October i8, 19] 



NATURE 



comparators consist of a heavy cast-iron base, on the 

 back of which micrometer microscopes are fixed. The 

 bars, to be compared, are mounted in a moving car- 

 riage, which is traversed to and fro beneath the micro- 

 scopes, thus enabling plus and minus difference read- 

 ings to be taken. In this case the moving carriage 

 consists essentially of a double tank mounted on 

 wheels. The two standards are carried on light beams 

 in the inner tank, which beams are fitted with accurate 

 levelling screws. The inner tank is filled with water, 

 so as to maintain the standards at a constant tem- 

 perature, whilst a complete system of thermometers 

 enables the temperature accurately to be determined. 

 The outer tank acts as a jacket to the inner. By 

 filling the interspace with ice, or, alternatively, hot 

 water, coefficients of expansion can be obtained to a 

 high degree of accuracy. In the general design and in 

 the supply of the detail fittings, the utmost precautions 

 have been taken to eliminate small sources of error, 

 and an accuracy of about ±o-i fx is anticipated after 

 final erection. These instruments were constructed by 

 the Soci^td Genevoise, of 87 Victoria Street, London, 

 and Geneva, to the specification of Mr. O. Paul 

 Monckton. 



The September number of La Science et la Vie 

 contains a description of the stereoradioscope invented 

 by Major Lievre, of the French Army Medical Corps. 

 The principle of the apparatus is as follows. A body 

 acted upon by the Rontgen rays emanatiag from two 

 different sources distant from 6 to 10 centimetres from 

 each other projects two parallel shadows on to the 

 screen. If by a suitable arrangement the right eye 

 is made to see only one of the images at the sarne 

 time as the other image is seen by the left eye only, 

 an observer will have a stereoscopic view of the radio- 

 scopic image. To dissociate the two images in this 

 manner and render each visible to the corresponding 

 eve, Major Lievre has applied the principle of the per- 

 sistence of luminous impressions on the retina. The 

 apparatus itself consists of three essential parts super- 

 posed, viz. a double source of X-rays underneath, fal- 

 lowed by the usual screen, then a sighting device pro- 

 vided with a shutter and a commutator. The commu- 

 tator serves the purpose of operating one of the X-ray 

 tubes simultaneously with the uncovering of one of the 

 eyepieces, and of shutting off the other X-ray source 

 and closing the shutter of the other evepiece. The 

 device, which has been adopted by the French Armv, 

 has the advantage of great mechanical simplicity aiid 

 ease of application. 



The problem of the landing of an aeroplane in the 

 shortest distance and with the minimum of shock is a 

 very important one in aviation, especiallv with the 

 advent of the heavier machines of the bombing type. 

 In a verv interesting article in the September number 

 of La Science et la Vie M. Jean Fontanges deals with 

 the question, and describes the svstems of landing car- 

 riage employed on various French and German 

 machines. The type of carriage provided with skids 

 only is now practically obsolete, the most usual pattern 

 consisting either of v^-heels alone, or wheels in con- 

 junction with skids, or a rear crutch. The centre or 

 supporting wheels have to be built on a high-strength 

 framework (usually of steel tubing), wnth (smaller) 

 front wheels to prevent the machine landing nose 

 down. Some of the types are provided with brakes 

 on the wheels, to give quicker landing. Mention is 

 made of the Paul Schmitt biplane, which is provided 

 with a device for altering the incidence of the wmgs 

 and so reducing the speed of the machine prior to 

 landmg. The article also discusses the types of shock- 

 absorber usually employed. 



NO. 2503, VOL. 100] 



Mr. G. Burto.n Baker contributes to the Chemical 

 News for September 21 an interesting note on a colour- 

 ing matter extracted from Wasahba wood. The latter 

 has a specific gravity 1-214; it is difficult to work, 

 being extremely hard and almost bony in texture. 

 When the sawdust is extracted with hot alcohol a 

 colourless solution is obtained which becomes a bright 

 salmon-pink when treated with an alkali solution, the 

 colour being discharged by acids. If the alcoholic 

 extract is used side by side with a one per cent, solu- 

 tion of phenolphthalein in the titration of ammonia, 

 potassium hydroxide, and sodium hydroxide solutions 

 with hydrochloric acid, the same result is ob- 

 tained in the case of potassium hydroxide as with 

 phenolphthalein, whilst with ammonia and sodium 

 hydroxide the results were approximately the same. 

 Concordant results could not be obtained when sodium, 

 potassium, and ammonium carbonates were the alkalis 

 employed. Further, the red alkaline solution will act 

 as a dye, staining white pine quite deeply. 



The issue of Engineering for September 21 contains 

 an account of the hydraulic power undertakings con- 

 nected with the town of Barcelona and its electric 

 supply. Under the control of the Barcelona Traction, 

 Light, and Power Co. there has been inaugurated a 

 threefold development of the hydraulic resources of the 

 adjacent country. Power accessible to the extent of 

 60,000 h.p., under a head of 164 ft., is already obtained 

 from the river Segre, from Lerida downwards for a 

 distance of 18^ miles. By the formation of a dam, 

 262 ft. high, a reservoir has been formed on the river 

 Noguera Pallaresa, giving a head of 492 ft., from 

 which two power stations of 50,000 and 60,000 h.p. 

 respectively are supplied. The river Ebro is to yield 

 the third quota, a dam 1378 ft." long and 197 ft. high 

 being contemplated, and this will enable its power 

 station to develop no fewer than 300,000 h.p. The 

 Noguera Pallaresa dam has only recently been com- 

 pleted. It impounds a volume of 6,909,000,000 cub. ft. 

 It is constructed across the narrowest part of the valley 

 and is curved to a radius of 984 ft. The dani is a 

 gravity dam, with a volume of 9,500,000 cub. ft. The 

 Tremp power-house is situated about half a mile below 

 the dam, and has four turbines, which run under a 

 maximum head of 229 ft. and a minimum head of 

 98 ft. 



Mr. Hvmphrey Milford, of the Oxford University 

 Press, announces " Studies in the History and 

 Methoid of Science," edited by C. Singer. It will con- 

 tain the following contributions: — "The Scientific 

 Views and Visions of "St. Hildegarde," C. Singer; 

 "Vitalism," Dr. J. W. Jenkinson ; "A Studv in Earlv 

 Renaissance Anatomy," C. Singer; "The Blessing of 

 Cramp Rings," R. Crawford; "Dr. John Wever and 

 the Witch Mania," E. T. Withington ; "The ' Tractatus 

 de Causis et Indiciis Morborum,' attributed to Mai- 

 monides," R. Levy; "Scientific Discovery and Logical 

 Proof," F. S. Schiller. Mr. Milford will also pub- 

 lish "The Determination of Farming Costs," bv C. S. 

 Orwin. 



The October list of Publishers' Remainders of Mr. 

 H. J. Glaisher, 55 Wigmore Street, W.i, is miscel- 

 laneous m character, and should be seen by those in 

 search of books in new condition at low prices. Among 

 the books likely to be of interest to readers of Nature 

 are Sir F. Galton's "Memories of Mv Life"; "The 

 Life of Sir Joseph Banks"; "The Life and Work of 

 Prof. C. Pritchard"; and "Eleanor Anne Ormerod : 

 Autobiography and Correspondence," all of which are 

 listed at a very low figure. The " Librarv of Useful 

 Knowledge "—a series of shilling volumes— is offered at 

 half-price. 



