ArcrsT 1, 1899.] 



KNOWLEDGE. 



189 



The phenomena of mixtm-e exhibited when one igneous 

 rock penetrates another have led Prof. Sollas* to question 

 the potency of differentiation ; and his general conclusions 

 may be supported in many other areas than the one 

 selected by him. Probably the French geologists are at 

 present most active in showing the extent to which an 

 igneous caldron may react on the surrounding rocks. 

 M. Barrois,f to take one excellent example, finds that the 

 granite of Menez-Belair, in Brittany, has eaten its way 

 along the strike of a series of tilted shales and sandstones, 

 but has penetrated the former to a far greater distance 

 than the latter. Bands of quartzite remain as ridges in 

 the granite area, and represent the undissolved layers of 

 the sandstone. This example of selective absorption 

 should go far to explain the position of many intrusive 

 igneous masses. Our caldrons do not merely occupy 

 hollows prepared for them by earth-movement ; they 

 extend at their surfaces by absorption, and the igneous 

 mass becomes increased in bulk, and at the same time 

 modified in composition. Provided that the absorption is 

 on an extensive scale, materials may be imported of such 

 differing character that a sort of average composition may 

 be reached. In such eases a uniform type of igneous reck 

 may be arrived at, not far different from those highly 

 siUceous masses that fill most of our soUdified caldrons at 

 the present day. Persistent absorption and melting imply 

 a return of the sedimentary materials towards the igneous 

 rocks from which they came. The cycle is, indeed, that 

 pictured by Hutton and the old geologists, though the 

 process is shortened by the direct refusion of the sediments, 

 instead of their progressive metamorphism. 



It may be observed, in conclusion, that M. Stanislas 

 Meunier,^ bold in his generation, is prepared to derive 

 all the water required for volcanic action from the 

 absorption of water-logged superficial rocks by the igneous 

 layers underneath them. Without making such large 

 demands, we may yet see in our familiar igneous rocks 

 the result of a series of mixtures, refusions, and interpene- 

 trations ; while down below, in still more mysterious 

 caldrons, he the purer magmas which rarely reach us 

 unalloyed. 



♦ 



NOTES ON COMETS AND METEORS. 



By W. F. Dexning, f.b.a.s. 



Swift's Comet (1899a). — This object is now exceedingly 

 faint, and in the early part of -August will be only one-fiftieth 

 as bright as it was at the time of its discovery early in March. 

 But its apparent brightness varies suddenly and unaccountably. 

 The following estimates by Holetschek. of Vienna, exhibits the 

 remarkable changes it underwent in June last. 



Jane 1 



o 



,, - 



„ .3 ... 



„ 4 ... 



„ 5 ... 



„ 6 ... 



„ 8 ... 



„ 9 ... 



Tempel's Comet (1873 XL). — This comet is now practically 

 invisible to observers in this country owing to its low position 

 in the sky. For the benefit of southern observers we give its 

 place on one moonless night in each of the next four months. 



•'"The EelatioQ of the Granite to the Gabbro of Bamavave," 

 Trans. R. I. Acad., Tol. XXX (1894), pp. 502—510. 



t " Le Bassiu du Menez-Belair," Annales de la Soe. Geol. du 

 Xord, Teme XXII. (1894), pp. 223, 231, 342, etc. 



: "La Geologie Experimentale " (1899), p. 266. 



E.A, Distance in Bright- 



Date, h. m. s. Dec. ^Umiions of Miles, ness. 



Aug. 4 ... 20 57 26 - 26° 14' 6" 3,5 3-59 



Sept. 5 ... 21 38 29 - 35° 59' 37" 47 1-89 



Oct. 3 ... 22 19 17 - 34° 7' 1» 67 O'SO 



Nov. 4 ... 23 8 29 - 26" 31' 7" 100 0-29 



Holmes's Comet should be favourably visible during the 

 first half of August, moving slowly to N.E., in the region 

 between the constellations of Aries and Perseus. The following 

 are its positions on three nights. 



R.A. 



