November 29, 1894] 



NATURE 



1 1 



chance," some brass filings having been dropped accidentally 

 into a pot of molten glass. Afcer the late Dr. Silviati's revival 

 of the glass industry at Murano it was rediscovered, but the 

 present process is a trade secret. The best ^lass is of a copper- 

 brown colour, and transparent to translucent in thin flakes, 

 showing on the edges a pale brown colour. It is filled with 

 innumerable small flakes and spangles of a slightly brownish 

 yellow colour and brilliant metallic lustre, consisting of 

 crystallised copper. Under the microscope the glass shows a 

 porphyritic structure, the ground-mass being composed of a 

 perfectly clear and colourless glass basis. The crystallised 

 portions consist of large phenocryst.«, small phenocrysts, and 

 ..icrolites. The former range in diameter from 0"05 to 0'I2 

 mm., are tubular and extremely thin, the thickness scarcely ex- 

 ceeding o '002 mm., and are perfectly opaque notwithstanding 

 their excessive tenuity. Most of them are hexagonal in outline, 

 the he.xagons being of almost ideal symmetry; but equilateral 

 triangles, which occasionally show truncated angles, also occur. 

 The smaller phenocrysts are much more diverse in crystalline 

 form, and may be generally grouped in one of three divisions : 

 cubo-oclahedral forms, octahedra, and twins. They occur in 

 portions of the glass free from the larger phenocrysts, but filled 

 with abundant microlites, from which they are usually 

 separated by a clear zone. The copper has evidently crystal- 

 lised out from solution in the molten glass exactly like a salt 

 from water, following Lehmann's laws of crystal growth in 

 solutions. Mr. Washington is of the opinion that the glass is 

 produced by melting together glass, cuprous oxide, and some 

 reducing agent, such as siderite ; and that FeO is in this case the 

 reducing agent is shown by the greenish colour of the imperfect 

 glass, which is not the blue green of copper, but the yellow green 

 of ferrous glass, and perhaps due to too large a quantity of 

 reducing agent. 



.\T the last meeting of the French Physical Society, MM. 

 Cailletet and Colardeau read a very interesting paper on the 

 condensation of the gases produced by electrolysis on electrodes 

 formed of metals of the platinum group. It is well known 

 that when acidulated water is electrolysed by means of platinum 

 electrodes that, on removing the battery and connecting the 

 electrodes, a current is obtained in the opposite direction to the 

 original current used to perform the electrolysis. This current, 

 which only last -i for a short time, is explained by the recombin- 

 ation of the hydrogen and oxygen which coat the platinum elec- 

 trodes. The authors, taking advantage of the well-known 

 property of finely-divided platinum of occluding gas in large 

 quantity, were led to use masses of finely-divided platinum con- 

 tained in silk bags as electrodes, and in this way, using electrodes 

 weighing six grms. each, a current was obtained, after discon- 

 necting the battery, which continued for some time, and was of 

 sufficient strength to ring an electric bell. By enclosing this 

 'form of the cell in a receiver, and compressing the air within the 

 receiver, the following results were obtained : — With an 

 additional pressure of one atmosphere, the E.M.F. immediately 

 after charging was i '8 volts, which fell regularly to zero when 

 the cell was discharged. On increasing the pressure the 

 •character of the disch.irge-curve obtained entirely alters, and 

 consists of three parts, (i) A portion in which the intensity 

 of the discharge current rapidly diminishes. (2) A portion dur- 

 ing which the current remains constant. This period occupies 

 the major part of the time occupied in the discharge, and the 

 E.M.F. at this time is about one volt. (3) A second period in 

 which the current diminishes and finally becomes zero. The 

 capacity of such an accumulator, the weight of the two elec- 

 'rodes being I kilogram, is, unier a pressure of 580 atmo- 

 spheres, 56 ampere-hours, while a current of loo amperes can 

 be obtained. To obtain the best possible result, 'he negati' « 

 NO. 1309, VOL. 51] 



electrode should contain three times the weight of platinum in 

 the positive electrode. With finely-divided palladium a storage 

 capacity of 176 ampere-hours per kilogram of palladium was 

 obt.iined at a pressure of 600 atmospheres. It is interesting to 

 note that the storage capacity of an ordinary lead accumulator 

 is about 15 ampere-hours per kilo of metal. 



