September 30, 1915J 



NATURE 



123 



OVR ASTRONOMICAL COLUMN. 



A New Comet. — A Copenhagen telegram reports 

 the discovery of another comet by Mr. J. E. Mellish. 

 In addition to the signatures of Profs. Pickering and 

 Stromgren, the message bears the name of Aitken, 

 and the position of the: object appears to Jiave been 

 measured at Lick. Thus there are sufficient grounds 

 for presuming an authentic comet has been detected, 

 although the communcation contains no information 

 regarding the movement (or magnitude) of the object. 

 Its position on September 19 i6h. 19m. 2s., Lick 

 time, was R.A. loh. 37m. 54s., dec. 26° 13' 17", i.e. 

 between 40 and 41 Leo Minoris. 



With reference to the note in this column last week, 

 readers who have not the opportunity of consulting 

 Dreyer's Catalogue may be interested to learn that 

 N.G.C. 2261 is therein stated to show a cometic 

 nucleus. 



The Variation of Latitude,— Two papers in 

 recent numbers of the Astronomische Nachrichten 

 bear on this- subject. In No. 481 1 Dr. E. Przybyllok 

 publishes results of an investigation into the effect on 

 latitude determinations of that part of the atmospheric 

 refraction due to the air inside the observatory differ- 

 ing in temperature from the external. It is found 

 that measures of the altitude of the pole show a daily 

 : fluctuation in magnitude varying directly with the 

 .altitude of the sun. Among the numerous citations 

 -^-there seems to be no reference to the work of Mr. 

 'S. Shinjo — one significant item concerns a systematic 

 •difference amounting to 011" found between visual 

 and photographic determinations caused by the heating 

 effect of a small dark-room lamp fixed to the south 

 of the photographic zenith sector. 



In No. 4812 von B. Wanaeh discusses the Kimura 

 term "z." Dr. de Sitter's view is adopted that the 

 greater part of this term is due to the method of 

 reduction. Refraction anomalies are considered to be 

 a sufficient cause for the remaining part. The "z" 

 term having been hypothesised out of existence, the 

 attempt is made to modify the group corrections as 

 obtained by the " Kettenmethode," so that in the mean 

 ."z" vanishes for all stations and years. To this end 

 a modified "z" is taken as a negative declination 

 correction, and new values are derived for the group 

 corrections for the six northern international stations. 

 The differences between successive groups show an 

 annual oscillation having a maximum in spring and 

 'a minimum in autumn, whilst the amplitudes for the 

 -three Continental stations markedly exceed those at 

 -the "maritime" situations, thus indicating the prob- 



■ ability that variations of zenith refraction of meteoro- 

 . logical origin are operative. 



Stellar Proper Motions determined Stereo- 

 scopiCALLY. — Quite recently M. Comas Sola, of the 

 Barcelona Observatory, recorded some qualitative 



■ observations of stellar cross-motions obtained by 

 stereoscopic comparison of stellar photograms (this; 

 col., August 26). According to the Asironomische 

 Nachrichten (No. 481 1) it now, appears that Prof.; 

 Max Wolf has employed the stereoscope niost success- 

 fully in quantitative determinations. Results are 

 given of measures of the proper motions of eight 

 stars in the neighbourhood of a- Leonis made on plates 

 secured with the i6-in. Bruge telescope at an interval 

 of 12- 108. years, one of the plates having been taken 

 in 1903, the other in the early part of the present year. 

 ■The stars measured ranget from .7o-i2-5ni.' magni- 

 tude, and.the yea,rly motion? vary from 0-31" to^ i-i8". 

 Some of the stars' have been measured previously, 

 e.g. the pair 83 Leonis by Kobold among others, who 

 found the annual motion of .0-77", '^wTiilst the new 

 method gives 0-74" for the same quantity. 



NO. 2396, VOL. 96] 



Rotation Period of Neptune.— Mr. Maxwell Hall 

 has published (Monthly Notices R.A.S., vol. Ixxv., 

 No. 8) the results of photometric observations of this 

 planet made during its recent opposition ; thirty-five 

 measures of magnitude were obtained during the 

 f>eriod February 26 and May 10 of the present year. 

 The magnitude ranged from 687 to 776, and the 

 period which best fitted the measures was 7h. som. 

 68s. Similar observations made during November, 

 1883, gave a period of 7h. 55m. Greater continuity 

 in the series of observations is necessary, and the 

 co-operation of observers well distributed in longitude 

 is therefore invited. 



The Internal Constitution of the Earth. — Mr. 

 Harold Jeffreys, who has recently published several 

 important theoretical investigations on the physics of 

 the earth and moon (Mem. R.A.S., vol. Ix., part vi., 

 and Proc. R.A.S., vol. Ixxv., No. 8, pp. 648-658), 

 contributes a very useful article to the current number 

 of the Observatory on the mechanical properties of 

 the earth. A good idea is given of the manner in 

 which a number of apparently widely differing lines 

 of investigation have in reality converged in adding 

 to our information— albeit at times in a somewhat 

 conflicting fashion — regarding the state of the earth's 

 interior. 



Photometric Observations of 8 Cephei. — During 

 the period June lo-September 26, 1914, Dr. Giuilo 

 Bemporad and Dr. V. Fontana collaborated in making 

 a fairly numerous series of photometric measures -.f 

 the light of this star. Dr. Bemporad 's results appear 

 in the Mem. Spett. Ital., June, 1915. The mean light 

 curve shows a secondary maximum, and at a later 

 phase an inflection. A further analysis of the data 

 was made with special reference to the secondary 

 oscillations. 



The Evolution of the Stars and the Formation 

 of the Earth. — The second course of lectures on the 

 William Ellery Hale foundation was given at the 

 meeting of the National Academy of Science at 

 Chicago last December by Dr. W. W. Campbell 

 under the above title. These lectures are now being 

 published in The Popular Science Monthly, begin- 

 ning in the September number. 



THE ETNEAN EARTHQUAKES OF MAY, 

 1914. 



THE term volcanic earthquakes has for long been 

 applied to all earthquakes originating within 

 the bounds of active or dormant volcanoes. Such 

 earthquakes are usually distinguished from ordinary 

 tectonic earthquakes by their small disturbed areas, 

 the great intensity of the shocks near the centres of 

 those areas, the brevity and abruptness of the shocks, 

 and the comparative absence of fore-shocks and after- 

 shocks. While the countless tremors which precede 

 and accompany volcanic explosions are no doubt the 

 effects of such explosions, it has been assumed, per- 

 haps rather hastily, that all volcanic earthquakes are 

 as intimately connected with .the volcanic operation?. 

 Several recent investigations (see Nature, vol. xcii., 

 pp. 716-7; vol. xcv., p. 215) have, however, shown that 

 many volcanic earthquakes are of a tectonic or semi- 

 tectonic character, and that both eartliquakes and 

 eruptions are in all probability effects of the same 

 cause or causes. 



The more important Etnean earthquakes evidently 

 belong to this category. • They originate beneath the 

 volcano — in recent cases, below Its eiastern flank — and 

 they are closely associated in point of time with ^ex- 

 plosions or periods of increased activitv of the volcano. 

 Moreover, their seismic foci are at a slight depth. On 