Date, h. m. s. Dec. 



Aug. 4 ... 2 36 50 -i- 33° 4' 

 ,, 8 ... 2 41 43 -t- 34° 9' 

 „ 12 ... 2 46 24 + 35" 14 



CoDDlNGTOx's CoMET. — Mr. C. F. Merfield {Ast. Nach., 3577) 

 thinks that this object may just possibly continue to be visible 

 in August. Its position on August 3rd is R.A. oh. 11m. 34s., 

 Dec. + 0° 47', and on August 31st, E.A. 5h. 21m. Is., 

 Dec. -t- 1° 19'. Its distance from the earth on August 3rd 

 and 31st is four hundred and twenty-eight and four hundred 

 and sixteen milhons of miles respectively. The comet will 

 appear to be very nearly stationary during the month of 

 September. 



Barnard's Comet (1892 V.). — A sweeping ephemeris has 

 been computed by Coniel, but the re-detection of this faint 

 object must be undertaken by an observer having the use of a 

 large instrument such as that at the Lick or Terkes 

 observatory. 



Klinkeefues's Comet (1854 IV.). — The definitive orbit of 

 this comet has recently been determined by Drs. Buschbaum 

 and Steiner. About two hundred observations were obtained 

 between September Tith and Xovember 14th, 1854. The 

 computers find that the comet moved in an elliptical orbit with a 

 period of 1088'78 years, with a possible error of seventy years. 



Aerolite of March V2th. — The Bulletin de La Socit'tJ Asfrono- 

 miquf lie France (June, 1899) contains some interesting accounts 

 both of the flight of this luminous bolide and of the descent of 

 the sohd material comprising it. The object is described by 

 observers in Sweden, and others in Livonia and the X.W. parts 

 of Russia. At Borgo, in Finland, there took place something 

 like an earthquake, and it was there that the aeroUte fell on the 

 frozen sea surface, producing a hole nine metres in diameter. 

 The stone must have been a huge one, probably weighing one 

 thousand Idlogrammes. At several different places in Sweden 

 the colour of the fireball as it sped down the sky was described 

 as similar to that of an electric lamp, and its light surpassed 

 that of the full moon. Prof. Herschel has examined the various 

 accounts, and concludes that the radiant point was probably in 

 about 105° — 2i>°. The meteor nearly crossed the zenith at 

 Dorpat and Wesenberg, and after passing over the Gulf of 

 Finland, fell to earth at or near .Borgo, on the south coast of 

 Finland. It probably began over a point about fifty miles east 

 of Walk, in Livonia, and was eighty miles high when over 

 Wesenberg, its motion above the earth's surface being directly 

 towards X. by W. A Reuters telegram, dated Helsinfors, 

 May 26th, says : " The collected pieces of the aerolite which 

 fell at Burgo have been sent here and placed in the Geological 

 Museum. The largest piece is said to weigh two hundred and 

 six Russian pounds, while all the parts together weigh eight 

 hundred and fifty poimds." 



Meteoric Fireball of June 1st. — A very brilliant meteor was 

 observed at 9h. 20m. p.m. by observers at Kettering, Dewsbury, 

 Mannden, near Bishop Stortford, and other places. At Dews- 

 bury the lustre of the object was estimated as four times as 

 bright as Jupiter. The various observations are not, however, 

 sufficiently fuU to admit of the derivation of very precise 

 results, but it appears probable that the radiant point was 

 a])proximately in or near the zenith (at about 208° -i- 51°), and 

 that the meteor terminated its luminous flight at a height of 

 thirty miles above King's Lynn, in Norfolk. There is a well- 

 defined radiant near d Bootis (So. 164 of my General Catalogue 

 in Memoirs of the R.A.S., Vol. LIIL, p. 263) which conforms very 

 nearly in position and date with this fireball radiant. 



Thk Great Perseid Shower. — A favourable opportunity 

 will be presented this year for recording the progress of this 

 shower during the first half of August, as there will be very 

 little moonlight. It seems desirable to direct special attention 



