October i6, 1919] 



NATURE 



137 



man might be rendered possible, but at present his 

 relation to the African West Coast "can be only one 

 of tolerance." 



The manganese ores of the Shimoga and adjacent 

 districts are interestingly described by Mr. B. Jayaram, 

 Senior Geologist to the Department of Mines and 

 Geology of Mysore (Records, vol. xvi., part 2, 1917). 

 The author suggests that percolating waters have 

 brought the manganese, and the iron with which it is 

 always associated, from the silicates of the basic 

 chloritic schist scries, and have deposited the ores as 

 a replacement of the limestones and grits in which 

 they are now found. The rocks termed limestone and 

 grit' are not true sediments, but secondary products 

 •of an igneous complex. 



Attention was directed to the magnesite deposits 

 of Canada in Nature, vol. c, p. 490, 1918. Those 

 of Bulong, north-east Coolgardie goldfield, are now 

 described bv the Geological Survey of Western Aus- 

 tralia (Bulletin 82, igig). The magnesite, which is 

 in numerous veins a few inches wide, has arisen from 

 the decomposition of a great band of serpentine, and 

 it is suggested that augite as well as olivine has sup- 

 plied the magnesium required for its formation. The 

 silica set free is probably responsible for the capping 

 of "siliceous laterite, usually opaline in composition," 

 which is stated to occur in the magnesite areas. The 

 value of the magnesite is estimated at \l. per ton en 

 the ground, the export value being nearly 4!. per ton. 

 One of the means by which supplies of potassium 

 compounds were eked out during the war period was 

 the recovery of potassium salts from the flue-dust 

 which occurs as a waste product in the manufacture 

 of Portland cement. The principal methods employed 

 depended upon treatment of the flue-gases by water- 

 spravs or by a process of electrical precipitation. An 

 account of the various installations devised for the 

 purpose has been published by the Department of 

 Mines, Ottawa (Bulletin No. 29, "Potash Recovery 

 at Cement Plants "). It contains descriptions of the 

 recoverv systems developed at a number of cement 

 factories vn the United States, together with an his- 

 torical review of the whole question and full references 

 to the literature of the subject. 



Attention may be directed to a useful series of 

 articles on the mechanical handling of chemical 

 materials, by Mr. G. F. Zimmer, which have recently 

 appeared in the Chemial Age (Nos. 10 to 15). It has 

 been remarked that chemical works in this country are 

 rather poorly equipped with labour-saving machinery. 

 In present circumstances, when the cost of manual 

 labour has increased so greatly, it may be necessary 

 to pay more attention than formerly to devices which 

 will reduce this cost. The articles in question will 

 help to show how this may be done. They are illus- 

 trated, and well worth consulting by chemists in 

 charge of factories. 



Messrs. Lumi^re and Seyewetz have published in 

 the British Journal of Diotography (October 3, Colour 

 Supplement) a simplified method for the development 

 of autochrome plates. The developer is prepared of 

 two degrees of concentration, so arranged that if the 

 weaker is applied first to the plate, the time that is 

 taken in producing the first outlines of the image 

 (neglecting the sky) will be exactly the time that the 

 stronger solution will require to complete develop- 

 ment. -Although a watch or clock may be used for 

 the timing, a simple sand-glass has many advantages. 

 The sand is started running when the weaker solu- 

 tion is applied, then on the first appearance of the 

 image the glass is put on its side ; the weaker solution 

 is poured off and the stronger poured on, and the 

 sand-glass put upright. When the sand has flowed 

 NO. 2607, VOL. 104] 



back again the development is complete. In the 

 formula given the concentrations of the developers are 

 as I to 10. 



Sir Charles Bright read a paper on "Inter- 

 Imperial Communication, through Cable, Wireless, 

 and Air Methods," before the Section of Economic 

 Science and Statistics at the Bournemouth meeting 

 of the British Association. He pointed out that it is 

 conceivable that national and imperial interests can 

 be adequately provided only by the_ State controlling 

 at least one complete cable to all points of the British 

 Empire, supplemented by an all-British wireless 

 chain. The recently established Telegraph Communi- 

 cations Board, first urged by the author seventeen 

 years ago, is intended for generally controlling and 

 developing inter-imjjerial telegraphic and aerial corn- 

 munication in national and public interests. By this 

 scheme all the Government departments concerned 

 (strategic as well as civil) are represented by 

 delegates, who meet periodically to discuss and 

 settle all matters germane to the subject. This 

 should do much towards improving the previously 

 existing arrangements by which the Post Office alone 

 represented the Government. Besides increased cable 

 and wireless facilities being necessary and the war 

 devastations made good, it is highly desirable that 

 improved methods of message condensation should be 

 introduced so as to get the best results from existing 

 facilities. The field open to inter-imperial air corn- 

 munication is considerable ; air organisation and air 

 routes are amongst the important questions of the day, 

 and it is suggested that all aerial mail communications 

 should be rationed. 



An important paper on the theory and use of radio- 

 direction-finding apparatus by Capt. A. S. Blatterman, 

 of the U.S. Army, appears in the Journal of the 

 Franklin Institute for September. It is known that 

 in radio stations it is sometimes possible to hear 

 signals when the antenna is disconnected from the 

 apparatus. Hence the passing waves induce sufficient 

 electromotive forces in the coils of the receiver to 

 produce audible signals. .An investigation was there, 

 fore carried out in the U.S. radio laboratories in 1917 

 and 1918 to find out the most efficient shape of coil 

 to receive signals directly. As the loudness of the 

 signals varies with the position of the coil, an inves- 

 tigation was also made of the most efficient shape of 

 coil for direction-finding. Elementarv theory would 

 lead us to suppose that the coil would be more effec- 

 tive the larger its cross-section and the greater its 

 time-constant. It would also appear that the loudness 

 of the signals is inversely proportional to the square 

 of the wave-length. This, however, is not the case. 

 The experiments recorded in this paper prove that 

 there is a certain size of coil which gives the best 

 results for a given wave-length. This was traced to 

 the fact that the resistance of the coil varies with the 

 wave-length. For very long wave-lengths the resist- 

 ance has its ordinary value. .As the wave-length is 

 shortened, and therefore as the frequency is increased, 

 the resistance increases slowlv until it is two or three 

 times its ordinary value, and it then increases with 

 great rapidity. This effect makes the reception bad at 

 high frequencies. There is, therefore, a certain sized 

 coil which produces the best effects. The results of 

 the experiments described prove this conclusively. A 

 thorough investigation is also given of the directional 

 characteristics of this tvpe of receiver, and many 

 curious properties depending on its height above the 

 ground were discovered. Using a properly constructed 

 coil in an ordinary room and a seven-stage amplifier, 

 the signals issued by all the high-power European 

 stations could easilv be heard. 



