May 23, 1907J 



NA TURE 



OUR ASTRONOMICAL COLUMN. 



Comet 1907b. — From a note published in \o. 4175 

 (p. 366, May lo) of the Astronomische Nachrichten we 

 learn that the comet discovered by Mr. Mellish on April 14 

 had been previously seen by Mr. Grigg, of Thames, New 

 Zealand, on April 9. A set of elements computed by Mr. 

 Merfield from observations made on April 9, to, and 11 

 is given. 



In the same journal Dr. Ebell continues his ephemeris 

 for this object up to June 19, showing that the comet is 

 now appro.ximatelv half-way between 1 and B Ursje Majoris. 

 R.A.=gh. 2-6m., 5 = +5i° 18'. 



The Value of the Solar Parallax. — The discussion of 

 the Greenwich photographs of Eros, the results of which 

 were communicated to the Royal Astronomical Society 

 {Monthly Notices, vol. Ixvii, No. 6, p. 380) at its April 

 meeting, gave 8".Soo +o"oo44 as the value of the solar 

 parallax. This result was obtained from the measurement 

 of 151 plates taken with the .•\strographic 13-inch refractor 

 and 103 plates taken with the Thompson 26-inch refractor, 

 between October 14, 1900, and January 15, igoi, and 

 agrees very closely with the value, 8"-8o2 lo'-oos, pub- 

 lished by Sir David Gill in 1897. 



E.^RLY and Late Perseids. — In a paper recently com- 

 municated to the Royal Astronomical Society Mr. Den- 

 ning gives a list of the apparent paths of probable and 

 possible Perseids ob.served by him during the periods July 7 

 to 22 and August 17 to 25 inclusive, from 1S76 to the 

 present time. The observations suggest that true Perseids 

 may be looked for after the first week in July, but not 

 until July 19 does the stream become conspicuous enough 

 to enable a good radiant to be determined. Mr. Denning 

 asks other observers to supply data from which the radiant 

 during the earlier period might be determined with more 

 certainty ; at present there is reasonable doubt that the 

 shower commences so early as July 7. Similarly the ex- 

 tension of the date of apparition to August 25 is in ques- 

 tion, although Mr. Denning is sure that true Perseids 

 have been observed as late as August 20. 



A list of the radiants determined is also given, and the 

 author states that quite possibly the shower extends over 

 a period of fifty nights (Monthly Notices, vol. Ixvii., April, 

 p. 416). 



New Elements of Jupiter's Seventh Satellite. — From 

 twelve observations distributed evenly along the observed 

 arc passed over by Jupiter's seventh satellite during the 

 period January 3, 1905, to September 25, 1906, Dr. F. E. 

 Ross has computed a new set of elements for that satel- 

 lite. The principal perturbations have been included, and 

 the observations are represented by the elements with an 

 average error of only o'-4. The inclination of the satel- 

 lite's orbit, referred to the earth's equator for the epoch 

 January 00, 1905 (G.M.T.), is given as 25° 18' -6, whilst 

 referred to Jupiter's orbit the inclination is 27° s8'-3. The 

 period, according to these elements, is 26006 days. 



Observations secured by Prof. Max Wolf on December 

 22 and 23, 1906, and by Prof. Perrine on November 23, 

 are not consistent with these elements, the respective 

 residuals in R.A. being -fio'o and — 3'-3 (Astronomische 

 Nachrichten, No. 4175, p. 359)- 



The Computation of Cometary Orbits. — In Circular 128 

 of the Harvard College Observatory, Prof. E. C. Pickering 

 points out what needless duplication occurs in the com- 

 putation of cometary orbits. For comet 1907a three almost 

 identical sets of elements were communicated to the Har- 

 vard College Observatory, whilst others, giving similar 

 values, were published elsewhere. To obviate this waste 

 of energy Prof. Pickering suggests that these computations 

 should be carried out on some cooperative system, each 

 computer taking them in turn, and further suggests that 

 the labour thus saved might with advantage be expended 

 on the computation of orbits of minor planets, of which 

 objects so many are now being discovered regularly. 



