HARD WICKE 'S SCIENCE - G OS SI P. 



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London, and the committee cordially invite the co- 

 operation of all entomologists, especially those who 

 are willing to further the objects of the society by 

 reading papers and exhibiting their captures. Since 

 its fonnation the society has rapidly increased in 

 numbers, a large portion of the members being ex- 

 perienced collectors. Subscription, 6s. per annum, 

 with an entrance-fee of is. Hon. Secretaries — Mr. G. 

 C. Champion, Mr. W. C. Chancy. 



Greetihithe Naturalists' Society (founded 1872). — 

 President, Rev. J. M. Gatrill ; Secretary, S. Martin. 



East London Natural History and Microscopical 

 Society (founded 187 1 ). President, J. M. Knight, 

 Esq. — Meetings held fortnightly on first and third 

 Thursdays in each month, at the Board School, 

 High-street, Bromley. Gentlemen desirous of join- 

 ing the society can obtain further information from 

 the Hon. Secretary, Mr. Harry Smart, 8, The Para- 

 gon, Hackney, E. 



Toivei--liill Microscopical Club (established July, 

 1872). — Its meetings are held on the second Tuesday 

 in each month, with excursions on Saturdays in the 

 summer months. The Soiree held in February. 

 President, Mr. James B. Crosfield; Hon. Secretary, 

 Mr. R. Sedgwick. 



The Charterhouse Science and Art Society (founded 

 October, 1875). — It has for its object the reading and 

 publication of papers connected with the numerous 

 subjects embraced by science and art, and the collec- 

 tion of objects for a museum which has been esta- 

 blished in the school. President, Rev. G. S Davies, 

 M.A.; Secretary, S. D. Titmas, B.Sc, F.C.S. 



Greenwich Microscopical and N'atural History 

 Society. President, Prior Purvis, M.D., London; 

 Hon. Secretary, Geo. Dannatt. — Meets on the first 

 and third Thursdays in each month. Annual sub- 

 scription, los. Each member supplied gratis with a 

 monthly copy of Hardwicke's Science-Gossip, 

 and entitled to two tickets to the Annual Soiree. 

 The last Soiree was held in the Lecture Hall, Green- 

 wich, on February 14th. 



[We shall be glad to hear further from the honorary 

 secretaries of other London societies, inasmuch as 

 we hold it to be of importance that the existence of 

 such clubs should be widely known.] 



MICROSCOPY. 



Securing Cover-glasses. — Your correspondent 

 "A.S.G.," in the January number of Science- 

 Gossip, asks for some plan of securing the cover- 

 glass over dry objects, so that the water used with 

 immersion-lenses will not run in and spoil his tests. 

 Perhaps a plan I have for years adopted may meet 

 his wishes, and, therefore, I ask you to find room for 

 this small communication. The method I advocate 

 consists in filling in the angle between the edges of 



the covering-glass and the slide with a compound of 

 wax and Canada balsam, which can be easily done 

 by melting this mixture, and dipping a heated piece 

 of wire into it, and then running it round the edge 

 of the cover, and so sealing it up that any cement 

 put on afterwards cannot run in : the wax composi- 

 tion sets directly it touches the cold slide. This plan 

 may also be adopted in mounting any opaque object 

 in a deep cell, allowing the removal of tlie cover 

 should a dewiness at any time become apparent on its 

 inner surface ; it is also a useful thing sometimes to 

 employ this composition for the rapid construction of 

 temporary troughs for the examination of microscopic 

 life, and I hope the knowledge of this may meet the 

 want of "A. S. G.," as well as the many microscopic 

 readers of your journal. — T: Chatiers White. 



Heliofelta Metii.— The separation of the 

 frustule into two valves, with the number of rays 

 differing, is not unusual. I have often found this to 

 be the case, not only in this genus (if it be really 

 distinct), but in Actinoptychus the valves themselves 

 often separate into dissimilar plates (and which I 

 designate secondary plates, and called by Schmidt in 

 his Atlas, regeneration-valves) ; this secondary plate 

 in Heliopelta and Actinoptychus is usually marked 

 with fine decussating punctate, appearing under a low 

 power like watered silk, or moire antique. The only 

 exception to this, so far as I am aware, is in A. undu- 

 tatus. The secondary plate in this species is faintly 

 but coarsely punctate, the punctje connected with 

 each other by fine lines ; the surface is scarcely 

 undulate, and not divided into compartments like the 

 primary plates. Frustules of Aulacodisca also fre- 

 quently have valves in which the nodules differ in 

 number. I have separated frustules of A. viargari- 

 taceits, one of the valves having only four, whilst the 

 other had six ; and some double frustules have had 

 different numbers on all four valves ; this is, however, 

 not peculiar to that species. I have detected it in the 

 following : — A. Kittoni, A. Kittoni, var. Africamts, 

 A. Oreganus, zxidi A. pulcher. The same thing occurs 

 in Eupodisc2is Argus and E. Rogersii. As entire frus- 

 tules do not mount well, excepting in front view, the 

 following hint for separating the valves may be useful. 

 Push the specimen away from the other diatoms, and 

 let it dry (taking care, however, that it does not skip 

 away, which it is very apt to do if the valve is upper- 

 most : I always keep the trestle upon it until it is 

 perfectly dry) ; then transfer it to a drop of water 

 on a clean slide. The expansion of the air inside 

 frequently splits the frustules ; if it does not, heat it 

 quickly over the lamp, and success is almost certain. 

 Before the drop dries up, add another, and examine : 

 manipulation with the breath will thoroughly detach 

 them, and also separate the primary and secondary 

 plates.- — F. Kitton. 



Crystal Prisms of Allium Porrum.— The 



