June 3, 1920] 



NATURE 



435 



of impurities which might reveal the modes of manu- 

 facture. Reference is made to the Central Laboratory 

 of the British at Hesdin under the late Prof. Watson, 

 and the great rapidity with which new enemy materials 

 were detected is attributed to the excellent camara- 

 derie which always prevailed between the French and 

 British Gas Services. The article also contains a 

 summary of the report of the French Mission on 

 the chemical works in the area of occupation, includ- 

 ing statistics of the output. In conclusion, M. 

 Florentin expresses the hope that the war has demon- 

 strated the inseparability of chemistry and national 

 defence and the importance of developing the 

 scientific and industrial research which was initiated 

 in France by gas warfare. 



We have received from Messrs. Wood Bros. Glass 

 Co., Ltd., of Barnsley, a copy of their catalogue of 

 English chemical glassware. The list of apparatus is 

 a comprehensive one, well-arranged and neatly illus- 

 trated. Judging by the particulars given, chemists 

 should have no difficulty in obtaining any of the usual 

 flasks, beakers, burettes, gas pipettes, absorption tubes, 

 or other glass instruments employed in the laboratory 

 from the selection offered ; and as regards any spyecial 

 apparatus in glass that experimenters may want the 

 makers invite inquiry. Messrs. Wood are old-estab- 

 lished glass manufacturers who took up the making of 

 chemical glassware in 1915, and they claim that, fol- 

 lowing the indications given by Sir Herbert Jackson's 

 work on the composition of various special kinds of 

 glass, supplemented by the investigations of their own 

 staff, they are able to produce ware superior to the 

 best Jena glass in its resistance to the action of strong 

 chemicals. It does not withstand sudden extreme 

 changes of temperature quite so well, but will, it is 

 claimed, stand being plunged whilst at a temperature 

 of 150° C. into cold water, and this is more than 

 sufficient for all ordinary requirements. The shapes 

 and designs of ware adopted are those approved by 

 the Glass Research Committee of the Institute of 

 Chemistry, and it would appear generally that the 

 aim of the makers is the praiseworthy one of pro- 

 ducing apparatus of high quality in close relation to 

 scientific needs. A feature is made of standard volu- 

 metric apparatus verified and stamped by the National 

 Physical Laboratory. 



Mr. S. Evershed read a paper on permanent mag- 

 nets in theory and practice to the Institution of 

 Electrical Engineers on May 13. He practically 

 adopts Ampere's theory that the molecules of iron 

 in a magnet are equivalent to electric circuits of no 

 resistance in which electric currents are always flow- 

 ing. On this hypothesis, and adopting Hopkinson's 

 formula connecting magneto-motive force, reluctance, 

 and flux, he discusses the design and predetermina- 

 tion of permanent magnets. He points out that 

 since in practice the demagnetisation curve of the 

 steel is known, the problem that has to be solved 

 is to find the shape of the minimum volume of 

 steer required to produce a given quantity of external 

 magnetic energy. By "making assumptions as to 

 the reluctance of the paths of the magnetic 

 flux, Mr. Evershed proves that the performance 

 NO. 2640, VOL. 105] 



of a permanent magnet can be predicted in certain 

 cases with accuracy. We are not sure, however, 

 whether this is due to the fact that the errors made 

 in his assumptions cancel out one another. We 

 fail to understand his formula for the magnetic con. 

 ductance between two spherical poles. It would be 

 true if they were at an infinite distance apart, but 

 appreciable errors come in when the distance be- 

 tween them is less than a hundred times the radius 

 of either. It is easy to show that the magnetic con- 

 ductance between two spherical poles equals \t: tim6s 

 the electrostatic capacity between their surfaces. 

 Hence, as the electrostatic capacities have been tabu- 

 lated, the magnetic conductances could be written 

 down at once with high accuracy. From the en- 

 gineering point of view the paper is valuable, as the 

 subject is of practical importance to manufacturers. 



Prof. W. W. Watts, lecturing to the South 

 Kensington Branch of the National Union of Scientific 

 Workers on May 27 on "The Evolution of the 

 Bicycle," showed that the development of this, as of 

 any mechanical apparatus, took a similar course to 

 that observed in biological evolution. It was largely 

 a process of trial and error; advance was usually in 

 small details of specialisation, and, as in the case of 

 the high bicycle, development was apt to take place 

 in a "blind lead" by following out a wrong principle. 

 The lecture will be reported in the next issue of the 

 Scien-tific Worker, copies of which can be obtained 

 from the Secretary, N.U.S.W., 19 Tothill Street. 

 S.W.I, by sending a stamped addressed envelope. 



Kodak, Ltd. (Wratten division), have just issued a 

 new series of nine circular light-filters to facilitate 

 visual work with the microscope. They are 35 mm. 

 in diameter, and so fit the standard turn-out ring 

 usually available in sub-stage fittings. Six are for 

 increasing the contrast in stained or coloured pre- 

 parations, one is blue and serves for getting the 

 highest resolving power, one a neutral tint for 

 modulating the intensity of the illumination, and the 

 ninth converts the light from metal filament vacuum 

 lamps into the equivalent daylight. This last is also 

 of service with other light sources, such as the new 

 thorium pastille gas lamp and the usual paraffin 

 lamps. Its use gives the same colour values as day- 

 light, and so reduces or eliminates eye-strain when 

 observations are long continued. 



In a small leaflet entitled "Radium Facts," received 

 from Messrs. Watson and Sons, are collected 

 numerous data relating to radio-active substances 

 useful to intending purchasers. From it we learn 

 that, whereas the total production of radium to date 

 by the Standard Chemical Co., of Pittsburgh, was 

 50 grams of radium element, its present output is 

 at the rate of 18 grams of the element per annum. 

 We understand that this output could be increased to 

 50 grams of radium element yearly if the demand for 

 such a quantity should arise — a very considerable 

 national asset. It is interesting to observe that the 

 present total available supply of high-grade purity 

 radium in the world is estimated to be about 

 120 grams. 



