June 29, 191 1] 



NATURE 



595 



OVR ASTRONOMICAL COLUMN. 



Astronomical Occurkences for July: — 

 July 2. l8h. cm. The Sun in Apogee. 

 , 22h. cm. Jupiter stationary. 



3. I3h. ocn. Mercury in superior conjunction with the 



Sun. 



4. 2ih. 2im. Jupiter in conjunction with the Moon 



(Jupiter 0° 58' N.). 



7. 4h. om. Venus at greatest elongation, 45° 29' E. 



8. 2h. lom. Mercury in conjunction with Neptune 



(Mercury 2 19' N.)- 

 II. i8h. 19m. Uranus in conjunction with the Moon 



(Uranus 4'' 28' N.). 

 14. 9h. om. Neptune in conjunction wihthe Sun. 



19. 7h. 31m. Mars in conjunction with the Moon (Mars 



2° o' S.). 



20. iih. II m. Saturn in conjunction with the Moon 



(Saturn 3° 33' S.). 

 ,, i8h. om. Uranus at opposition to the Sun. 

 24. I4h. 42m. Neptune in conjunction with the Moon 



(Neptune 5° 29' S.). 

 26. 2oh. om. Mercury in conjunction with the Moon 



(Mercury 4° 6' S.). 



28. 9h. 1 8m. Venus in conjunction with the Moon 



(Venus 5° 47' S.). 



29. 2h. om. Mercury in conjunction with a Leonis 



(o Leonis 0° 9' S.). 

 ,, I3h. om. Jupiter at quadrature to the Sun. 



Rediscovery ok Wolf's Comet. — A telegram from the 

 Kiel Centralstelle announces the rediscovery of Wolf's 

 comet, by Prof. Ma.K Wolf, on June 19. The position of 

 the comet at i2h. 4-9m. (Ivonigstuhl M.T.) was 



R.A. = i8h. 46m. 16s., dec. = 13° 28' N., 



and its magnitude was 15. The position is about 15m. 

 west of C Aquila;. According to the continuation of the 

 ephemeris published by M. Kamensky in No. 4505 of the 

 Astronomische Nachrichten, the comet will move in a 

 north-westerly direction until July 15, when it will turn 

 south again. Its calculated magnitude for July, 

 September, and October is about 12-2, but from the 

 observation the actual magnitude is, at present, somewhat 

 fainter than the calculated. 



Mars. — Observations of Mars were commenced at the 

 Juvisy Observatory during the clear mornings of April, 

 and several well-known features were seen. The south 

 polar cap was seen to be surrounded by a dark belt, which 

 certainly had the appearance of an objective phenomenon. 

 Mare Sirenum was seen on April 24 as a diffuse spot 

 descending from the polar cap and fading gradually 

 towards the bright limb of the planet. The central region 

 to the north was seen to have the accustomed yellowish- 

 orange hue, and Titan was vaguely, but surely, seen. 

 These observations when the apparent diameter of the 

 planet was only 6" show that useful observations will be 

 possible considerably before the opposition, which takes 

 place on November 25. The account of these early 

 observations, in the June number of L' Astronomic, is illus- 

 trated by a drawing made by M. Qu^nisset at i6h. 20m. 

 on April 24. 



In La Nature (No. 1986, June 17) Dr. Mascart has an 

 interesting illustrated article, in which he_ discusses the 

 present state of the vexed question concerning the reality 

 of the Martian canals. The general result is that the 

 question is, as yet, by no means decided, but there is a 

 hope that the laboratory experiments being carried on by 

 M.M. Chapeau and Danjon may do something to elucidate 

 this difficult question further. 



The Problem of the Solar Motion.— Continuing the 

 discussion with Prof. Comstock concerning the proper 

 motions of faint stars, Dr. H. E. Lau publishes some 

 interesting results, accruing from the Copenhagen measures 

 of the Engelhardt stars, in No. 4502 of the Astronomische 

 Nachrichten. 



He finds that the mean proper motion of tenth-magnitude 

 stars is 3" per century at the most, and that it is smaller 

 in the Milkv Way than outside it. For the position of the 

 apex he obtains' A ==200°, D=-t-44°, and finds that the 

 proper motions of tenth-magnitude stars indicate a greater 



NO. 2174, VOL. 86] 



R.A. and declination than those of the brighter stars, but 

 the reality of this difference is still doubtful. A reduction 

 of the measures shows that the mean parallax of these 

 stars of the tenth magnitude lies between two and three 

 thousandths of a second of arc, and that the error of 

 Newcomb's precession constant does not exceed o-i" per 

 century. 



