October 29, 1903] 



NATURE 



631 



Recent Spectrographic Observations of Nov^. — 

 Using the slitless spectrograph recently attached to the 

 Crossley reflector, Prof. Perrine has obtained photographs 

 of the recent spectra of various novze. 



A spectrogram of Nova Aurigae, taken with a total ex- 

 posure of 5 hours on August 29 and 30, shows that 

 important changes have taken place in the spectrum of 

 this star since 190 1, when the spectrum was photographed 

 by Mr. Stebbins. At that time the chief nebular line at 

 A 501 was equal in intensity to the lines at A 462, A 434, and 

 H5, but in the recent photographs it is entirely absent ; 

 the other lines are relatively the same, but all appear to 

 have decreased in intensity with regard to the continuous 

 spectrum. This Nova is now of the fourteenth magnitude. 



In the case of Nova Persei, a spectrum obtained on July 

 30, with an exposure of 2 hours 3 minutes, shows that 

 striking changes have taken place since March, 1902. H3 

 has decreased greatly in brightness during the interval, and 

 the condensation at A 434 has also become less marked, 

 whilst H8 has only suffered the normal diminution in bright- 

 ness. The lines at A 339 and A 346 show the greatest 

 changes, the former having entirely disappeared, whilst the 

 latter is barely distinguishable on the latest spectrogram ; 

 the chief nebular line does not appear to have changed 

 relatively to the general spectrum. On July 30 the magni- 

 tude of Nova Persei was about 11-5 or 12. 



Even in the more recent Nova Geminorum important 

 changes are already noticeable ; photographs were secured 

 on August 28, 31, and September 2, and when compared 

 with the observations of ^iay 11 it was seen that during 

 the interval of 3J months the whole spectrum had become 

 much weaker ;' the chief nebular line had become much 

 stronger, whilst H/3 had greatly decreased in relative in- 

 tensity. The line at A 434 is by far the strongest in the 

 whole spectrum, and that at A 463 is much broadened and 

 probably composite ; there are also indications of the higher 

 hydrogen lines on the background of continuous spectrum. 

 On a number of spectrograms obtained between April 2 

 and 8 a condensation at A 350 was a remarkable feature, 

 on .April 18 no indications of this condensation were present, 

 whilst on April 26 there was a strong condensation at A 346, 

 but nothing at all at A 350 ; later observations confirm this 

 interesting phenomenon. 



Visual observations of the spectrum of Nova Geminorum, 

 made by .Mr. H. D. Curtis on August 17 and 18 with 

 spectrograph No. i attached to the 36-inch refractor, showed 

 the three chief nebular lines well developed, H)3 faint, the 

 line at A 4959 rather stronger, and the line at A 5007, into 

 which the greater part of the Nova's light seemed to be 

 concentrated, very much more intense, whilst D and Ho 

 were not visible. The change of this star into one of the 

 nebular tvpe is apparently now complete (Lick Observatory 

 Bulletin, 'No. 48). 



OccuLTATioN OF A Star BY JupiTER. — A communication to 

 the Kiel Centralstelle, published in No. 3903 of the Astrono- 

 mische Nachrichten, announced that Mr. T. Banachiewicz, 

 of the Warsaw University, had observed an occultation of 

 the star B.D. — 6°.6i9i (mag. =6-5) by Jupiter at about 

 7h. lom. (Berlin M.T.) on .September 19. 



Several observers recorded their observations of this 

 phenomenon in No. 3906 of the Nachrichten, amongst 

 others Herr Kostinsky, of the Pulkowa Observatory, who 

 gave the times of immersion and emergence as 

 2oh. lom. 21s. ±is. and 2ih. 52m. 4s ±is. (Pulkowa S.T.) 

 respectively. 



In a letter to the October number of the Observatory, Mr. 

 Denning gives the details of his observations of the 

 phenomenon about half an hour after the probable reappear- 

 ance of the star, when it was situated at about 10* from 

 the S.S.E. limb of the planet. He states that the same 

 star will be about 20' south of Jupiter on December 29 at 

 approximately loh. G.M.T. 



