120 



NATURE 



[January 26, 1922 



many cases they violate soirte of the laws of electro- 

 magnetism as stated in curferit text-books. He there- 

 fore pleads for a restatement of these laws in such 

 form that there shall be no apparent exceptions to 

 them. In the first instance, he points out that it is 

 not sufficient for the production of electromotive force 

 by magnetic induction that lines of magnetic force 

 shall cut through a circuit, but that the lines must 

 cut through a conductor. Further, he contends that 

 the existence of the "pinch" effect, contracting the 

 section of a conductor carrying current, of the 

 "stretch" effect, lengthening the conductor, and of 

 what he has named the "corner" effect, when a 

 conductor changes its direction, render it advisable to 

 modify the dictum that the forces on a conductor " can 

 never have a resultant in the direction of the axis." 



The firm of Messrs. Barr and Stroud, which grew 

 out of the remarkable inventive work of the 

 partners, was from 1888 until 19 18 mainly occupied 

 with the manufacture of range-finders and other 

 instruments relating to the gunnery requirements of 

 many different countries. They have since turned 

 their attention also to the small type of internal- 

 combustion engine used on motor-cycles, and, as 

 a consequence, have now put on the market an 

 engine of 349 c.c. capacity working on the four- 

 stroke cycle and having a sleeve-valve and air-cooling. 

 The engine is made under the well-known Burt and 

 McCoUum patents and has several attractive features. 

 The absence of all external valve mechanism makes 

 for cleanliness and greatly lessens engine noise. It 

 is a light engine, since its weight to horse-power 

 ratio Is; it appears, but 7 lb. per h.p. when giving the 

 maximum power of 7 h.p. The sleeve has a double 

 motion, both horizontal and vertical, so combined that 

 any point In it moves in an elliptical orbit. It has 

 five curiously shaped ports, two for inlet, two for 

 exhaust,. and one for the double purpose, serving each 

 in turn. The general design is very attractive, and 

 the claim for a special degree of ease In dismantling 

 and adjusting appears to be substantiated by an 

 examination of the details of the design. Tests on 

 the road have shown a satisfactory degree of fuel 

 economy. 



During the past forty years many proposals have 

 been considered by the authorities in New South 

 Wales for providing suitable means of communication 

 across Sydney Harbour to accommodate the growth 

 and development of Sydney. Tenders and designs have 

 now been Invited for the construction and erection of 

 a cantilever bridge. Some particulars of this project 

 are ^Iven In an illustrated article in Engineering for 

 December 30 last. The bridge will carry four lines of 

 railway, a main roadway 35 ft. wide, a motor road- 

 way 18 'ft. wide, and a footway 15 ft. wide. The 

 total length, Including the approach spans, will be 

 3816 ft. ; the headway required for shipping will be 

 170 ft. at high water for the central 600 ft. of the 

 bridge. The bridge Is to consist of steel cantilevers 

 with shore and harbour arms each 500 ft. long and 

 a central suspended span of 600 ft. The clear span 

 from centre to centre of the main piers will be 

 NO. 2726, VOL. 109] 



1600 ft. For the information of tenderers a number 

 of interesting tables Is given, showing the range of 

 temperatures and intensities of prevailing winds and 

 the extreme velocities and pressures recorded during 

 the severest storms in Sydney. Full particulars are 

 also given regarding the loads to be employed In 

 estimating and the stresses to be used. The specifica- 

 tion has been prepared by the chief engineer, Mr. 

 J. J. C. Bradfield. 



The council of^ the Chemical Society has Issued a 

 pamphlet of eleven pages dealing with the furnishing 

 and equipment (so far as fixed fittings are concerned) 

 of chemical laboratories as the result of a conference 

 of various bodies Interested called by the society 

 eighteen months ago at, we believe, the suggestion of 

 the Royal Institute of British Architects, though this 

 is not mentioned. The object in view was to ascer- 

 tain whether. In view of the high prices of labour and 

 materials, economies could be effected in laboratory 

 fittings. A small committee of the society was ap- 

 pointed and decided to Investigate present practice, 

 and the report gives Information collected from various 

 institutions. Though necessarily but a slight con- 

 tribution to a very large subject, the report contains a 

 useful epitome of the methods in use for forming and 

 treating bench-tops, reagent shelves, fume cupboards, 

 sinks, and waste channels, while notes on ventilation, 

 supply services and floor and wall surfaces are added. 

 Finally, a short bibliography Is given on the subject 

 of laboratories, upon which, however, there is very 

 little literature. Laboratory fittings are always costly, 

 and at the present time, when so much educational 

 work Is held up owing to lack of funds for its material 

 development, any information which will enable those 

 responsible for designing laboratory fittings to cheapen 

 and simplify requirements is bound to be of service. 

 As regards the use of wood particularly, it seems much 

 to be desired that experiments be undertaken in order 

 to ascertain whether many of the cheaper soft woods 

 cannot, by Impregnation or other suitable treatment, 

 be made to serve In place of Imported hard woods. 



The August issue of the Journal of the American 

 Chemical Society contains an account of the separa- 

 tion of the isotopes of chlorine by diffusion, contri- 

 buted by W. D. Harklns and A. Hayes. The work 

 was begun in 1915, and has been carried out In the 

 chemical laboratories of the University of Chicago. A 

 preliminary account of the separation of a heavier 

 fraction from hydrogen chloride by diffusion through 

 the stems of tobacco-pipes was given in Nature of 

 April 22, 1920, p. 230. Calculations by Rayleigh's 

 formula show that to produce an increase of 0-2 in 

 the atomic weight would require the diffusion of 

 130 tons of hydrogen chloride gas. The relative 

 amounts of the different Isotopes are as Important 

 as the atomic weight differences, and It is shown 

 that, contrary to what has been supposed, it is easier 

 to produce a small increase In the atomic weight of 

 chlorine than to produce the same increase in the atomic 

 weight of neon. The diffusion was carried out through 

 clay pipe-stems or tubes at atmospheric pressure. Low 

 pressures would be more advantageous. The increase 



