[20 



NATURE 



[November ig, 1914 



Series Lines in Spark Spectra.— In the issue of 

 this journal for April 9 of the present year (vol. xciii., 

 p. 145) a summar}' was given of the Bakerian lecture 

 delivered by Prof. Fowler on April 2 on series lines in 

 spark spectra. Attention is directed to the fact that 

 this lecture is now published in the Philisophical 

 Transactions of the Royal Society (Series A, vol. ccxiv., 

 pp. 225-66), and is accompanied by some excellent 

 reproductions from photographs of the spectrum of 

 the magnesium arc in vacuo, the various series of arc 

 and enhanced lines being clearly indicated. 



A Brilliant Fireball. — Mr. W. F. Denning writes : 

 "On November 11, at 11. 13 p.m., a magnificent 

 meteor was seen from near Purley, Surrey, Stow- 

 market, Hornsey, and other places. It looked like an 

 unusually large ball from a Roman candle firework, 

 and moved very slowly in the north-east sky, occupy- 

 ing about 6 sec. in an extended course. It was not 

 a Leonid, but apparently from a radiant near a Lyrae 

 in the north-west. The meteor illumined the sky 

 vividly for several seconds, and was evidentlv rather 

 near the earth's surface. From a preliminary dis- 

 cussion of the few descriptions already to hand it 

 appears that the object fell from a height of fift}- to 

 thirty-two miles, and its velocity was about eleven 

 miles a second. There is no known shower near Vega 

 at the middle of November, but certain large meteors 

 appear to be isolated. Some of the observers sup- 

 posed it to have been one of the regular November 

 meteors, but its direction was different and its speed 

 altogether too slow for it to have been a Leonid." 



Measured Par.allaxes Summarised. — A reprint 

 from the Astronomische Nachrichten, No. 4754, has 

 been received, and it contains a communication on 

 measured parallaxes summarised by Mr. O. R. 

 \\'alkey. The author states that in view of the 

 inherent uncertainty of all measured parallaxes, it 

 does not seem profitable to enter into a detailed dis- 

 cussion of the individual results, but instead the 

 results are summarised in a series of tables of dis- 

 tance and consequent luminosities and cross-motions 

 speeds according to the spectral type. The tables 

 given represent 521 stellar systems, not counting 

 the sun. The first three tables do not include the 

 H3'ades group, which consists mainly of first-type 

 stars ; these are dealt with in a fourth table accord- 

 ing to their component spectral classes. The investiga- 

 tion is one that is the result of a large amount of 

 labour, and the essence of the work lies in the 

 tables, which will no doubt be carefully scrutinised 

 by those to whom the subject is of special interest. 



Report of the Paris Observatory ior 19 13. — 

 Like all other large observatories situated in or near 

 towns, the work of the Paris Observatory is being 

 severely handicapped by the presence of disadvan- 

 tageous observing conditions such as smoke, night 

 glare, etc. The report for the year 1913 gives a 

 good idea of the great number of branches of work 

 undertaken, but in the different summaries of the 

 recent progress there is an underlying tone of regret 

 that much cannot be done and much that is done 

 is not as satisfactory as it might have been owing to 

 the present observing conditions. Monsieur Baillaud, 

 the director, opens his report with a reference to the 

 deplorable conditions of the actual situation and to 

 the indispensability of the creation of a branch estab- 

 lishment which he advocated two years ago. With 

 regard to the meridian work, the north and south 

 horizons have been shut out by seven-storev buildings, 

 and he points out how the work of the equatorials 

 is restricted by the haze and fog in the lower strata 

 of the atmosphere of Paris. Comet Delavan was 

 estimated as of the eleventh magnitude at Besan^on. 



NO. 2351, VOL. 94] 



Bordeaux, and Lyon, while at Paris it appeared of 

 magnitude 13. Regular photometric work, so im- 

 portant for the undertaking of the Carte du Ciel, is 

 described as impossible, and in the astrophvsical 

 department the quality of the stellar images pro- 

 jected on the slit exercises unfortunately a very greai 

 influence on the determinations of radial velocity. 

 Numerous other .•■eferences to other branches of work 

 effected are given, making a clear case for the 

 necessity for an out-station. For the present, no 

 steps can be taken, but it is hoped that in the near 

 future Monsieur Baillaud 's appeal will be considered 

 and carried out. The annual report takes the same 

 form as in previous years, and the work of the 

 several departments during the past year is describt d 

 in the various sections. 



THE FUNCTION OF THE EARTH IN 

 RADIO-TELEGRAPHY. 



A lecture; on the above subject was delivered 

 ■^"^ on Friday evening, November 13, by Dr. J. A. 



Fleming, to the members of the Wireless Society of 

 London, at the Institution of Electrical Engineers. 

 Dr. Fleming said that the present period of enforced 

 inactivity for all loyal radio-telegraphists, except those 

 engaged at the seat of war, offered an opportunity to 

 re-consider some of the purely scientific questions in- 

 volved in the art. He proposed therefore to discuss 

 the function of the earth in radio-telegraph)^ Apart 

 from the disputed question whether the aerial wires 

 should preferably be earthed at the base or connected 

 to an insulated balancing capacity, it was well known 

 that the nature of the soil or surface between the 

 transmitting and receiving stations had a great effect 

 on the signal strength. This effect depended much 

 upon the wave-length. Thus Dr. L. W. Austin had 

 shown that the ground to the north and north-east 

 of Newport, Rhode Island, U.S.A., exercised a 

 powerful absorption on radio-telegraphic waves of 

 about 1000 metres wave-length. Experiments made 

 between Brant Rock wireless station and a U.S. 

 cruiser Birmingham, lying at Newport, showed that 

 whereas electric waves of 3750 metres wave-length 

 suffered little or no absorption in travelling over the 

 45 miles other than that due to the normal space 

 decrease of energy, waves 1000 metres in length lost 

 95 per cent, of their signalling energy in passing over 

 the same district. 



Dr. Fleming first gave a brief mathematical dis- 

 cussion showing the manner in which the gradual 

 penetration of an alternating current into a conductor 

 can be explained. It is well known that high frequency 

 electric currents are confined to a thin skin or layer 

 of the surface of inetallic wires. In the case of 

 copper this skin has a thickness of about 0-25 mm. 

 for currents of a frequency of one million. In the 

 case of iron the skin for the same frequency is about 

 002 mm. 



An elegant experiment was shown by Dr. Fleming 

 with his cymometer to illustrate this surface flow of 

 high-frequenc\' currents. An oscillation circuit was 

 arranged in which high-frequency currents were 

 generated, and these were detected by placing along- 

 side a cymometer having a Neon vacuum tube as a 

 detector of secondarv oscillations in its circuit. In the 

 primary oscillation circuit were inserted successively 

 small spirals of copper, brass, iron, and galvanised 

 iron ; all having the same size and same number of 

 turns. The oscillations in the cymometer circuit were 

 indicated by the brilliant glow of the Neon tube. When 

 the iron spiral was inserted the Neon tube did not 

 glow, because of the damping of the oscillations 

 caused by the energy absorbed to magnetise the iron. 



