113 



HAllDWICKE'S SCIENCE. GOSSIP 



[June 1, 1867. 



Dust on Aquaria. — 'Would it not be better to 

 prevent the dust getting into an aquarium than 

 adopting any of the ingenious (?) plans which some 

 of your correspondents have suggested to get rid of 

 it after it has got there ? The way I do it is by 

 keeping one, two, or more pieces of glass (according 

 to the size of the vessel) on the top of the tank, 

 which not only effectually keep out dust, but also 

 prevent any loss of water by evaporation, and the 

 escape of any of the live-stock. — Geo. Abbott. 



Double Oranges. — Oranges such as are men- 

 tioned by your correspondent H. H. (p. 118) are 

 not of unfrequent occurrence, and originate in all 

 probability from the formation of a second row of 

 camels within and above the first. In those 

 instances where the latter do not completely close 

 over the supernumerary organs, but leave them 

 more or less exposed, the nature of the case is 

 obvious. H. H. will find references to similar fruits 

 in ''Trans. Linn. Soc," vol. xxiii. p. 366, and 

 specially in a paper of M. Clos in the fifth scries of 

 the "Annales des Sciences Naturelles," t. iii., 

 p. 312— 31. T. 31. 



Book Wanted. — I should be very glad if any 

 reader of Science-Gossip could inform me where 

 I could meet with a copy of Witham's " On the 

 Internal Structure of Fossil Vegetables of the Car- 

 boniferous and Oolitic Periods." I believe the 

 work is out of print, but some of the readers of the 

 Gossir may know of a second-hand copy. — John 

 Bzdtericorth. 



Gnat Pites. — As there is the probability of a 

 large supply of gnats this summer, can you or any 

 of your readers furnish a remedy for their very 

 troublesome, and to me very painful bites ? — D. G. 



Eako apopiiyllite. — Your correspondent A. S. 

 (in Science-Gossip of May, 1867,) will perhaps 

 find the following information sufficient. The 

 mineral known as Apopiiyllite ichthyophthalmite 

 albine belongs to the zoolitic series, but differs from 

 other zoolites in its chemical constitution, the silicate 

 of lime taking the place of the silicate of alumina. 

 It consists chemically of a double silicate of potash, 

 with eight equivalents of silicate of lime, and six- 

 teen equivalents of water. Its specific gravity is 2'3 

 to 2'16; the degree of hardness, -±'5 to 5 (the diamond 

 being 10). Acids easily decompose it, and it fuses 

 readily with the blowpipe, colouring the flame a yel- 

 low-red, and gives off water. It crystallizes in right 

 square prisms, generally Avith truncation of the 

 angles, or quadrate pyramids, and more rarely in 

 quadrate tables with truncate angles or foliated 

 masses. In colour it varies from a vitreous trans- 

 parency to rose-red and brown. Apopiiyllite is 

 found at Andreasberg, in the Ilarz Mountains, of 

 a rose colour ; in the Earoe Isles colourless. The 

 tabular form, or ichthyophthalmite (fishes'-eyes 

 stone) is found in the Eassathal, South Tyrol. A 

 variety of Apopiiyllite called tesselite or tesselated 

 Apopiiyllite, when cut in thin plates transversely 

 to the axis, appears when polarized to consist of 

 nine crystals, contained within a number of parallel 

 veins or plates. The central crystal has only one 

 axis, and no double refraction, the other two. (See 

 " Pereira on Polarized Light.") — F. Kitton,Noricich. 



The Value or Scientific Knowledge. — The 

 late Edward Eorbes was in the habit of relating an 

 excellent anecdote illustrating the practical advan- 

 tages which the public sometimes derive from the 



delivery of public lectures on natural history. In 

 one of his popular discourses on jelly-fishes, de- 

 livered in a small town in Scotland, he had been 

 demonstrating to the audience how very few grains 

 of solid matter a cartload of medusae would con- 

 tain, and how useless it would be to distribute these 

 animals over the land as manure. At the close of 

 the discourse, a canny farmer stepped up to the 

 j platform and tendered his thanks for the hint, for 

 at considerable expense he had been in the constant 

 habit of collecting and distributing myriads of these 

 creatures, under the impression that his crops would 

 be improved by their presence. —Dr. Cobbold's 

 " New Entozoic Malady." 



Exchange of Slides. — The Quekett Microsco- 

 pical Club has just issued the following rules for 

 the exchange of slides : — 



I. That all slides be deposited with the Ex- 

 change Committee. 

 II. That the slides be classified by the Committee 

 into sections, numbered according to 

 quality. The first section to be a special 

 class for rare specimens, the value of which 

 will be determined by the Exchange Com- 

 mittee. 



III. Members to select from the class in which 



their slides are placed, after the ordinary 

 meetings of the club. 



IV. Members may leave the selection to the Ex- 



change Committee, if they prefer it. 

 V. Slides once exchanged cannot be exchanged 

 again. 

 VI. A register shall be kept in which the slides 

 deposited shall be entered and numbered, 

 witli the date of receipt, and in which 

 exchanges shall also be noted. 

 VII. All expenses incurred in the transmission of 

 slides, or in correspondence respecting 

 them, to be borne by the member on whose 

 account such charges may be incurred. 



Parcels to be addressed — 



Note. — As much inconvenience frequently arises 

 from the breakage of slides in transmission through 

 the post, the following method is recommended : — 

 Pack the slides in a small wooden box, which can 

 be obtained of any optician, tie it securely with 

 string, and attach a slip of parchment to one end, 

 sufficiently large to receive the postage stamps, 

 address, and local Post-office stamps during trans- 

 mission. If paper be used as a wrapper to the box, 

 the colour should be black. When twelve or more 

 slides are sent, they should be packed in a racked 

 box, and forwarded by railway carriage prepaid. 



Black Surface.— What is the nature of the 

 solution ordinarily in use by opticians to give a 

 dead black surface ? Lamp-blaclc mixed with shell- 

 lac dissolved in alcohol would give a glossy black. 



