July 30, 1908] 



h'ATURE 



507 



kept togctlier for sending to great exhibitions in order to 

 testify to the mineral resources of the country ; specimens 

 are added from time to time to replace breakages and to 

 represent newly opened mines. The small specimens are 

 arranged in flat table-cases ; of the large specimens, the 

 more valuable are placed in large upright cases, and the 

 remainder are piled near by in the open court. Informa- 

 tion as to the nature of the ore, and in some instances 

 the minerals present and the locality, is given on the 

 labels accompanying the specimens. We may pass over 

 the gold specimens from British Columbia and the Yukon 

 district, and direct attention to the extensive series of silver 

 associated with smaltite, niccolite, erythrite, &c., from 

 the rich mines of Temiskaming, Ontario, first discovered 

 five years ago. Some large crystals of phlogopite and 

 apatite, and a small polished piece of beautiful blue soda- 

 lite, may be noticed. 



In the Australia Hall the several component States have 

 worked in their own courts independently, and not always 

 on similar lines. In the Western Australia court the 

 organisation and arrangement of the 

 minerals have been managed entirely by 

 the Government, and the result, as re- 

 gards both the type of show-case and the 

 selection and labelling of the specimens, 

 is admirable. The gold industry naturally 

 takes a prominent position. Some rich 

 specimens of tellurides are shown, but 

 ihey reveal no signs of crystal form. At 

 tlie somewhat analogous district of Cripple 

 Creek the telluride of gold, calaverilc, 

 occurs in many-faced crystals, the sym- 

 metry of which has been such a baffling 

 problem. The tantalite from Greenbushes 

 is interesting as the source of the filament 

 of the new electric lamp ; generally it is 

 found in curiously marked massive pieces, 

 but one or two specimens show unmistak- 

 able indications of crystal form. A huge 

 lump, said to be only a portion of the 

 original mass, testifies to the size attain- 

 able by tin-stone. At the principal 

 entrance to the Queensland court an- 

 placed cases containing both rough and 

 cut examples of the gem-stones found in 

 the southern and central districts, viz. 

 opal, colourless topaz, green and yellow 

 sapphire, pink and green tourmaline, and 

 pale green beryl. Conspicuous among 

 them is the novel " black opal," which is 

 of various shades to the deepest blue, 

 and flames with vivid opalescence. Among 

 the ore specimens at the further end of 

 the court may be noted a bright 

 wolframite and a fine bismuth. The gem- 

 stones occurring in New South Wales are 

 verv similar to those just mentioned ; 

 perhaps the best black opal, of which some 

 exceptional specimens are exhibited, comes 

 from Lightning Ridge. Few good speci- 

 mens from the famous Broken Hill mines are to be seen, 

 and the arranging and labelling in at least two of the 

 show-cases leave much to be desired. 



Time, unfortunately, has not permitted of the organising 

 of a collection of typical minerals in the India Hall. The 

 Ruby Mines, Ltd., however, exhibit a magnificent series 

 of rough and cut rubies and sapphires from Burma ; no 

 attempt is made to distinguish between the species 

 corundum and spinel. Those interested in minerals will 

 find much to attract thp:n in the finely-crystallised speci- 

 mens from the new lead and zinc mines at Broken Hill, 

 North-Western Rhodesia, exhibited by Mr. Percy C. 

 Tarbutt in the British Science Hall. They will see the zinc 

 phosphates, hopeite, previously to the discovery of these 

 mines known only by a few rare crystals, and tarbuttite, a 

 new species, which was named after the exhibitor by Mr. 

 L. J. Spencer, who recently described this remarkable 

 mineral occurrence. In the same case Mr. Arthur Russell 

 shows some minerals from the British Isles, mostly from 



Fleischmann exhibits a scries of zeolites from the basaltic 

 lava near Belfast. 



Probably never before has such a superb collection of 

 fashioned gem-stones been brought together for public 

 view as are exhibited in the French and British .Applied 

 Art Halls. Space, however, permits us to direct attention 

 only to the remarkable series of coloured diamonds 

 exhibited by M. Eknayan in the former hall. 



G. F. H. S.- 



PROTECTIVE DEVICES FOR HIGH-TEXSION 



TRANSMISSION CIRCUITS. 

 T N" the Journal of the Institution of Electrical Engineers 

 issued in June (vol. xl.. No. i8g), Mr. J. S. Peck 

 describes some methods in use for protecting high-tension 

 transmission circuits from lightning and other high-voltage 

 discharges. The development of apparatus for this pur- 

 pose has received little attention in Great Britain owing 

 to the fact that there are comparatively few overhead 



abandoned mines or unrecorded localities, and Mr. F. 

 NO. 2022, VOL. 7SI 



N. A. 



systems working at pressures greater than 11,000 volts, 

 and severe thunderstorms are of very rare occurrence. On 

 the Continent and in America, however, where very high 

 voltages are used in overhead systems, and where thunder- 

 storms are more frequent and severe, it has been essential 

 for the success of transmission to develop considerably such 

 protective devices. 



Generallv speaking, the effect of a lightning discharge 

 on the circuit will be to cause a large increase of potential 

 at certain points. Should the line insulation be insufficient, 

 the charge may jump to earth, shattering poles, but 

 probably protecting the apparatus at the end of the line 

 from damage. If there is no escape in this direction, then 

 there is the possibility of the insulation of the end apparatus 

 breaking dow_n, which is very serious. 



Similar dangers may arise from sudden shorts in the 

 system itself, and in dry climates the wind blowing over 

 the transmission wires has been found to build up a high 

 static potential. It is essential, then, to devise apparatus 

 (i) to prevent concentration of potential at the end wind- 



