August 23, 1900] 



NATURIZ 



399 



meteors it is true, and of these it is hoped the real paths may be 

 computed ; but on the nights of August lo and 1 1 observers 

 were somewhat disappointed with the character of their results. 

 The effect of the full moon's influence in practically obliterating 

 a meteoric shower may not, however, have been given sufficient 

 weight. The best night appears to have been August 12, when 

 shooting stars were tolerably frequent considering the circum- 

 stances. 



But if moonlight presented an obstacle to success in the 

 second week of August, there was no such impediment early in 

 the month and during the last fortnight of July. The earlier 

 stages of the shower were therefore well observed. In fact, it 

 is questionable whether the Perseids have ever been more suc- 

 cessfully observed in the month of July. Among those who 

 participated in the observations were Prof. A. S. Herschel, 

 Messrs. J. R. Bridger, W. E. Besley, A. King, and many 

 others. At Cambridge a large number of meteors were re- 

 corded. The results show that the first Perseids were noticed 

 on about July 16, and gradually increased in numbers until the 

 date of maximum. The radiant showed the usual E.N.E. 

 motion in a most decided manner. 



At Bristol, between July 15-30, in 17 J hours of observation, 

 177 meteors were seen, including about 24 Aquarids (radiant 

 338"- 10') and 20 Perseids. But the only night on which a 

 sufficient number of Perseids were registered to indicate a good 

 radiant was July 30, when the position was at 3i°-f 54° from 10 

 paths. Several of the most prominent of the minor showers of the 

 epoch were observed, and their radiants accurately determined as 

 follows : — 



Other showers were indicated at 53° + 63°, 245° + 72°, 333° + 28°. 



Mr. W. E. Besley, at Clapham Common, London, registered 

 ,the paths of no meteors between July 14 and 24, and the great 

 majority of these were seen on the 23rd (30 meteors) and 24th 

 {51 meteors). His results are important, for on the former 

 date he found the radiant point of the Perseids at 23° + 51°, 

 and on the latter date at 25° +52^', from 5 and 7 meteors 

 respectively. 



Prof. A. S. Herschel, at Slough, during a series of short 

 watches between July 17 and August i, recorded 53 meteors, 

 including some very interesting early Perseids and several 

 Aquarids. The position of the latter radiant was placed at 

 339"- 12', from about 7 paths. 



Some of the meteors seen by Prof. Herschel were also" noted 

 by the writer at Bristol. The earliest Perseid of which duple 

 observations were secured appeared on July 19, at iih. 49m., 

 and it was a fine object, estimated to equal Jupiter by the Bristol 

 observer. The radiant from the combined paths was at 17^ + 50°, 

 and the heiglit of the meteor varied during its descent from 81 

 to 54 miles. Another Perseid was seen at Slough and Bristol 

 on July 23, I2h. 12m., of ist magnitude. Its radiant was at 

 24° + 52°, and height 84 to 55 miles. These radiants, together 

 with those determined by Mr. Besley on July 23 and 24, and 

 that by the writer at Bristol on July 30, agree very satisfactorily 

 with the ephemeris place of the radiant given by the writer in 

 Ast. Nach., 3546, and Memoirs R.A.S., vol. liii. p. 210. 

 ' Fairly bright Aquarids were recorded at Slough and Bristol 

 on July 28 and 30, with heights from 65 to 44 miles and 56 to 

 40 miles respectively. These meteors are usually lower in the 

 atmosphere than the Perseids, and move much slower. If we 

 take the radiant of the former shower in 1900 as 339°- li°, we 

 shall probably have a position which is certainly within l" of 

 probable error. 



On July 15, at loh. 13m., a Capricornid fireball was seen at 

 Bristol and four other places. It was a splendid object, about 

 three times brighter than Venus, in the northern part of England. 

 It fell from heights of 51 to 21 miles, along a path of 78 miles ; 

 velocity, 16 miles per second. 



On July 17, at 8h. 47m., a magnificent fireball appeared over 

 the northern part of England and Scotland. Though the sun 

 had not long set, the brilliancy of the meteor was described as 

 very dazzling, and the nucleus left a streak which remained 

 visible for three-quarters of an hour. The meteor was directed 

 from a radiant at 249" - 20° in Scorpio, and fell from a height 

 of 58 to 15 miles, along a path of about 175 miles. 