Rotational Velocity of Venus. — Bulletin No. 3 of the 

 Lowell Observatory contains a description, by Mr. V. M. 

 Slipher, of some experiments made at that observatory in 

 order to determine, by the Deslandres spectrographic 

 method, whether Venus has a short rotational period or 

 not. 



The instrument used was the new Lowell spectrograph, 

 made by Brashear, which gives an angular dispersion of 

 46'-5 for one tenth-metre when set for the minimum devi- 



NO. 1774, VOL. 68] 



ation of A 4270. The spectrograph is so attached to the 

 adapter that it may be rotated about the optical axis in 

 order to obtain spectrograms with the slit in various relative" 

 positions; the plates used were fine-grain Seed's "23" 

 brand, and were exposed for about 8 minutes during the hour 

 immediately succeeding sunset, whilst the air currents were 

 most quiescent. For purposes of measurement an iron 

 spectrum was photographed on the same plate, and twelve 

 of the finest iron lines were used as fiducial lines. The 

 results obtained show very small probable errors, ax^ in- 

 dicate that Venus does not possess a short period of rota- 

 tion. A period of twenty-four hours would cause an inclin- 

 ation of the lines amounting to one-ihird of a degree, and 

 similar experiments performed on the planet Mars, and 

 published in Bulletin No. 4, show that a longer period than 

 this would be clearly indicated by the apparatus and method 

 used. 



THE STANDARDISATION OF ELECTRICAL 

 PRESSURES AND FREQUENCIES. 



WE have received a copy of the resolutions of the 

 Engineering Standards Committee with reference to 

 standard pressures for direct current and standard fre- 

 quencies. In view of the importance of the subject to the 

 electrical industry at large, the document is reprinted below 

 in full. 



Standard Direct Current Pressures and Standard 

 Frequencies. 



The standardisation of electrical pressures and frequencies 

 was the first portion of the important work entrusted to 

 the subcommittee on generators, motors and transformers 

 by the electrical plant committee. The subcommittee 

 consists of the following gentlemen :— 



Colonel R. E. Crompton, C.B. chairman. „,„<,„ 



Colonel H. C. Holden. R.A., Captain A. H. Dumaresq, 

 R.E., representing the War Office. 



Commander G. L. Sclater, R.N., Mr. L. J. Steele, re- 

 presenting the Admiralty. Anr«„tc 



Mr. Llewellyn Preece, representing the Crown Agents 



^^DnV^^T^Tazebrook, representing the National Physical 



^ m'^'^'^b'^^H. Antill, Mr. W. B. Esson, nominated by the 

 Electrical Engineers' Plant Manufacturers' Association. 



Mr. A. C. Eborall. 



Mr. S. Z. de Ferranti. 



Mr. Robert Hammond. 



Captain H. R. Sankey. 



Mr. C. H. Wordingham. 



Mr. Leslie S. Robertson, secretary. 



Mr. C. le Maistre, electrical assistant secretary. 



At an early stage in their deliberations, the subcom- 

 mittee decided that the most advantageous method ot 

 approaching this problem, beset as it is with so many 

 difficulties, would be from the point of v-iew of those most 

 affected, namely the users of lamps and of motors for power 

 purposed. It was therefore agreed that the standard 

 pressures to be suggested should be measured at the con- 

 sumers' terminals as settled by Act of i899- 



At the present time there exist many different pressures 

 declared by the various lighting and power authorities. In 

 view of the great desirability of obviating this unsatis- 

 factory state of affairs it was deemed advisable to suggest 

 the minimum number of standard pressures which would 

 best meet present commercial requirements and, at the 

 same time, utilise to the fullest extent the consumers exist- 

 ing appliances. -j .. * ♦u o,.k 



After careful consideration, it became evident to the sub- 

 committee that the direct current pressures of no, 220, 440, 

 and soo volts would best meet the requirements, because 

 carcases built for these standard pressures could be utilised 

 for pressures 10 per cent, above or below the suggested 

 standards, without any alteration whatever in the castings 

 or mechanical components, by merely altering the windings 

 and excitation. 



It is to be hoped that now these direct current pressures 

 have been fixed as standards by the committee, they will 

 in future be universally adopted by the engineers advising 