The Forms of Spiral \ebul.«. — The forms of spiral 

 nebulaj is a matter of moment in any investigation con- 

 cerning cosmical evolution, and any attempt to find some 

 general law which these early systems follow is therefore 

 of interest. Such a research is described by Herr \'on 

 K. V. (1. Pahlen in No. 4503 of the AstroiioDiisihc 

 Niiclinchteii. 



The author has studied photographs of many spiral 

 nebula; taken at the Lick and the Isaac Roberts Observa- 

 tories, and has attempted to find general equations to their 

 curves. .Among other nebulae, he has considered M. 33, 

 Trianguli, M. 74, Piscium, and M. 51, Canum VenatiVi. 

 In each case an Archimedian spiral was tried, but it was 

 found that a logarithmic spiral could be found which 

 better fitted the chief branches of the observed spirals. 

 The agreement of the calculated and observed curves is 

 shown by a number of graphs, and all are satisfactory 

 except the second branch of -M. 51, in which there appear 

 several discordances. The paper also discusses the prob- 

 able generation of such curves as are observed in these 

 objects. 



The Spectroscopic Binary o Persei. — o Persei is of 

 special interest as a spectroscopic binary because, as occurs 

 in one or two other cases, the calcium lines H and K do 

 not appear to participate in the general variations of the 

 radial velocity. In discussing the .Allegheny observations 

 of this star, Mr. F. C. Jordan pointed out that his value 

 for the velocity of the centre of the system did not agree 

 with the one obtained earlier by Vogel from the Potsdam 

 observations, and suggested the possibility of a systematic 

 personal error in the latter. 



To clear up this point, Dr. Ludendorff has made new 

 measures of the spectra, and finds that, although there is 

 a marked difference between Vogel 's measures and his 

 own, yet it remains probable that the difference between 

 Jordan and Vogel is to some extent real ; possibly a 

 third, as yet unconfirmed, body is included in the system. 

 As the spectrum of o Persei is diflficult to measure, 

 further investigations will have to be made to settle this 

 interesting point (Astronomische Nachrichten, No. 4500). 



THE COAL-DUST QUESTION IN THE UNITED 

 STATES AND IN AUSTRIA.' 



'T'HE first explosion that seems to have attracted atten- 

 ^ tion to coal dust in the United States occurred at 

 Pocahontas mine in 1884. Very little attention was paid 

 to the subject for some years afterwards, until explosions 

 began to occur in the western region " in shallow mines 

 in which firedamp had never been found before the 

 explosions, and was not found after them." .Although the 

 majority of these were not of a serious character, they 

 gave rise to much uneasiness ; but when what might be 

 called the black year of 1907, with a death-roll of " 1148 

 men killed by mine explosions," had run its course, un- 

 easiness gave way to consternation. In 1008 Congress 

 "made an appropriation" for the investigation of mine 

 explosions, which became available on July i ; the United 

 States G(>olc^ical Survey was entrusted with the work, 

 and an experimental station, which had, in the interim, 

 been erected at Pittsburg, was officially opened on 

 December 3 of the same year. 



Experiments which, in the bulletin before us, are 

 described as a preliminary series, have been made with 

 the object of determining " the quantity or density of the 

 finest size of coal dust necessary to propagate an 

 explosion." 



1 "The Exploslhilityof Coal Dust." By George S. Rice, with chapters by 

 .T. C. W. Frazer, Alex Larsen, Frank Haa», and Carl Scholz. United States 

 Oeological Survey, Bulletin 425. Pp. 186. (AVashington : Governmenl 

 Printing Offire, 1910.) 



Abstract of the Reporfi on the Austrian Coal-dust expK:rirnents condiicted 

 at the Ros.sitz experimental station 1908-1909 by k. k. Oberbergkomtnissar, 

 Pr. Cz.iplinski, and Werksdirektor Jicmsky. Pp. 36. (London : The Colliery 

 Guardian Company, Limited, 191 1.) 



