August 4, 192 1] 



NATURE 



725 



series describing the physical properties of metals, 

 together with a discussion of the relation of these 

 properties to the composition and treatment of the 

 materials. In it are described the properties of nickel 

 and of its commercially important alloys : nickel- 

 steel, ferro-nickel, copper-nickel, and nickel-chromium 

 alloys. The pamphlet is illustrated by numerous 

 photomicrographs and curves, and provided with 

 a very complete bibliography. The collection of data 

 ^ill be valuable to metallurgists. 



The Wireless Press, Ltd., announces for early pub- 

 lication a volume by Prof. J. A. Fleming, who was 

 recently awarded the Albert medal of the Royal 

 Society of Arts in recognition of his many valuable 

 contributions to electrical science. Under the title 

 ^' Fifty Years of Electricity : The Memories of an 

 Electrical Engineer," the work will record the pro- 



gress of electrical engineering since 1870, the year in 

 which Prof. Fleming attained his majority. 



The catalogue of optical instruments recently issued 

 by Messrs. Adam Hilger, Ltd., 75A Camden Road, 

 London, N.W.i, contains details of a number of in- 

 struments not previously obtainable in this country. 

 Amongst theni may be noted a monochromatic illu- 

 minator, an infra-red spectrometer, a vacuum spectro- 

 graph, a linear thermopile, a spectrophotometer, and 

 several refractometers. Messrs. Hilger are offering a 

 limited number of their instruments at a special reduc- 

 tion of 20 per cent, off their current prices. 



Erratum. — We regret that the price of the fifth edi- 

 tion of Sir J, J. Thomson's "Elements of the Mathe- 

 matical Theory of Electricity and Magnetism " was 

 incorrectly given in Nature of July 21, p. 647, as 305. 

 net instead of 255. net. 



Our Astronomical Column. 



Displacement of Lines in the Spectrum of Venus. 



The Astrophvs. Journ. for June contains a paper by 



Dr. Chas. E. St. John and Mr. Seth B. Nicholson, in 

 which thev test the result announced by Mr. Evershed 

 that his Venus spectrograms supported the view that 

 the earth exerts a repulsive effect on the solar gases, 

 analogous to that which the sun appears to exert on 

 comets' tails. The authors took two series of Venus 

 spectrograms : in 1919 with Venus east of the sun, 

 and in 1919-20 with Venus west of the sun. Their 

 analysis of the results leads them to conclude that the 

 effect can be correlated with the altitude and the 

 angular diameter of Venus; hence they conjecture 

 that it is due to atmospheric dispersion, the centre of 

 the visual image which was adjusted on the slit 

 differing from the centre of the photographic image. 

 Thev propose in future to take some further plates 

 viewing the image through a blue screen, which 

 should eliminate the above source of error. They have 

 incidentallv examined the measures to see if they 

 afford any evidence of a rkpid rotation of the planet, 

 but conclude that "the difference between the morn- 

 ing and evening series ... is not of an order that 

 would indicate ... a rate of rotation higher than 

 that found bv Slipher." In all the plates of the 

 series, whether on Venus, the sky, or the sun, an 

 iron-arc spectrum was photographed simultaneously. 



Planetary Photography. — Pubns. Ast. Soc. Pacific, 

 June, 192 1, contains a lecture by Mr. E. C. Slipher 

 on this subject, illustrated by numerous reproductions 

 of photographs of Venus, Mars, Jupiter, and Saturn. 

 Those of Venus failed to record any surface markings, 

 but illustrate the changes of diameter and phase that 

 occur in the synodic period. The photographs of Mars 

 taken at Flagstaff are stated to number 100,000. 

 Numerous exposures are made on each plate, in the 

 hope that some will catch the moments of best defini- 

 tion. Mr. Slipher gives a long list of features that 

 he claims can be verified from the plates. It must, 

 however, be admitted that not all of these can be seen 

 on the reproductions, though they may be visible on 

 the original negatives. The polar cap is shown with 

 great clearness, and it would seem to be worth while 

 to make measures of its position angle in order to 

 obtain an independent determination of the position 

 of the axis. 



The photographs of Saturn yield much interesting 



NO. 2701, VOL. 107] 



information. The great excess of luminosity of ring B 

 over ring A, and the semi-transparency of the latter, 

 permitting the outline of the ball to be seen through 

 it, are well brought out ; also the faintness of the 

 ring when the sun is near its plane. There are repro- 

 ductions of two exposures on April 28 last, when the 

 earth and sun were on opposite sides of the ring- 

 plane. There is a dark stripe across the centre of the 

 disc, formed by the dark side of the ring and its 

 shadow ; it is narrowest in the middle, the two edges 

 being curved in opposite directions. One feature 

 shown in all the photographs is the extreme regularity 

 of the fivefold belt in Saturn's southern hemisphere. 

 The edges appear to be exactly parallel to the equator. 

 One is inclined to mistrust this regularity on drawings, 

 but the photographs are free from bias. 



Measurement of the Diameter of Arcturus. — Mr. 

 F. G. Pease (Pubns. Ast. Soc. Pacific, June, 1921) 

 gives an account of the work with the interferometer 

 on the loo-in. Hooker telescope at Mount Wilson since 

 j the successful measurement of the diameter of Betel- 

 i geuse. Observations on Arcturus in February and 

 ■ March, with poor seeing, showed some diminution of 

 i the visibility of the fringes with increasing distance 

 I between mirrors. At length on April 15 the seeing 

 j was perfect, and the fringes were found to disappear 

 when the mirrors were separated by 19-5 ft. As the 

 maximum separation at present is 20 ft., it was not 

 : possible to proceed to the next point of greatest 

 visibility of fringes ; but the value 195 is considered 

 ; to be correct within 05. Assuming an effective wave- 

 i length for type Ko as 5600, the angular diameter of 

 ; Arcturus is 00237", very near the mean of the values 

 ! estimated by Eddington, Russell, and Hertzsprung. 

 I The parallax is taken as 01 16' from the mean of 

 I the best recent measures, giving a linear diameter of 

 19,000,000 miles, or twenty-two times that of the sun. 

 j Observations of Aldebaran on nights of poor defini- 

 i tion give grounds for thinking that its angular dia- 

 meter is somewhat greater than that of Arcturus ; 

 Pollux and a Ceti give indications of weakened 

 fringes, but probably a longer beam than 20 ft. would 

 be needed to make them disappear. The mirrors 

 have hitherto been moved by hand, which has taken 

 much time. Two screws driven by a single motor 

 are now being mounted, which should greatly facili- 

 tate the measures. 