Leon Guignard, in Ihe Journal de Botanique, adds another 

 important contribution to our knowledge of the centrospheres 

 of plant-nuclei, entitled " Sur I'origine des spheres directrices." 

 It will be remembered that this author was the first to demon- 

 strate the existence of these structures in vegetable cells 

 (Comptes-rendus, 1S91), and also, in a later paper, to describe 

 their behaviour during the origin of the sexual cells and the 

 part they take in the phenomena of fertilisation (./«>;. dis Sc, 

 Nat. 1S91). In these earlier works Guignard already figured 

 many resting nuclei with the centrospheres lying outside the 

 nuclear membrane, and usually in close proximity to it, while 

 within the nuclear membrane are to be seen one or more 

 nucleoli. Strasburger also observed and figured centrospheres 

 outside resting nuclei in Sphacelaria scoparia {Hisl. Biitrii^e, 

 iv. p. 52). Recently, however, G. Karsten was led to believe 

 from a study of the relations of the nucleoli and centrosomes in 

 the mother cells of the spores of Psilottim triquiriim that the 

 centrosomes (or minute bodies included in the centrospheres) 

 owe their origin to the nucleoli, and after karyokinesis are re- 

 included as nucleoli in the daughter nuclei. Guignard's last 

 paper is chiefly concerned with an examination of this point, 

 and he comes to the conclusion that prior to karyokinesis the 

 centrospheres in the cells of the sporangia of P. triquetrum 

 are external to the nuclear membrane, and that after karyo- 

 kinesis, while some of the small nucleoli which have not 

 disappeared during the division of the nucleus are re-included 

 within the nuclear membranes of the daughter nuclei, they 

 remain external to them. 



A RECENT number of the Minnesota Botanical Studies con 

 tains a bibliography on the subject of the fixation of free nitro- 

 gen by plants, embracing over 600 titles. 



The report of the fifth meeting of the .\ustralasian Associ- 

 ation for the Advancement of Science, held at .\delaide, in 

 September 1893, has just reached us from Sydney, where the 

 permanent office of the Association is situated. 



Messrs. Rivington, Percival, and Co. have published a 

 third edition of " Practical Inorganic Chemistry," by Mr E. J. 

 Cox. The book is intended for students preparing for the 

 elementary practical chemistry examination of the Department 

 of Science and Art. 



In the form of " Bulletin No. 56," Mr. P. H. Mell, the 

 State Botanist for Alabama, records the result of a series of 

 observations on the crossing of different varieties of the cotton- 

 plant at the Agricultural Experiment Station at Auburn. 

 The plant is pollinated by the agency of the wind and of in- 

 sects, and he finds inter-crossing to have a material eflfect in 

 increasing the strength of the fibre. 



Miss Ormerod will issue in a few days an abstract of infor. 

 mation on the history and habits of that seriously destructive 

 cattle-pest, the Warble Fly or Ox Bot Fly. The description will 

 be very fully illustrated, and will be an epitome of the knowledge 

 and experience gained up to the present time, and especially 

 during the years 1884 to 1S94. It will deal practically with 

 means of prevention and remedy. The publishers are Messrs. 

 Simpkin, Marshall, Hamilton, Kent, and Co. 



.\N " .-\rtificial Spectrum Top," devised by Mr. C. E Ben- 

 ham, and sold by Messrs. Newton and Co., furnishes an in- 

 teresting phenomenon to students of physiological optics. The 

 top consists of a disc, one half of which is black, while the 