AsTROGRAPHic Catalogue Work at the Perth Observ- 

 .4TORY (W.A.). — Although most of the Government Astron- 

 omer's report of the work performed at the Perth (W. 

 .■\ustralia) Observatory during the year 1905 is devoted to 



\0. 1960, VOL. 76] 



meteorological observation, Mr. Cooke has a few words 

 to say about the regrettable delay in the prosecution of 

 the .■\strographic Catalogue work undertaken by the West 

 Australian Government. 



The zone apportioned to the observatory was from 32° 

 to 40° south declination, and includes 1375 regions ; of 

 these 145 remained to be taken at the date of the report. 

 But the operations of measuring and reducing the plates 

 were not then commenced, and there is a grave possibility 

 that the plates may deteriorate sufficiently to render them 

 useless. The taking of long-exposure plates for photo- 

 mechanical reproduction was commenced, but was afterwards 

 stopped on account of the expense. Some 10,000 standard 

 stars have to be observed by means of the transit circle, 

 and Mr. Cooke suggests that " this will form the basic 

 work of the Perth Observatory, probably for centuries." 



The Total Solar Eclipse of August 30, 1905. — During 

 the total eclipse of August 30, 1905, Prof. Schwarzschild, 

 of the Gottingen Observatory, together with Prof. Runge, 

 made observations with a prismatic camera and a corona- 

 graph at Guelma, in Algeria. Part xxx. of the Asirono- 

 itiische Mitteiluugcti der konigj. Sternivarte zii Gottingen 

 contains a complete discussion of the results obtained. The 

 brightness and spectral photometry of the corona are first 

 dealt with at some length, and then the spectra obtained 

 are discussed, the origin, wave-length, intensity, and ex- 

 tension of each arc being given ; the region photographed 

 was from \ 4590 to X 3330, and the identifications include 

 the elements Vt, Zr, La, Ce, Nd, and Yb. 



THE ERUPTION OF KRAKATOA AND THE 

 PULSATION OF THE EARTH. 



'T'HE vibration of the earth may be caused by volcanic 

 eruptions and earthquakes, but it is doubtful if any 

 regular pulsation can be called forth by a sudden impulse 

 such as an earthquake or paroxysmal outbursts of 

 volcanoes. If any rhythmic pulsation ever comes into exist- 

 ence, it is most probably due to some exciting cause of 

 long duration, such as volcanoes of continuous activity 

 giving rise to occasional explosions, thus causing frequent 

 blows to the earth. The eruptions of Krakatoa afford an 

 example of such a method of excitation, and we have 

 reason to believe that there were pulsations with a period 

 of about 67m. 



The exact time of several minor explosions before the 

 great outburst at 10 a.m., August 27, 1883, is not well 

 known, but if we assume that the air was simultaneously 

 affected, the record of the gasometer at Batavia gives us 

 valuable information as to the sequence of the numerous 

 explosions beginning on August 26. The regular succession 

 of remarkable excursions in the indications of the 

 gasometer, reproduced in the Royal Society report on 

 Krakatoa eruption, is at once evident from the following 

 table :— 



Time interval 

 h. m. h. m. h. m. m. 



August 26 ... 5 2° P "1-1 6 49 = 3 24-5 X 2 = 68-2x6 

 ,, 27 ... o 9 a.m. t^ J t J 



' 5.=; 



2 38 



3 30 '< ■' 



4 41 „ I 

 4 S5 .. V, 



*5 43 



*6 57 ,. { 



825 „ 1, 



9 42 



*y '5 " u co= 60 



*II 15 .. i 



-3 20= 66-7x3 



,3 27= 69-0x3 



-3 22= 67-3x3 



The great explosions are marked with asterisks, while 

 the sign is doubled for the principal outburst. 



The whole interval = 67-2m. X 16. The mean interval of 

 successive explosions on .August 27, if those at ih. sjm. 

 and 2h. 38m. and at 4h. 41m. and 4h. 55m. are 

 counted as a single phenomenon, is also 67m. The re- 

 currence of several explosions at multiple intervals of 67m. 

 shows that they were not always irregular, but had a 



