July 15, 1920] 



NATURE 



62^ 



filament current and plate potential are both provided 

 by means of transformers. The author finds that, 

 operated in this way, the triode tube gives results 

 which compare favourably with those obtained with 

 the usual direct-current method, and that it has the 

 advantage of not requiring a high-voltage generator 

 or battery, while over a limifed distance signals may 

 be received with a non-oscillating detector. A more 

 complete account of this work is to appear as a 

 Scientific Paper of the Bureau. 



Mr. S. J. Peachey, lecturer in chemistry at the 

 <I;olleg-e of Technology', Manchester, claims to 

 have discovered a process for the cold vulcanisation 

 of rubber. This is applicable not onlv to rubber in 

 its solid forms, but also to solutions. The final pro- 

 duct may be obtained containing no free sulphur. 

 Leather waste, wood-meal, and starch cellulose may 

 be mixed with rubber so as to yield cheap, fully 

 vulcanised products with new properties and great 

 durability. Leather waste and rubber may be con- 

 verted into a product resembling- leather, and at the 

 same time waterproof. No details of the process are 

 given beyond the fact that it employs "two gases 

 which are by-products of several chemical manufac- 

 turing processes, and are available at a very low 

 cost." If these claims can be substantiated, it 

 appears that the process should be one of very great 

 technical interest and importance. 



Facility of manipulation and precision in adjust- 

 ment are two prime features in X-ray tube stands. 

 They appear to have been carefully considered in the 

 models Mark IIL and Mark IV. which we find in 

 Bulletin 255 of Messrs. Watson and Sons, Ltd. In 

 the screen attachment to the latter model there is an 

 arrangement whereby the X-ray tube and the screen 

 move together during vertical examinations. We 

 would suggest that a valuable addition to the illus- 

 trations of these models would be the protective 

 devices to be employed with them. It is especially 

 necessary during screening examinations to avoid 

 stray radiation reaching the operator, and the adop- 

 tion of rigorous, protective measures would no doubt 

 become more general if publicity were given to this 

 requirement. 



In the course of an article on Pelton-wheel con- 

 struction by Mr. Percy Pitman, in Engineering for 

 June 25, the author describes the method adopted for 

 improving the jets, which were unsatisfactory in the 

 existing turbine. Experimental nozzles were made in 

 fluid-pressed bronze, and four rustless steel blades, 

 5 mm. thick, were dovetailed into them so as to lie 

 in axial planes. These blades were ground and highly 

 polished up to a thin knife-edge. A great improve- 

 ment resulted ; the jets were of extraordinary solidity 

 and transparency, the water for about 2 ft. issuing 

 almost like a glass rod. Those interested in the 

 design of Pelton-wheel buckets will find a good deal 

 of useful information in this article ; there is but 

 little of practical value in text-books, and the author 

 gives the complete lay-out of the new buckets, and 

 includes copies of the workifi<f drawings. 

 NO. 2646, VOL. 105] 



Our Astronomical Column. 



An Easy Method ok Finui.sg Latitude.— The 

 Observatory for June contains an article by N. Liapin 

 on a method of finding latitude which is interestmg 

 and a useful exercise lor astronomical students, and 

 requires no other instrument than a watch. The 

 method consists simply in observing the number of 

 seconds between first and last contacts of the sun 

 with the horizon at sunrise or sunset. The formula 

 for solution given by the author is cos' latitude = 

 sin" (sun's decl.) + 4 (sun's radius)' /(time interval)', 

 where the radius and time interval must be expressed 

 in the same units. This formula does not take 

 account of the change of sun's decl. in the interval; 

 a correction for this may readily be made. 



Five acfual determinations by this method are 

 given, the resulting latitude being 10' from the truth. 

 While a sea horizon is preferable, any straight and 

 level horizon will serve. 



Increasing the Photographic Power of Tele- 

 scopes. — In the Proceedings of the U.S. National 

 Academy of Sciences for March Dr. Shapley describes 

 a method of increasing the photographic power of 

 large reflectors for the purpose of photographing 

 extremely faint objects. The faintest stars at present 

 reached by the 60-in. reflector are of magnitudes 20 

 to 21, and it is believed that the great Hooker tele- 

 sco{>e will gain about one magnitude over this. Dr. 

 Shapley is of the opinion that this is bordering on 

 the limiting magnitudes in globular clusters, and if 

 one or two fainter magnitudes were available for 

 study, some most important information might be 

 obtained with regard to several questions of stellar 

 and galactic evolution. The method employed is 

 quite simple, consisting essentially in shortening the 

 effective focal length of the telescope by means of a 

 short focus lens placed between the mirror and the 

 plate. The brightness of the image is thus increased, 

 though, of course, a reduction of scale is inevitable. 

 This, however, is immaterial in many sidereal prob- 

 lems. A trial series of exposures with different inten- 

 sifiers seems to have yielded satisfactory results, and 

 questions relating to globular clusters, the limits of 

 the galactic svstem, and similar problems appear to 

 be more hopeful of solution. 



A New Spectropvrheliometer and Solar Measure- 

 ments MADE WITH IT. — In No. 378 of the Scientific 

 Papers of the U.S. Bureau of Standards, recently 

 issued, Messrs. W. W. Coblentz and H. Kahler give an 

 account of a new spectropyrheliometer and measure- 

 ments of the component radiations from the sun and 

 from a quartz-mercury vapour lamp. The spectro- 

 pyrheliometer consists of a quartz spectrograph and 

 cylindrical condensing lens placed upon an equatorial 

 mounting, thus eliminating the ultra-violet absorption 

 produced in heliostat mirrors. The paper sums up 

 the data given on the relative components of infra- 

 red, visible, and ultra-violet radiation from the sun 

 and from a quartz-mercury arc lamp, also on 

 the gas-filled tungsten lamp, the iron arc, and the 

 carbon arc. In the first appendix methods are given 

 for excluding ultra-violet light from buildings, one of 

 these being the use of a kind of Venetian blind or 

 louvre of wide slats, painted buff to reflect the light into 

 the building, the buff or red paint absorbing the ultra- 

 violet, thus protecting the contents of the building 

 (balloon hangars, etc.) from photochemical action. 

 The second appendix suggests methods for protecting 

 projection lantern films from the heat of the lamp, 

 and a simple method put forward is to provide the 

 water-cell with windows of Corning " heat-absorbing " 

 glass, which is very opaque to infra-red radiation. 



