366 



NATURE 



\_Fcb. 1 8, 1886 



of a butterfly which the Mantis patiently waits for, perched on 

 the top of some conspicuous head of flowers. 



Simla, January 17 E. R. Johnson 



Fabry's Comet 



On the 6th inst., with a power of 38 on a 4^-inch refractor, 

 I observed that this comet had a distinct, though very faint, 

 tail, at a position-angle of about 85° ; length 13J'. The radius 

 of the coma was about 3'. I thought I could see the tail on the 

 1st inst., but was not quite sure of it then. The comet's spec- 

 trum strikes me as less distinct than is the case with most comets. 

 On the 1st inst. I could only see two bright lines (or bands) 

 certainly ; and the less refrangible of these was very faint. I 

 suspected a third band towards the more refrangible end of the 

 spectrum. T. W. Backhouse 



Sunderland, February 13 



Mist-Bow 

 On the Wiltshire Downs, near Marlborough, at about 40'clocl; 

 on February 10, I observed a white mist-bow, in position and 

 shape resembling the rainbow, but pure white, and the arc was 

 of considerable width throughout, estimated at 5°- 10°, altitude 

 of the sun iS°-20°, altitude of the summit of the bow 35°-45°. 

 The wind was slight, and there was a frost at the time, and a 

 thick deposit of rime on the trees, &c. Has this been observed 

 elsewhere or explained ? Is the phenomenon due to the super- 

 position of coloured bows, or to the polarisation of the semi- 

 crystallised vapour composing the fog? A, E. E. 



Movement of Telegraph- Wires 

 There can be no doubt that Mr. Mountford Deeley correctly 

 attributes the rogatory o.scillation of the wires during frost to the 

 air-current acting upon a " wing " of ice-spicules. I described 

 this plienomenon in Science Gossip, 1S74, p. 254, and explained 

 the cause of it in Nature, vol. xxiii. p. 338. 



Eirstal Hill, Leicester F. T. Mott 



liENR V BRADSHA W 



UNFORTUNATELY it far too often happens that 

 there seems to be an impassable gulf fixed between 

 the man of letters and the man of science, which hinders 

 the one not only from partaking in, but even from appre- 

 ciating, the ideas, the objects, and the methods of the 

 other. There is no need, especially here, to impute blame 

 to either ; but when a man of letters is found wdio, 

 modestly making not the least pretension to scientific 

 knowledge, yet sympathises deeply with the man of 

 science, some acknowledgment of the fact seems to be 

 due. Such an instance there was in Mr. Henry Brad- 

 shaw, Senior Fellow of King's College, and Librarian of the 

 University, whose sudden removal Cambridge is now- 

 mourning. Of his literary ability, his bibliographical 

 accuracy, bis mastery of one iinportant period of English 

 poetry, and his knowledge of early printed books, this is 

 not the place to speak. Justice to those qualities doubt- 

 less is being, or will in due time be, rendered by other 

 writers, better fitted to pronounce an opinion upon them. 

 But here may be appropriately recorded the enthusiasm 

 — for no other word will suit — with which he at all times 

 entered into and aided inquiries, investigations, and re- 

 searches that most men in his position would have con- 

 sidered to lie entirely outside of their own, and as such 

 to be without any dereliction of duty disregarded. His 

 time, his energy, and his varied attainments were always 

 at the disposal of any member of the L'niversity, 

 whose servant, in the highest sense of the word, he 

 rejoiced to be. But there was no need for any 

 one to be a member of the University to obtain 

 his help. Accessible at all times to all who sought him, 

 the asking of a simple question was a sufficient introduc- 

 tion, and whether that introduction was only the prelude 



to an acquaintanceship which might speedily ripen into 

 a friendship depended far more on the person who asked 

 it than on himself By the younger members of the 

 University to whom he was known, and the number of 

 them was vast, he was regarded with feelings of affection, 

 that it would seem almost exaggeration to describe, and 

 his influence over them, always tending towards the 

 highest ends, was proportionately great. But here it is 

 more fitting to dwell upon the active sympathy he showed 

 with students of biology. His great intimacy with the 

 late Mr. G. R. Crotch had led him to take an extreine 

 interest in the literature of systematic zoology, and par- 

 ticularly in the precision which is required of those who 

 pursue the branch of it relating to the Coleoptera, not 

 tliat Mr. Bradshaw must be supposed to have had any 

 knowledge of the subject. It was simply the method of 

 accurate work w'hich excited his admiration, and that 

 method, he has more than once told the present writer, 

 had largely influenced his own bibliographical investiga- 

 tions, the high value set upon which must be told by 

 those whom they concern. Never taking offence, wholly 

 free from pride, always ready to put the best construction 

 on every man's conduct, catholic in all his feelings, Mr. 

 Bradshaw passed away in his College rooms, apparently 

 without any suffering, on the night of the loth or 

 morning of the nth of this month — an end to be envied 

 by most men. A. N. 



THE COAL-DUST QUESTION 

 T N the last paragraph of my letter to NATURE (Dec. 31, 

 ■'■ p. 197), I stated that those who, having investigated 

 the question of the influence of coal-dust in colliery explo- 

 sions, had come to the conclusion that coal-dust is not, as 

 a rule, the principal agent in an explosion occurring in a dry 

 and dusty mine, appear to have omitted to take one im- 

 portant element of the case into consideration ; and in 

 saying so I implied that, if they had not made this omis- 

 sion, their conclusions in this respect would probably have 

 been more in accordance with my ow-n. 



All the important experiments with coal-dust on a large 

 scale have been made in wooden boxes or galleries of 

 greater or less length, open at one end and closed at 

 the other. The ignition or explosion has usually been 

 begun at or near the closed end, and been propagated 

 towards the open end, driving part of the contents of the 

 gallery out into the air in front of it. 



Certain conclusions in regard to colliery explosions, 

 have been drawn from the results obtained on this small 

 scale which appear to ignore the fact that the conditions 

 here prevailing are far less favourable to the propagation 

 of the coal-dust flame thin those which obtain in a mine 

 at the instant an explosion is sweeping through it. For, it 

 is obvious that in the former case the air is practically at 

 lonstant pressure while the explosion lasts, whereas in the 

 latter case it is practically at constant volume during the 

 same period. But as the amount of heat required to raise 

 the mixture of air and coal-dust to the temperature of 

 ignition in the first case is greater than that required to 

 effect the same result in the second case in the ratio of 

 r4i to I, it follows that an explosion having been once 

 begun in either case will be propagated much more rapidly 

 and surely in the mine than in the apparatus. Thus it is 

 that a kind of coal-dust which produces comparatively 

 feeble results in the apparatus may give rise to very 

 disastrous consequences in the mine. 



An illustration of this difference of behaviour under the 

 two sets of conditions has been furnished by the dust of 

 Camphausen Colliery in Germany. When subjected to 

 the experimental test in the large apparatus at Neun- 

 kirchen, ah'eady described in these pages, it was found 

 to be far down the list in point of relative danger, and 

 was pronounced to be, like most of the other dusts in the 

 same list above and below it, of a comparatively harmless 



