OCTOBEB 2, 1899.] 



KNOWLEDGE 



237 



groundmass to a more resisting series, the latter having 

 been cut up into eyes some ten or twenty feet across. A 

 granite may, for instance, be intersected by a number 

 of basic dykes ; when metamorpbism sets in, that 

 is, when one whole region of the crust begins to slide 

 upon another, the granite flows again, tending to become 

 finer in grain as its constituents yield beneath the pres- 



FiQ. 1. — Microseojiic Section of Gneiss, witli Mylonitic Structure 

 in the more delicate bands. Lock Roag, Lewis, Outer Hebrides. 

 X 12. Drawn under polarised ligbt. 



sure. The tough dark -coloured dykes become broken 

 across, and huge lumps of them form eyes round which 

 the new gneiss moves. At the sams time, the margins of 

 these eyes become foliated ; augite breaks down into horn- 

 blende, streaked out by pressure into parallel layers. The 

 extreme stage of such a complex mass gives us a regional 

 gneiss of somewhat varying composition, here pale and 

 granitoid, here dark with amphibole and biotite. These 

 dark streaks, true foliation-layers in the gneiss, may be all 

 that remains to us of the series of dykes that once broke 

 through the granite. 



The mental reconstruction of a series such as this forms 

 one of the most fascinating problems for a geologist 

 in the open field. But we soon perceive that we must 

 abandon any idea of measuring the " eyes " of one rock 

 entangled in another by our pocket-rule, or even by our 

 surveying-tape. As Lapworth has shown us in the Scotch 

 Highlands, or as Suess has impressed upon us in de- 

 scribing his " horsts " of ancient rock, ■ whole districts may 

 be regarded as knots round which other districts have 

 been forced to break and flow. It is odd to look from our 

 microscopic section to the map of Europe, and to trace in 

 both the action of the great earth-mill. The waves of 

 contorted rock, pent up against some pre-existing crystal- 

 line core, and broken against it in all the complexity of 

 overfolds and regional faults — what are these but the 

 features that mark a gigantic foliation in the crust ? The 

 massive breccias that occur along the thrust-planes appear 

 as films of flowing mylonite. At one point, an "eye" provides 

 attractions for the Alpine climber ; at another, the yielding 

 ground-mass has been seized on by the peasant for his fields. ' 



* See KSOWLEDQE. Vol. XXI., p. 27. 



t Since the above was written, Dr. Maria il. Ogilvie (Xafure, 

 September 7th, 1899, p. 4-W), in the course of a remarkable paper on 

 •" Torsion-structure in the Alps," has called renewed attention to the 

 dragging and flow that accompany large movements in the crust. 



NOTES ON COMETS AND METEORS. 



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



Swift's Comet (1899 L) is now on the northern region of 

 Libra, but has probably passed out of reach of the most power- 

 ful telescope in existence. It was accurately observed for 

 position during about five months. 



Tempel's Comf.t (1873 II.) will be too far south for obser- 

 vation in this country. Ou October 25th the comet will be 

 situated about 1' north of the brilliant star Fomalhault in Piscis 

 Austi-alis. 



Holmes's Co.met (189'i III.) — This object is extremely 

 faint and only perceptible in large instruments. No observa- 

 tions, except the one announcing its discovery by Perrine, 

 appear to have been published in any of the scientific journals. 

 An ephemeris by Zwiers {Ast. Nach. 3582) gives its position on 

 October 3rd as R.A. 3h. 6m., Dec. 46° 56' north. 



No new comets have been discovered during the past few 

 mouths : in fact, there appears to be a temporary dearth of 

 conspicuous objects of this class. The dark autumnal sky will, 

 however, probably reveal one or two comets visible in small 

 instruments, and we await the definite announcement of their 

 presence from those vigUant observers engaged in comet seeking. 



The August Meteors (Perseids.) — Additional observa- 

 tions of this shower have now been received, and it appears 

 highly probable that the maximum occurred on the night of 

 August 11th, between 13h. and 14h.. but the number of meteors 

 counted proves the phenomenon to have been one of very 

 moderate intensity. Mr. Ivo F. H. C. Gregg, of Malvern, 

 found the horary rate for two observers as 70 between 

 13h. 30m. and Uh^ 30m. On about August 9th, 10th. and 11th, 

 a number of determinations of the place of the radiant point 

 were made by various observers, and it appeared to be in the 

 usual position. On earlier and later nights the centre of 

 divergence accorded well with the easterly motion which it 

 exhibited in previous vears. M. E. M. Antoniadi at Juvisy, 

 Mr. W. E. Besley at "Clapham, S.W., Mr. J. H Bridger at 

 Farnborough, and the writer at Bristol, noted this displacement 

 of the radiant or very decided indications of it, and the obser- 

 vations as a whole corroborate it in a very distinct manner. It 

 appears from a mean of the various positions that on August 1st 

 the radiant was in 32° + 54°, on August 10th in i4.\° + 67 J°, and 

 on August 14th in 50J°-i-57i°. One of the most brilliant of 

 the Perseids seen during the recent display appeared on 

 August lilth .at II In. 14m., and it was seen at Yeovil, Bridport, 

 Bristol, Cardiff, and Shifnal, Salo]). ' The meteor descended 

 from a height of 70 to 40 miles from above Cheltenham to 

 Bridgwater, and the length of its observed path was 54 miles. 



Firehdl of Auguat 2ith, Sh. 11m. — A splendid meteor was seen 

 by a large number of persons in various parts of England. At 

 places in Surrey the meteor passed through Perseus and dis- 

 appeared just under Capella. At Meltham, Yorks., Mr. C. L. 

 Brook estimated the meteor as one-sixth as bright as the moon, 

 and gave the path as frocn 352° + 13J° to 2°-l- 12i°. At Liver- 

 pool, Mr. C. jeft'eries noted that it passed from the centre of 

 Pegasus to between x Andromeda^ and 7 Pegasi, and thence into 

 Pisces. He describes it as like a spear with shaft and head 

 complete. A correspondent at Chester writes that he saw a 

 briUiaut meteor flying earthwards in N.E., and that shortly 

 afterwards he perceived a strong odour of sulphur. Two 

 observers near Leicester say they saw a ball of fire, which, 

 crossing the road in front of them, fell into an adjoining field. 

 It was quite low down, and did not appear more than one 

 hundred yards away from them. Another writer, at Weaste, 

 near Manchester, says that tbe meteor resembled a ball of fire 

 of most dazzling brilliancy, and from which long fangs of fire 

 were cast off during its transit. It disappeared suddenly when 

 apparently about two hundred yards from the earth. For 

 several days the newspapers contained a considerable number of 

 letters on this phenomenon. The real path of the meteor was 

 over the North Sea, and it appears to have fallen from a height 

 of seventy-seven to twenty-seven miles. The length of its 

 course was one hundi'ed and eighteen miles, and its radiant 

 point at 345° •<- 14°, close to the bright star a Pegasi. 



Fii-ehall of August 'llth, lOh. 13m. — This was an exceptionally 

 fine object, though it does not appear to have been so generally 

 observed as the one previously described. It a])peared in the 



