NOTES 121 



awarded prizes for the best papers submitted to them and that, under the scheme, 

 this incentive to research might disappear. Obviously, however, this difficulty 

 might easily be overcome if each society retained the right to print any papers 

 sent to them irrespective of their ultimate fate at the hands of the Board. A 

 more serious objection is that a paper is usually written for a particular class of 

 reader. A treatment suitable for the Physical Society would probably not be best 

 for the Iron and Steel Institute. Having regard to this fact it seems probable 

 that a Central Board would find its most important function in issuing a weekly or 

 monthly list of forthcoming papers with intelligible abstracts, as suggested by 

 Prof. Schuster. 



Since Tyndall made his famous experiments in 1872 it has been assumed that 

 the light scattered by dust-free air is too faint to be observable with the small 

 thicknesses which can be used in the laboratory ; although it has been well 

 established that air molecules are competent to produce such scattering. Prof. 

 Strutt has, however, recently succeeded in demonstrating the effect experimentally. 

 He states that the chief essentials for success are to avoid, as far as possible, stray 

 light diffused from the walls of the vessel used and to observe the beam transversely 

 against the blackest possible background. He employed a cross-shaped vessel 

 made of brass tubing of i| in. diameter, painted dead black inside. A beam from 

 an arc was directed down one cylinder, being admitted through a quartz window, 

 while one-half of the other cylinder formed a black cave against which the beam 

 was viewed through a glass plate covering the end of the other half. The air 

 was dried and then filtered through a tube 4 ft. long filled with cotton wool. It 

 was forced into the vessel under pressure, so that while dust-free air might leak 

 out, ordinary air could not leak in. Viewed as described there was a blue track 

 along the beam which, though much fainter than the track seen with ordinary air, 

 was visible without difficulty when the eyes had been rested in the dark. Several 

 tests were applied to show that the effect observed was not due to residual dust. 

 No change was produced by further filtering, and Aitkens' method for counting 

 dust particles failed to reveal presence of a single one. The blue track was 

 examined spectroscopically to eliminate the possibility of the effect being due to a 

 fluorescence of the air. A two-hours' exposure with the arc source brought out 

 faintly the cyanogen band (X388), which is photographically the most conspicuous 

 feature of the arc spectrum ; while a three-days' exposure with a quartz-mercury 

 lamp showed only the mercury lines. Other gases were used in the vessel in place 

 of air. With oxygen the appearance was indistinguishable from that with air, with 

 carbon dioxide the intensity was greater than with air, and with hydrogen very 

 faint indeed. The scattered light is almost completely polarised in the manner 

 indicated by theory. The experiments described are preliminary to the quantitative 

 measurements which are now in progress. 



The state of affairs in Russia makes the discovery of platinum in the Serrania 

 de Ronda, in the south of Spain, announced in a special memoir issued by the 

 Geological Institute of Spain, specially interesting. The rocks in this region were 

 studied because of their similarity to the platinum-bearing rocks in the Ural 

 Mountains. The Ural deposits yielded in pre-war days about 300,000 oz. (troy) 

 per annum — about 95 per cent, of the world's yearly output. In 1916 this figure 

 had fallen to 86,000 oz. Platinum has also been found in some quartz deposits in 

 the Ober Rosbach district of the Taunus Mountains (Germany), and these deposits 

 are being worked {Nature, April 25, 1918). The chief source of the Entente 

 supplies is now presumably the mines in Colombia, where the metal was first dis- 

 covered in 1735. Their output is comparatively small : in 1916 it was 25,000 oz., 