On July 24 another fireball appeared, and was rated at about 

 three times the brightness of Venus. It was seen at Bristol and 



KO 1608, VOL. 62I 



at several stations in the eastern counties. It fell from 68 to 27 

 miles, along a path of 103 miles ; velocity, 19 miles per second, 

 and was directed from a well-known July radiant at 280"- 15°. 



But the number of brilliant meteors which have recently 

 appeared is so large that the objects cannot be alluded to in 

 detail. Many ordinary shooting stars have also been doubly 

 observed, and these will be tabulated and published at a later 

 period. Among these there was an interesting 9 Perseid on 

 July 23, iih. 13m., with heights of 83 to 59 miles, and a radiant 

 at 30° + 47°, quite distinct from the true Perseids. 



On about August 10-12 the radiant of the Perseids was 

 found far east of its place in July. On August 12, Mr. King, 

 at Leicester, determined the position as 48^" + 58^ from 16 

 Perseids, and Mr. Besley derived it at 47" + 56.4° on the same 

 night from 4 meteors. On August 16 the writer at Bristol saw 

 5 Perseids from a radiant at 54" + 58°. 



Though the shower was partially obliterated by moonlight 

 just at the important time, it has this year furnished some in- 

 teresting materials for discussion as regards its earlier and later 

 stages. W. F. Denning. 



WHAT PRESSURE IS DANGEROUS ON 



ELECTRIC RAILWAYS WITH OVERHEAD 

 TROLLEY WIRES} 

 'X'HE following investigations were set on foot on account of 

 ■^ a dissension between the firm of Messrs. Brown, Boveri and 

 Co., Switzerland (Baden), and the- authorities regarding the 

 proper pressure for two different electric railways to be worked 

 by three-phase alternating current, namely, the lines Stansstad- 

 Engelberg and Fermatt-Garnergratt, which lines it was proposed 

 to work at a pressure of 750 volts. But this pressure being 

 regarded as dangerous, the authorities refused to allow one 

 exceeding 500 volts to be actually employed. 



In these circumstances the firm communicated with Prof. 

 H. F. Weber, of the Zurich Polytechnic, asking him to express 

 his opinion on this matter. In view, however, of his own want 

 of experience on this particular point. Prof. Weber commenced 

 a long series of investigations of the physiological effects of 

 the electric current on the human body, and he used himself as 

 the measuring instrument, thus exposing himself to great danger. 



The experiments were made with reference to the special 

 circumstances of the above railways, where the current was 

 supposed to be supplied through two overhead leads, the rails 

 being used as the third conductor of the three-phase system. 



Two series of experiments were made corresponding with the 

 cases — 



(«) A person seizes the two bare leads with both hands 

 simultaneously, or both of the leads fall on a bare part of the 

 human body. 



{b) A bare part of a person standing on the railway or on a 

 car comes into contact with one of the leads. 



The apparatus used in the case of experiments {a) consisted of 

 an iron ring wound with 630 turns of wire, through which was 

 sent an alternating current, the frequency of which was 50 per 

 second. The voltage between the first and the last turn was 

 kept at 210 volts. To every thirtieth turn was soldered a copper 

 wire of 10 cm. length, and 6 mm. diameter, and consequently 

 the pressure between the first and the second wire was 10 volts, 

 that between the first and third 20 volts, and so on, up to 

 210 volts. 



Prof. Weber tried these pressures successively on himself, 

 constantly holding with one hand the first wire and seizing 

 with the other hand each of the other wires in succession. The 

 experiments were made three times, his hands being each time 

 wetted to begin with, and afterwards being used dry. The 

 results of each of the three series so obtained were consistent 

 with one another. 



When experimenting with wet hands he obtained the follow- 

 ing results : — 



P.D. Effect. 



10 volts. Very feeble trembling of the muscles of the fingers ; 

 the current from hand to hand was measured 

 and found to be o'ooi ampere. 



20 volts. Very considerable trembling of the hands, wrists 

 and forearms ; the hands and the arms were 

 able to be moved freely, and the wires could be 



1 By William Rung, C.E. , of the firm of Brown, Boveri and Co., Switzer- 

 land. Translated from the Danish CiviUngeneer by F. Lehmann, M. F, 

 Danish C.E. 



