; the latter is 

 on Lemna in ponds. Is the symbiotic theory 

 correct ? — Wm. N. Varrand, Maj.-Gen. R.E., 

 Westhorpe, Southwell; December 10th, 1895. 



High Magxificatiox. — There is a prevailing 

 idea in the minds of many amateur microscopists, 

 notwithstanding the repeated efforts that have 

 been made to eradicate it, that enormous magnifi- 

 cation is the essential for the examination of 

 minute structure. There was a time when 2 ij-inch, 

 rr'j-inch, and even objectives of still higher power, 

 were considered desirable additions to the equip- 

 ment of the microscopist. Before the relation of 

 aperture to power was understood, it was possible 

 for such objectives to have been thought advan- 

 tageous, but examined from the standpoint of 

 modern optics, they have no raison d'etre. It is 

 therefore a matter for surprise to find in the " Pro- 

 ceedings " of the American Microscopical Society 

 the following paragraph: — "Dr. Ephraim Cutter, 

 of New York City, then gave a vivid description 

 of a Jg-inch objective, whose performance he con- 

 sidered a triumph for America, and a great credit 

 to Mr. Tolles, by whom it was made." The 

 claims of this -J^-inch have been further energeti- 

 cally pushed in an American journal devoted to 

 microscopy. Its marvellous performances, from 

 the owner's point of view, the difficulties en- 

 countered in the manufacture, the enormous cost 

 (roughly, /So), and the people who have looked 

 through it with wondering eyes, have all been 

 minutely described. It may be, and probably is, 

 a curiosity, and a marvel of the optician's skill. 

 but a modern oil immersion jVinch lens, costing 

 £5, correctly used, would reveal far more fine 

 detail than this much-lauded Jg-inch. 



There are many microscopists yet to be met 

 with, who, if thev were offered a choice between a 

 dry g'g-inch or higher power, and an oil-immer- 

 sion ^-inch of large aperture, both by equally 

 good makers, would unhesitatingly select the 

 former, because of its imagined effectiveness in 

 consequence of the greater magnifying power that 

 it would yield. This ignorance is not confined to 

 "unattached" microscopists, that is, such as are 

 not members of clubs or who live away from 

 centres of microscopical work, for it was but three 

 or four months ago that a gentleman was exhibiting 

 a diatom, with a dry lens of high power, in the 

 meeting room of a Microscopical Society at Hanover 

 Square, and was claiming for it an equality with, 

 if not a superiority to, oil-immersion lenses. 



Before proceeding further, it must be clearly 

 stated and understood that it is the aperture of an 



