June 26, 1913] 



NATURE 



433 



tioned the introduction of the Palmyra palm, so that 

 the production of sugar by this and the date palm 

 would extend over the whole year. In this way the 

 erection of large central factories might be rendered 

 possible. Consideration of the amounts of sugar 

 obtainable from various sugar-yielding plants shows 

 that greater quantities are to be expected from the 

 date palm than from sugar cane in this district, and 

 that the average yield of the former per tree is about 

 seven times that of the sugar maple. Greater output 

 of sugar and greater purity of product would also 

 accrue from the disinfection of the tapped surface 

 and of the collecting vessels by means of formalin. 



The whole of vol. xxii., part i., of the Memoirs of 

 the Indian Meteorological Department is devoted to 

 tables containing monthly and annual rainfall normals 

 at all stations maintained by the Imperial and pro- 

 vincial Governments where records for at least five 

 years are available. There is no discussion attached 

 to this very valuable mass of materials, but the 

 number of years over which the data extend has 

 been given for each station, in order that an estimate 

 may be formed of the trustworthiness of the results. 

 As might be expected from other publications of the 

 department, some of the figures are very remarkable. 

 Among the average annual amounts may be men- 

 tioned : — Cherrapunji (Assam), 426 in. ; Malkompeth 

 (Satara, Bombay), 274-8 in. ; Launglon (Burma), 

 234-3 ' n - ! Rujanpur (Punjab), 3-7 in. ; Rohri (Sukkur, 

 Bombay), 3-1 in. ; Jhatput (Baluchistan), 30 in. At 

 "stations outside the Indian land area" still smaller 

 values are quoted : 27 in. at Aden, 2-5 in. at Bahrein 

 (Persia) and at Perim (Asiatic Turkey). 



The October, 1912, number of the Sitzangsberichte 

 of the Vienna Academy of Sciences contains a short 

 paper by Dr. W. Altberg, of Odessa, on the use of 

 the resistance offered by a small sphere to the passage 

 of a current of gas past it as a measure of the velocity 

 of the gas. He used a steel sphere o-6 cm. diameter, 

 suspended by a metal filament 0-0025 cm. diameter, 

 75 cm. long, in the centre of an air duct through 

 which a stream of air of known velocity could be 

 passed. The deflection of the suspension from the 

 vertical was measured by means of a microscope 

 reading to 0001 cm. The author finds that the 

 arrangement is easily set up, adjusts itself almost 

 instantaneously to changes of velocity, and allows 

 velocities from 70 to 270 cm. per second to be deter- 

 mined with accuracy by means of the relation shown 

 by Becker to hold for lower velocities, i.e. the resist- 

 ance offered by the sphere is the sum of two terms, 

 the first representing Stokes's law — resistance propor- 

 tional to the radius of the sphere, the velocity and 

 viscosity of the medium — the second representing 

 Newton's law — resistance proportional to the square of 

 the radius, the density and the square of the velocity 

 of the medium. 



The Verhandlungen of the German Physical Society 

 for April 30 contain a preliminary account of the 

 measurements made by Dr. R. Reiger, of the Univer- 

 sity of Erlangen, on the effect of introducing explor- 

 ing electrodes of various kinds into thei positive 

 column of the discharge through a vacuum tube. 

 NO. 2278, VOL. 91] 



The change in appearance of the discharge was 

 studied by photography, and the effect on the total 

 fall of potential down the tube was measured. As a 

 result the following conclusions are drawn : — In the 

 immediate neighbourhood of the exploring electrode 

 free electric charges are produced, and the total fall 

 of potential is increased by an amount which in- 

 creases with the diameter of the electrode and with 

 the gas pressure in the tube. The material of the 

 electrode and whether it is covered with glass or not 

 make little difference for small electrodes, but for 

 those of large diameter metals produce greater dis- 

 turbances than insulators. On both anode and 

 kathode sides of the electrode there are large falls 

 of potential, .that on the anode side being the greater. 

 This produces serious errors when observations with 

 double electrodes near together are made. In all 

 cases it is advisable to use as thin exploring electrodes 

 as possible. 



We have received an illustrated pamphlet of seventy 

 pages, by Herr Walther Dix (" Das selbstgefertigte 

 Lichtbild," Quelle and Meyer, Leipzig, price 1 mark), 

 which seems to indicate that even in Germany it is 

 desirable to urge the advantages of photography and 

 its applications in connection with the teaching and 

 the study of chemistry and physics. The author 

 divides his subject into sections, and gives examples 

 of the various uses of photography, after referring 

 shortly to methods of making lantern-slides and paper 

 prints. He says that photographs can well illustrate 

 the details of various pieces or series of apparatus 

 and the methods of using them ; the methods of 

 experimental work ; the arrangement of important 

 technical installations, if possible, by way of prepara- 

 tion for a visit to the works ; the latest progress in 

 connection with recent discoveries that the student 

 deals with in his course of study ; and the graphic 

 representation of various matters, as by curves, which, 

 by showing clearly the points to be demonstrated, 

 will make them more easily remembered. The 

 examples given are taken from many different sources 

 and well illustrated. 



A remarkable advance in the preparation of "con- 

 ductivity water " is described by Mr. R. Bourdillon 

 in the Transactions of the Chemical Society. In the 

 case of one sample of water, which was stored in a 

 vacuous vessel during five years in contact with 

 platinum electrodes, the conductivity was reduced by 

 Kohlrausch some years ago to 0-04 gemmho ; but when 

 the water is to be used in contact with air it has been 

 regarded as a high standard to attain to a conductivity 

 as low as 1 gemmho in ordinary laboratory practice. 

 The production by Bousfield of unlimited quantities 

 of "gemmho water" by continuous fractional dis- 

 tillation of tap-water satisfied this requirement admir- 

 ably. A further substantial improvement was subse- 

 quently effected by fractionally distilling the product 

 under reduced pressure. In Mr. Bourdillon's appa- 

 ratus the fractionation is intermittent and not con- 

 tinuous, but by passing purified air through the steam 

 as it condenses a large middle-fraction amounting to 

 6 or 7 litres can be collected with a conductivity of 

 the order of o-i gemmho. Such highly purified water 



