September 12, 1907] 



NATURE 



501 



to the counties of Gloucestershire and Worcestershire 

 compelling growers to take measures against the goose- 

 berry mildew disease. 



In the Agricultural News (July 27) particulars are given 

 regarding the efforts that are being made to establish an 

 industry in Sea Island cotton in Tobago ; with this object 

 in view seed has been distributed, and a ginnery is in 

 course of erection at Scarborough. In connection with 

 the disinfection of cotton seed with corrosive sublimate 

 in wooden vessels, experiments have shown that the 

 mercury salt is absorbed, so that it is recommended to 

 give the vessels a preliminary soaking before disinfecting 

 the seed with a fresh solution. A note on the exhibition 

 of limes from Dominica records the award of a gold medal 

 at a recent show of the Royal Horticultural Society. 



The Engineering Standards Committee has issued the 

 British standard specification for steel castings for marine 

 purposes (No. 30, price 25. 6A net). The present specifi- 

 cations of the .Vdmiralty, the Board of Trade, and the 

 three leading registry societies were carefully compared, 

 and from these the specification has been prepared. 



A SPECIAL number of the Far Eastern Review (vol. iv., 

 No. i) has been published devoted to the mining indus- 

 tries of the Philippine Islands. The important part played 

 by the mineral industry in the American development of 

 the Philippines is clearly shown. In at least one district 

 gold has been taken out in payable quantities, and the 

 development of the coal deposits is making satisfactory 

 progress. 



A LENGTHY paper on the origin of the gold in the 

 Witwatersrand banket, by Prof. J. W. Gregory, is pub- 

 lished in the Bulletin of the Institution of Mining and 

 Metallurgy (No. 35). He considers that the theory in best 

 agreement with the facts appears to be that which re- 

 gards the banket as a marine placer in which gold and 

 black sand (magnetite with some titaniferous iron) were 

 laid down in a series of shore deposits. The gold was 

 in minute particles, and it was concentrated by the wash 

 to and fro of the tide, sweeping away the light sand and 

 silt, while the gold collected in the sheltered places 

 between the larger pebbles. The black sand deposited 

 with the gold has been converted into pyrites, and at the 

 same time the gold was dissolved and re-deposited in situ. 

 The absence of conclusive evidence of any considerable 

 impoverishment in depth is an argument in favour of the 

 alluvial origin of the gold, and is favourable to the further 

 extension of the banket in depth. 



The facilities provided by liquid air are leading to a 

 rapid extension of our knowledge of the properties of 

 substances at low temperatures. Mr. H. G. Dorsey, of 

 Cornell University, is at present engaged in investigating 

 the coefficients of expansion of solids, and gives in the 

 August number of the Physical Review an account of the 

 results obtained for quartz glass, ordinary glass, and 

 several pure metals and alloys. For quartz glass the 

 coefficient is negative below and positive above 190° 

 absolute, remaining very small throughout, while for all 

 the other substances tested it is positive, and increases 

 with rise of temperature. In the case of gold, the curve 

 connecting temperature and coefficient is undulating. The 

 method used by Mr. Dorsey is a modification of Fizeau's, 

 the interference taking place between rays reflected at 

 the top surface of a sheet of black glass, on which a 

 hollow cylinder of the material to be tested stands, and 

 those reflected from the under surface of a sheet of clear 

 NO 1976, VOL. 76] 



glass supported on the cylinder. Temperature corrections 

 are obviated by placing the apparatus in an exhausted 

 chamber. 



The merits of aluminium conductors are likely to be 

 freely discussed, owing to the fact that insulated 

 aluminium cables have recently been placed on the market 

 by one of the well-known cable companies. Bare 

 aluminium conductors have been used already in this coun- 

 try and largely used in America, but insulated aluminium 

 cables have up to the present been practically unknown. 

 The difficulty of making sound joints has been the trouble 

 which has prevented a larger use of aluminium for com- 

 mercial purposes, but this difficulty, it is stated, has been 

 overcome, and both mechanical and " sweated " joints 

 can be made as desired, and the makers claim that the 

 electrical and mechanical properties of the joints are 

 superior to those of the wire itself. Owing to the con- 

 ductivity of aluminium being only 60 per cent, that of 

 copper, the diameter of the cable carrying the same 

 current is, of course, greater. How this will affect the 

 cost when insulated aluminium conductors are employed 

 still remains to be seen, as no figures are given as yet 

 as to the price as compared with insulated copper cables. 

 A 50 per cent, saving in weight is claimed over copper 

 conductors of the same capacity, with an increase in 

 diameter of 28 per cent. The insulation used is vulcanised 

 bitumen, as being lighter than paper, for the same degree 

 of insulation. Doubtless practical experiments in the use 

 of these cables will now be made, since the jointing difficul- 

 ties have been overcome, and the commercial utility of 

 insulated aluminium cables will be tested. 



The Electrician for August 30 contains a note on a new 

 system of wireless telephony described by the inventor. 

 Prof. Majorana, at a recent meeting of the Associazione 

 Elettrotecnia Italiana, which is based on the use of a 

 spark gap. For generating the spark a special rotating 

 arrangement is used, and it is claimed that 10,000 single 

 sparks per second can be obtained. These conditions 

 entailed a special microphone, and the Majorana hydraulic 

 microphone, which depends on the capillary action of fluid 

 jets, answers this purpose. With this microphone Prof. 

 Majorana has obtained telephonic currents of very great 

 clearness and strength. The microphone consists of the 

 usual mouthpiece and of a membrane fixed to a glass tube 

 which moves freely under the oscillations of the mem- 

 brane, and through which slightly acidulated \vater flows. 

 A special opening in the tube allows the liquid to pass 

 out and strike the upper surface of two cylindrical pieces 

 of platinum which are insulated from each other. This 

 is called the "collector." On striking the middle of the 

 " collector " the fluid spreads over the surface, making 

 contact permanently between the two halves. If a battery 

 is connected in circuit with a telephone and the 

 "collector," so long as the membrane is not disturbed 

 by sound waves, a constant current will flow. As soon, 

 however, as the membrane vibrates the aperture oscillates 

 and varies the flow of drops, so that the thickness of the 

 fluid on the collector is always altering. Prof. Majorana 

 conducted his experiments with a spark gap, and got 

 some satisfactory results, but at the same time he found 

 that by using the Poulsen arc in nitrogen certain 

 advantages accrued. 



The report of the Meteorological Committee for the 

 year ended March 31, 1907, recently presented to Parlia- 

 ment, records great activity in all branches of the useful 

 work of the office, and is more than usually interesting 

 from various points of view. Both the daily and w'eekly 



