January 15, 1920] 



NATURE 



515 



extent of the exhibits was also greater, two floors of 

 the physics department of the Imperial College being 

 occupied in place of one, as in previous years, the last 

 being 1913. To some extent this expansion was due 

 to a special reason, namely, the inclusion of a supply 

 of German instruments captured during the war, 

 shown by permission of the Admiralty, the Air 

 Ministry, and the War Office. The attendance was 

 very satisfactory. The fact that the annual Conference 

 of Educational Associations was meeting in London 

 during the week allowed many teachers the oppor- 

 tunity to pay a visit, and we believe this was taken 

 full advantage of. 



There are two sides to an exhibition of this kind, 

 the educational and the commercial, and the two 

 react. The visitor is anxious to buy as well as to 

 learn ; the exhibiting firms are ready to learn as well 

 as to sell. There is much intercourse and interchange 

 of ideas, which may fructify later in the improvement 

 (if old instruments and in the devising of new. 



Although business affairs are by no means stabilised 

 i as yet, the standard reached by the exhibits shows 

 that a keen, progressive, and enterprising spirit is alive 

 amongst makers of scientific appliances. It is not 

 surprising to learn that a great exhibition of products 

 of the British Empire, to be held in London in 192 1, 

 is already in hand. 



Two discourses which attracted good attendances 

 were given daily; one on "The Use of Light in the 

 Transmission and Reproduction of Sound," by Prof. 

 A. O. Rankine ; the second on "Some Polarisation 

 Experiments," by Prof. F. J. Cheshire. In the 

 former was given an exposition of an application of 

 the selenium cell, which suggests the possible super- 

 session of the purely mechanical method of reproduc- 

 tion of speech and music by the gramophone. 



A marked feature of the exhibition was the large 

 number of demonstrations of apparatus in action. 

 There is no doubt that this is widely appreciated, and 

 that the effects in stimulating interest and inquiry 

 are fully commensurate with the pains taken by the 

 firms concerned. Amongst these may be mentioned 

 the production of electrical oscillations by the triode 

 thermionic tube, the indirect compensated illumination 

 known as " Sheringham daylight," and Mr. Darling's 

 simple device for indicating the quenching tempera- 

 ture in the hardening of steel. The model aeroplane 

 cabin with its array of instruments in situ (shown by 

 Hughes and Son) was also most instructive. 



It is impossible in a brief survey to do justice to 

 all the items of apparatus displayed, or to the firms 

 who participated ; only a few can be referred to. 

 First, we would mention thermionic tubes. Few are 

 unaware of the great use that was made of these 

 instruments in the course of the war, and of the many 

 purposes for which they can be employed ; and one 

 -vvas naturally prepared to find, though not less grateful 

 on finding, a fairlv complete exhibition of various 

 stages in the evolution of the diode, and especially of 

 the triode, forms of tube. These were shown by the 

 ' Marconi-Osram Co., the Edison-Swan Co., and H. W. 

 ' lUivan, the production of electrical oscillations by 



.0 of the triode tube being demonstrated. 



The electrical CO. recorder (the Cambridge and 

 Paul Instrument Co.) for the testing of flue-gases 

 furnishes an interesting example of the application of 

 fihvsical principles in combination. The percentage of 

 i irbon dioxide in the flue-gases determines the thermal 



nductivity of the gas ; this determines the rate of 



rjling of an immersed heated platinum wire ; and 



is in turn determines the current in the galvano- 



iKter of an unbalanced Wheatstone bridge, of which 



the platinum wire constitutes one arm. This example 



recalls another instance of the application of indirect 



measurement, namely, the dionic (?) water-tester 



NO. 2620, VOL. 104] 



(Messrs. Evershed and Vignoles), where the electrical 

 conductivity serves to indicate the extent of inorganic 

 impurity present. 



A collection of glasses by Chance Bros., though on 

 a modest scale, was of great interest. It included the 

 Crookes spectacle glasses, which protect the eye by 

 cutting out the ultra-violet rays, and an ultra-violet 

 glass, opaque to the visible spectrum, but transmissive 

 of the ultra-violet. Demonstrations of their properties 

 were made by the aid of a nichrome arc and a 

 fluorescent screen of barium platinocyanide. 



Amongst Hilger's instruments for refined optical 

 measurement we may single out the vacuum spectro- 

 graph (shown bv courtesy of Prof. Fowler), which 

 permits of photographing the spectrum in the 

 Schumann region. 



Optical instruments of high quality were displayed 

 by many firms, including Charles Baker, Hughes and 

 Son, Bellingham and Stanley, Davidson and Co., 

 Watts and Son, W. Ottway and Co., Penrose and Co., 

 Watson and Sons, Newton and Co., and Rheinberg 

 and Co. Exhibits of books by the Cambridge Univer- 

 sity Press, Macmillan and Co., and several other 

 firms were much appreciated. 



There is room, we think, for one criticism of the 

 quality of the exhibits. We refer to the comparative 

 absence of simple forms 'of apparatus. There is a 

 great need, for teaching purposes in schools and col- 

 leges, of apparatus, made without elaboration, of an 

 open type that will proclaim its principle at a glance. 

 Dr. Searle's apparatus occurs to one as a good example 

 of the type desired. Collaboration between teachers 

 and manufacturers would serve to hasten a develop- 

 ment that is urgently required, and we commend this 

 j field to the attention of both. D. O. 



THE CHARTERS TOWERS GOLDFIELD. 



THE Geological Survey of Queensland has pub- 

 lished a very complete description of the Charters 

 Towers goldfield by Mr. J. H. Reid (Publication 

 No. 256). Although this was for' long the most im- 

 portant goldfield in Queensland, and had, in fact, for 

 many years the largest gold output of any of the 

 individual goldfields in the whole of Australia, no full 

 account of the geology of the field or of the nature 

 of the ore deposits has yet been published, so that 

 the issue of the present monograph is fully justified. 

 Furthermore, had the issue of such a work been 

 delayed much longer, it could never have been carried 

 out effectually, as many of the mines are now closing 

 down. The goldfield was discovered in 1871, and ten 

 years later the gold production was close upon 

 75,000 oz. of gold bullion ; in 1887 this output had 

 doubled, reaching 151,500 oz. ; and in 1899 the highest 

 output, namely, 319,572 oz. of fine gold, was attained. 

 From that time the production has been a steadily 

 declining one, the drop since 1912 having been par- 

 ticularly rapid, until in 1916 the output was only 

 33,107 oz. 



Unfortunately, it is only too clear from the report 

 that this falling off is not a temporary phase, but is 

 due to the very nature of the gold deposits themselves, 

 and that the field is rapidly approaching exhaustion. 

 It is shown that the principal country rock is a grano- 

 diorite of Lower Devonian or pre-Devonian age, 

 traversed by numerous dioritic dykes and by well- 

 marked systems of fault-fissures, the throw of the 

 latter being generally inccnsiderable. Within the zones 

 of shattered rock accompanying these fissures veinlets 

 of auriferous quartz have been deposited, undoubtedly, 

 according to the author, by hydro-thermal agencies. 

 The veins are, for the most part, narrow, ranging 

 ns a rule from a few inches to :; ft. in thickness, 



