November 24, 1923] 



NATURE 



769 



This point was again emphasised in the report 

 presented by the Committee on Progress in Lamps and 

 Lighting AppHances, which described efforts being 

 made to effect standardisation of lamps and fittings. 

 Amongst other recent steps ten standard types of 

 lamps suitable for automobile headlights, meeting the 

 requirements of practically all British cars, have been 

 evolved. Mr. L. E. Buckell showed some of the very 

 large gas-filled electric lamps consuming 3000-4000 

 watts and other types with filaments specially designed 

 for projector work. A new feature was the process 

 for spraying bulbs with finely divided china clay ; 

 this gives a soft light and good diffusion, with an 

 absorption estimated not to exceed 7 per cent. The 

 sprayed surface is said to have good wearing properties, 

 and it is believed that these lamps will prove useful in 

 cases where they are unavoidably exposed to view in 

 the direct range of vision and yet it is desirable to 

 avoid glare. Miss Beatrice Irwin gave a demonstra- 

 tion of the colour filter system associated with her 

 name, a variety of lighting units consisting of cylinders 

 of hand-painted parchment paper in pleasing com- 

 binations of colours being shown. 



Leaflet R. 58 received from Messrs. Newton and 

 Wright, Ltd., 471-3 Hornsey Road, N.19, describes 

 the " Harley " unit for dental radiology. The chief 

 feature of the apparatus is in the movements of the 

 X-ray tube, which is a very important feature in 

 practice. Flexibility is here combined usefully with 

 rigidity, and arrangements are made which allow of 

 stereoscopic radiographs being taken. The high- 

 tension transformer is oil - immersed, and when in 



action one pole is earthed ; a separate transformer 

 with the necessary adjustments for the control of 

 the filament current of the Coolidge tube is supplied. 

 In order to vary the penetration of the X-rays, four 

 alternative voltages may be applied to the tube 

 terminals. This appears to be an ample margin for 

 the requirements of dental radiology. 



Messrs. C. F, Casella and Co., Ltd., 49 and 50 

 Parliament Street, London, S.W.i, have issued a 

 new catalogue. No. 523, which contains particulars 

 and illustrations of a very wide range of surveying 

 and drawing instruments and appliances. Detailed 

 specifications are given of the more important instru- 

 ments manufactured by the firm. In the design of 

 several of these, many improvements are embodied, 

 which either give some additional facility to the user 

 or increase the accuracy or length of life of the instru- 

 ment. A notable addition to the list is the new 

 double-reading micrometer theodolite, which has been 

 designed for geodetic and exploration purposes where 

 accuracy of the highest order is desired. In this 

 instrument the diametrical points of the circle are 

 brought together in one field by an optical arrange- 

 ment. It is therefore possible to set the telescope 

 on the object, take the readings of the bubbles and 

 all four readings of the circle without moving from 

 the front of the instrument. The length of time 

 spent in taking a set of readings is thus considerably 

 reduced. This improvement is accompanied by a 

 reduction in the number of parts employed, and the 

 possibility of the instrument being put out of adjust- 

 ment is thereby diminished. 



Our Astronomical Column. 



Reinmuth's Comet, 1923B. — The following two 

 observations, both made at Konigstuhl, are now to 

 hand, the positions being referred to 1923-0 : 



G.M.T. R.A. N. Decl. 



Oct. 31'! gh 22-I"! l'' 15"' 11-36' 22° 26' 36-0' 



Nov. 5 8 15-1 I 17 5090 19 47 23'2 



Mr. Waterfield states, as the result of an unsuccess- 

 ful visual search, that the object is certainly fainter 

 than the nth magnitude. This faintness is probably 

 the reason of the delay in obtaining a third observation. 



The November Leonids. — Mr, W. F. Denning 

 writes : " Very stormy, unsettled weather prevailed 

 during the most of the period when the return of the 

 November meteors was expected, and it was not 

 possible to watch for the shower on several consecutive 

 nights. Mr. I. P. M. Prentice, of Stowmarket, en- 

 deavoured to obtain an early observation of the 

 shower on November 10. For that purpose he carried 

 out a long watch of the heavens commencing at 

 5.55 G.M.T. and ending at 17.55 G.M.T. He recorded 

 82 meteors though the sky was partly cloudy at times. 

 Six of the meteors seen were Leonids with a radiant 

 point apparently at i45°-f22°. If this position for 

 the racliant is confirmed it will indicate that the 

 Leonid radiant, similarly to that of the great Perseid 

 shower of August, is a movable position which 

 advances about i" per day. On November 11, Mr. 

 Prentice saw 35 meteors, but the sky became cloudy 

 before 14.50 G.M.T. and watching had to be dis- 

 continued. At 12.38 G.M.T. he saw a bright fireball 

 directed from a shower of Taurids. It would be 



interesting to get another observation of this if other 

 observers happened to be looking for Leonids on the 

 night of November ii at about 12.38 G.M.T." 



The Extrafocal Method of studying Magni- 

 tudes. — The advantages of this method are the 

 practical equalisation of the size of disc for different 

 magnitudes and elimination of the effect of peculi- 

 arities of images arising from defects in the objective. 

 The quantity measured is simply the density of the 

 image. Mr. Edward S. King (Proc. Nat. Acad. 

 Sciences, U.S.A., Oct. 1923) communicates the results 

 for 100 bright stars from Harvard observations. A 

 yellow screen and isochromatic plates were used, 

 thus giving photovisual magnitudes. The mean 

 excess of the resulting magnitudes over the photo- 

 metric ones is as follows : B - 002, Ao 000, F - 010, 

 G -0x5, K -016, M -020. The following colour- 

 indices were deduced : Bo - 023, Ao - 002, Fo 

 -fo-25. Go -f-o-88, Ko -|-i-28, M -|-i-87. These are 

 independent of visual observations. 



A redi.scussion of the observations of Nova Aquil», 

 1918, when near its maximum brilliance, gives colour- 

 index -0-I9, instead of -0-35, published earlier. 

 Mr. King also measured the colour-indices of the 

 planets by the same method. The values are : 

 Venus -fo-9i. Mars +I-45, Jupiter -^0-96, Saturn 

 (without rings) -f-i-22, Uranus 074. These accord 

 well with the ruddy colour of Mars and the " sea- 

 green " of Uranus. 



The paper also contains new formulae for the effect 

 of phase-angle on the magnitudes. 



NO. 2821, VOL. 112] 



