322 



■NATURE 



[November 4, 1920 



rent of which is measured by an ordinary direct- 

 current milliamnieter. With the help of this instru- 

 ment the measurement of very minute alternating 

 currents and pressures is as simple as everyday 

 measurements with ordinary voltmeters and am- 

 meters. By its use absolute measurements of induct- 

 ances and capacities are made in a few minutes with 

 a maximum inaccuracy of about i in looo. By the 

 use of suitable electrical " filters " very approximately 

 sine-shaped waves are obtained by blocking out the 

 disturbing harmonics. The authors have shown 

 recently in the same journal how the frequency of 

 the alternating currents can be determined with high 

 accuracy. Its sensitiveness is shown by the fact 

 that it can measure, by means of a direct reading of 

 the pointer, the capacity of a sphere one millimetre in 

 radius. The instrument has very many useful 

 applications. 



Some comments on the statistics just issued by 

 Lloyd's Register for the quarter ending on Septem- 

 ber 30 appear in Engineering for October 22. Before 

 the war the merchant tonnage under construction in 

 this country usually exceeded the total building in 

 all other countries in the world ; at present che 

 tonnage building abroad exceeds our tonnage under 

 construction by about 103,000 tons. At the end of 

 September the vessels building in this country num- 

 bered 961 with a total gross tonnage of 3,731,098, 

 an increase during the year of more than 32 per cent. ; 

 in comparison with the figure for September, 1913, 

 the increase is more than 90 per cent. The individual 

 tonnage in no case exceeds 25,000. With regard to 

 the tonnage building abroad, the most noticeable 

 feature is the decline in the tonnage building in the 

 United States, where there are now only 312 vessels 

 with an aggregate gross tonnage of 1,772,193 in hand, 

 as compared with 767 vessels and a gross tonnage of 

 3,470,748 for the corresponding quarter of last year. Of 

 the vessels now under construction, 114 with a total 

 gross tonnage of 796,060 are intended for carrying 

 oil in bulk. The United States is building 79 of 

 these ships, and there are 32 building in the United 

 Kingdom. Only five small steamers are being con- 

 structed of reinforced concrete in the United King- 

 dom, their total tonnage amounting to 2354 ; eleven 

 vessels of this type are being built abroad, having a 

 total tonnage of 24,069. 



The miscellaneous catalogue (No. 2, 1920) of 

 second-hand books just issued by Mr. W. H. Robin- 

 son, 4 Nelson Street, Newcastle-upon-Tyne, contains 

 nearly a thousand items, about two hundred of which 

 deal with scientific subjects. The prices asked for the 

 works appear very reasonable. The catalogue can be 

 obtained upon application. 



We have received from the firm of Scientific 

 .Appliances, Southampton Row, W.C.i, a copy of its 

 illustrated catalogue, which shows the apparatus 

 available in two sections of the establishment. 

 Section E contains electrical and magnetic apparatus, 

 and fittings such as telephone sets, lighting sets, 

 Wimshurst machines, accumulators, etc. Section O 

 comprises optical appliances and drawing materials. 

 NO. 2662, VOL. 106] 



Our Astronomical Column. 



Comets. — Dr. Kudara, who rediscovered Tempel's 

 second comet last May, gives the following revised 

 elements for it in Popular Astronomy for October. 

 He also gives the corrected R..A. for the observation 

 on May 25 last as 22h. 5sm. 43-7S. : 



T = 1920 June 16-196 G.M.T. 

 «) = 186' 39' o"\ 

 a = 120° 46' 5" 



7= .2= 45' .lr9^°'° 



(t>= 33° 54' 21") 

 li =687-51" 

 log a =0-47515 



The period is the shortest of any known comet with 

 the exception of that of Encke. 



Popular Astronomy also contains the following 

 elements of Borrelly's comet (1905 II.) deduced by 

 Mr. F. E. Seagrave from observations on 1918 Octo- 

 ber 9 and December 6 and 1919 February 4 : 



</> = 37° 57' II" 

 /I = 5 14-023' 



log " = 0559350 



T = i9i8 Nov. 168632 G.M.T. 

 <i> =352° 23' 32" 

 ri= 76° 57' 2" 

 i = 30° 29' 14" 



Mount Wilson Observations of Capella. — Some 

 account of the remarkable observations of Capella as 

 a double star at Mount Wilson, using interferometer 

 methods on the loo-in. equatorial, was given in 

 Nature last April. The Astrophysical Journal for 

 June contains further details; the theory of the inter- 

 ferometer is described by Mr. A. A. Michelson, while 

 Mr. J. A. .Anderson discusses the observations of 

 Capella, and finds the orbit from observations on six 

 days ranging from 1919 December 30 to 1920 .April 23, 

 combined with the spectroscopic data. The following 

 are the adopted elements: Period =104-006 days; 

 periastron = Julian day 24223879; = 005249" = 

 130,924,000 km.; e=ooi6; 1=140° 30'; tD= 117-3°; 

 parallax = 00600" ; masses of components in terms of 

 sun, 462 and 365. These elements satisfy the ob- 

 servations with no error exceeding 000004" in distance 

 and 09° in position-angle, but the author points out 

 that a longer series would probablv show much larger 

 residuals, since the interferometer multiplies the 

 theoretical resolving power by 25 only. 



From the close resemblance of the spectrum of one 

 of the components with that of the sun it is probable 

 that the surface brilliancy is much the same as the 

 sun's, in which case the diameter of each star would 

 be of the order of ten times that of the sun, ojr one- 

 tenth of the distance between them. It is noted that 

 the visual magnitudes of the two components must be 

 very nearly the same, since the interference fringes 

 completely vanished on superposition. 



Variation in the Light of Jupiter. — A novel use 

 of the photo-electric cell was made bv Herr P. 

 Guthnick at the Berlin-Babelsberg Observatory 

 in an investigation as to whether the light of 

 Jupiter showed any variation in the course of 

 the planet's rotation owing to different markings 

 being presented to us. In fact, last December 

 and January there was a distinct variation having 

 an amplitude of 014 magnitude. However, this 

 rapidly diminished, and by February was only 

 004 magnitude. The author remarks that this rapid 

 change gives support to the temporary variability in 

 the light of Neptune in a period of eight hours ob- 

 served by Prof. Hall and discussed in Monthly Notices, 

 vols. xliv. and Ixxv. Unfortunately. Neptune is too 

 faint for observation with the photo-electric cell, other- 

 wise a determination of its rotation-period might 

 result. 



