NATURE 



[December 2^, 1917 



tangentially to the gear blank in the intervals of the 

 reciprocations of the cutter across the face of the blank. 

 This is the principle adopted in the Sunderland generat- 

 ing spur-gear planer, manufactured by Messrs. J. 

 Parkinson, of Shipley, and the article cited contains 

 a fully illustrated description of this machine. 



OVR ASTRONOMICAL COLUMN. 



Comets. — Popular Astronomy for November contains 

 particulars of the appearance of Wolf's comet during 

 the autumn. On October 15 it was readily visible in 

 a 5-in. finder, with a small central non-stellar condensa- 

 tion of the 1 2th magnitude. 



Prof. V. M. Slipher photographed its spectrum at 

 Flagstaff on August 25 and 26. The spectrum was 

 chiefly continuous, even the strongest cometary emis- 

 sions being faint; traces were seen of the cyanogen 

 band at 3883, and of the hydrocarbon band at 4737. 

 The spectrum was too narrow and faint to show the 

 solar lines, but it was evident that the comet was 

 shining almost entirely by reflected sunlight. This is 

 not surprising, considering its great distance from the 

 sun. 



Mr. Viljev has made the unexpected discovery that 

 the object photographed in September, 1916, which was 

 announced as Encke's comet near aphelion, was not 

 really that comet; there are thus at least three occa- 

 sions (January, 1908, September, 1916, September, 1917) 

 when a faint object was detected, nearly in the right 

 position for the comet, and with nearly the right 

 motion, and yet proving to have no connection with 

 it. It brings forcibly before us, what a large number 

 of unknown faint objects (comets or minor planets) 

 exist in the solar system. Mr. Viljev has taken over 

 the computations relating to this comet that were 

 formerly in Prof. Backlund's hands. 



The following ephemeris has been calculated from 

 Mr. Viljev's approximate elements. Perihelion passage 

 will be 19 18 March 24-313 G.M.T. E is the eccentric 

 anomaly. 



G.M.T. E. R.A. Decl. N. log r log A 



1918 ^ h. m. s. . , 



Jan. 1-416 -70 23 o 54 3 24 0-1976 0-2223 



6-o86 68 23 5 8 3 41 0-1804 0-2221 



10-574 66 23 9 44 41 0-1627 0-22 10 



14-880 64 23 14 36 4 23 0-1446 0-2188 



19-008 62 23 19 40 4 48 0-1261 0-2156 



22-961 60 23 24 55 5 15 0-1070 0-2 1 13 



30-357 56 23 35 46 6 II 0-0676 0-2003 



Union Observatory, Johannesburg. — Circular 

 No. 39 of the Union Observatory includes a series of 

 micrometric measures of Eros made between May 15 

 and May 28 of the present year, and a discussion of 

 the advantages of ruling star photographs with lines 

 of right ascension and declination, as compared with 

 the rectangular rulings of the Carte du Ciel. Another 

 excellent example of the photographic maps now being 

 issued from this observatory is included with the cir- 

 cular, and it is shown that from these the places of stars 

 can be obtained with an accuracy which will suffice for 

 most purposes. A further list of nearly 200 proper 

 motions found and measured with the blink-microscope 

 is also given; about fifty of them exceed 20" per 

 century, and many of the displacements are towards 

 the solar antapex. Many of the centennial proper 

 motions deduced, and believed to be trustworthy, are 

 under 10", and one is only 3-2". 



New Zealand Astronomical Tables. — For general 

 information, the Government Astronomer of New 

 Zealand has issued a series of astronomical tables 

 calculated for the meridian of the Hector Observatory 



NO. 2513, VOL. 100] 



{New Zealand Gazette, No. 141). They give the sun's- 

 apparent right ascension and declination, and the 

 Greenwich mean time at apparent noon, as interpolated 

 from the Nautical Almanac, together with the Green- 

 wich date. With the aid of auxiliary tables previously 

 published, the G.M.T. at apparent noon may readily 

 be deduced for any other meridian in New Zealand, 

 and also the approximate times of sunrise and sunset. 



DEVELOPMENT AND USES OF THE 

 STATIC ELECTRICAL MACHINE. 

 A VERY great advance was made in the earliest 

 ■^^ form of electricity generator by the late James 

 Wimshurst in the year 1882. At that time several 

 forms of the Holtz and Voss machines were in use, 

 but their behaviour was most erratic, the slightest 

 moisture in the atmosphere rendered them useless, and 

 under most favourable conditions the output of elec- 

 tricity was small indeed. 



Wimshurst succeeded in producing a machine that 

 would "excite" with certainty under almost any atmo- 

 spheric condition, and by combining a number of 

 plates was able greatly to increase the output. Since 

 then many manufacturers of electrical apparatus have 

 attempted to improve upon it and to convert it into a 

 practical and mechanically efficient generator of elec- 

 tricity. The Medical Supply Association has now 

 placed upon the market what appears to be a 

 thoroughly trustworthy and strong British-made 

 machine that will give, at a moment's notice, a con- 

 tinuous and powerful static discharge. 



The mechanical construction of the machine is 

 simple and very sound. Special attention has been 

 devoted to the plates, which are of vulcanite. By an 

 ingenious method of construction each plate is formed 

 of three sheets of different qualities; this en- 

 tirely stops any tendency to warp, and enables 

 the outer surface to be formed of a very 

 good quality brittle vulcanite that in itself would 

 not bear the high speed of rotation. The whole 

 machine is built upon a cast-iron table, and is run by 

 an attached motor or by any other convenient means ; 

 it is not covered in any way, as the perfection of con- 

 struction is such that electricity is generated 

 immediately on rotating the plates even in the dampest 

 weather. 



The uses of the machine are very numerous. It 

 has been employed with success in agricultural 

 experiments, where greatly increased plant growth 

 under the influence of the static discharge has been 

 recorded. In electro-therapy its value is fully recog- 

 nised, and the static discharge is now in constant use 

 in many hospitals. For the production of X-rays the 

 machine has advantages over the induction coil, the 

 current being unidirectional and continuous. For 

 fluoroscopy or screen work this is a great gain, 

 as the image is bright and absolutely free from flicker. 

 Except where very short exposures are necessary, as 

 in the case of instantaneous radiography, it will do 

 the work as well as, or even better than, a coil. The 

 twelve-plate machine is run at 900 revolutions per 

 minute, and gives a good discharge between balls 8 to 

 10 in. apart; currents from | to i milliampere can be 

 passed through a suitable tube. 



One great convenience of the machine is the complete 

 absence of complicated resistance coils, meters, and 

 other accessories ; no electrical knowledge is demanded 

 in its use ; it is always ready, and it only needs rotat- 

 ing to produce the current. The cost of running with 

 an electro-motor works out at fd. per hour. 



The machine can be seen at the rooms of the Medical 

 Supolv Association, 228 Gray's Inn Road, London, 

 W.C.I. 



