470 



NATURE 



[March 14, 1895 



those of its scams into which electrical hauling-engines had 

 been introduced to drive endless ropes, and to replace horse- 

 traction between the main haulage -roads and the working-faces. 

 The electrical generating plant comprised a dynamo for supply- 

 ing power to the electrical hauling-engines, capable, at a speed 

 of 620 revolutions per minute, of an output of loo amperes at 

 490 volts. Two electrical hauling-engines, of which the main 

 features were similar, were used. The two cables of s'randed 

 steel wire \ inch in diameter, operated circuits of 2l6o yards 

 and 1020 yards in length respectively. The cables were driven 

 continuously at a uniform speed, and the coal-hitches were 

 attached to or detached from them by a Smallman clip. The 

 efficiency of the plant as compared with the horse- traction, 

 which it had replaced, was also considered. The electrical 

 haulage-system in the Ell coal seam was capable of a daily out- 

 put of 400 tons. The daily output by horse-traction had been 

 180 tons, and to increase this to 403 tons, thirty or forty horses 

 would have been required, a number which could not have been 

 employed in the available space wiihout confusion. The daily 

 output of the electrical haulage-system in the main coal-seam, 

 which was not yet working at its full capacity, was between 

 150 and 200 tons. The yearly working expenses of the two 

 systems were compared, upon the results of one and a half 

 years' working, and were found to be ^4130 and ^^1990 by 

 borse-traction and by elec'.rical haulage respectively, showing 

 that an annual saving of ;/|'2l40 had been effected by the latter. 

 The total cost of the electrical installation had been CiV^- 



In the second Paper — " Water-Power applied by Electricity 

 to Gold-dredging," by Mr. Robert Hay — an account was given 

 of plant which had been erected in New Zealand to utilise 

 water-power for generating electricity to be transmitted to 

 motors operating a drclge in different portions of a distant 

 river. The plant described had been constructed for gold- 

 dredging in the River Shotover, the course of which was for the 

 most part in rocky gorges through rugged country, accessible 

 only by tracks cut down the leading spurs and gullies. The 

 water was obtained at a creek i* miles distant from the dredg- 

 ing ground, and was brought by a race cut in the side of the 

 hill, or, in places where the ground was not suitable, in a 

 timber-flume, to a pressure tank at a level of 524 feet above the 

 pipes at the generator-house. From this tank to the wheel 

 employed the water was carried in rolled-steel pipes. The prime- 

 mover of the generating plant was a Pellon reaction water- 

 wheel, upon the buckets of which the water, from a nozzle li 

 inches in diameter, impinged at a pressure of 228 lbs. per square 

 inch. This wheel drove two series-wound dynamos working at 

 a normal speed of 700 revolutions per minute, each developing 

 a current of 40 amperes at an electromotive force of 650 volts, 

 or together nearly 70 h.p. The conductors, of a length of 

 two miles, were of No. 4 S. W.G. bare copper wire, and were 

 •npported upon insulators carried by cross-arms upon old 40-lb. 

 rails. The current was conducted to two motors in the dredge, 

 one for driving a centrifugal pump, and the other for operating 

 the buckets, winche.', and revolving cylinder. Two lo-ampcre 

 arc-lamps lighted the dredge at night, and were joined In 

 multiple-series with the motors, with suitable arrangements for 

 their control. The cost of the installation and the weekly 

 working expenses were jCtxx) and jCiS respectively. 



At a recent meeting of the .\cademy of Science of Amster- 

 dam, M. Kamerlingh Onnes presented a paper by M. I,. H. 

 Sitrtsema, on magnetic rotary dispersion in oxygen. Since 

 making a preliminary communication on this subject, the 

 aothor has improved his apparatus in several details, and is 

 now able to examine Ihe gas under a pressure of a hundred 

 atmospheres. The oxygen employed was prepared by electro- 

 lysis. The measurements of rotation .are made by the wcll- 

 NO. 1324, VOL. 51] 



known method in which white light, having passed through the 

 polariser, observing tube, and analyser, is then examined by 

 means of a spectroscope. \ dark band is thus obtained travers- 

 ing the spectrum, and the analyser is turned till this dark band 

 coincides with the part of the spectrum corresponding to light 

 of any desired wave-length. With currents between 35 and 65 

 amperes, the author is able to get rotations of from 3" to 4". 

 In the case of oxygen the results are very well expressed by 



the formula 7 = -?^?^ U + °"°7^°^) where \ is the wave- 



length in thousandths of a millimetre ; the mean error in 7 

 being ± 17-5. This formula is deduced from the formula 



7 = -7 ( " ~ P ^ t" ) where « is the refractive index, given by 



Mascart. A series of measurements were also made on atmo- 

 spheric air, and the values for nitrogen deduced by comparison 

 of these numbers with those obtained for oxygen. The 

 expression thus obtained for nitrogen is as follows : — 

 .y - 560-41 /, ,. o-3Z424 \ 



An interesting series of experiments have been carried on by 

 Mr. T. Andrews, on the influence of stress on the corrosion of 

 melals, which may have considerable practical applications. 

 Bars of iron or steel were subjected to different stresses, ai \ 

 were then placed in some electrolyte — jener.ally a solution cf 

 common salt — and the difference of potential between them 

 measured. It was found that tensile stress caused the produc- 

 tion of an average E.M.F. of 0'0l6 volt between the strained 

 and unstrained bars, the latter being positive. The effect of 

 torsional stress was to produce an average E.M.F. of 0'0I2 

 volt in the same direction. Similar results were obtained with 

 flexional strains. From the data obtained, the author deduces 

 a number of interesting conclusions which bear on the corrosion 

 of iron structures, for which we must refer to the original paper 

 in the Proceedings oi the Institution of Civil Engineers, cxviii. 4. 



The ever-increasing precision in the study of the geological 

 distribution of fossils renders it necessary, from time to time, to 

 recognise that a well-marked litholojical division, though of the 

 greatest value in geological mapping, does not represent a 

 definite time-level, but may gradually rise or fall in time as it is 

 traced along its outcrop. This fact is well illustrated in England 

 by the-Crclaceous beds underlying the true Chalk, and some of 

 the questions involved have been discussed in two recent papers 

 in the Geological Afagaiitie. The first of these, by Messrs. 

 Jukes Browne and Meyer (November, 1894) deals with the 

 Upper Grcensand and Chlorilic Marl. They point out that 

 the latter term has been applied — and may justly be in its 

 lithological sense — to various horizons up to the zone of 

 Belemnilclla plena (as at Beer Head), and they propose that if 

 the name be retained it should be strictly limited to the zone of 

 Staunmema Carleri, which may be regarded as the bottom bed 

 of the true Chalk. They further point out that the well-known 

 Warminster fossils are a mixture of two f.iunas — the majority 

 coming from the summit of the true Upper Greensand, just 

 below Ihe Slai4ronema zone, though some are from that zone 

 itself, Ihe state of preservation being different in the two cases. 

 Thus the confusion between Chloritie Marl and Warminster 

 Greensand is due lo a mixture of fossils from different levels — 

 an accident that has often caused confusion in other formations 

 — and a complete revision of the lists of fossils from these 

 horizons must precede any further correlation. The second 

 paper, by Dr. J. W Gregory (.March, 1895), ''cals with Ihe 

 Gault and Lower Greensand. .\fter considering evidence 

 of various kinds, he comes 10 the conclusion that the conform- 

 able passage from sandy beds into clay rises in time as it passes 

 westward from Kent to Surrey, much as the upper limit of the 



