226 



NA TURE 



[ytily 23, 1874 



Her from the firedamp, but enable him to apply it to 

 use, and destroy it at the same time that it gave him a 

 useful light (Phil. Trans. 1S16, pp. 23 and 24). Fortu- 

 nately the ventilation of mines is now better understood 

 than it was in the days of Davy, and the quantities of 

 nir employed are usually very much greater. It is cer- 

 tain, however, that in some mines of the present day the 

 ventilation could be doubled or trebled with advantage ; 

 and since this is merely a matter of expense it may be 

 asked why it is not done, when it would ensure com- 

 parative immunity from danger .' On the other hand it is 

 now almost universally admitted to be highly dangerous 

 to continue work in an explosive atmosphere, so that 

 safety-lamps should be used only as a precaution against 

 possible outbursts of gas or when work is carried on in 

 the neighbourhood of gas that cannot be easily dislodged ; 

 it is evident, therefore, prititA facie, that lamps constructed 

 on the principle of the " safety-lantern," such as the 

 Stephenson, Mueseier, &c., which are extinguished in an 

 explosive mixture, arc far safer than lamps like the Davy 

 or Clanny, which continue to burn under the same cir- 

 cumstances, and are then liable, at any instant, to have 

 the flame driven through the wire gauze and communi- 

 cated to the external explosive atmosphere. 



THE COMET 



[The following letter appeared in last Thursday's Times, 

 from the columns of which journal it is reproduced, 

 with a few verbal alterations.] 



T WAS enabled on Sunday night (12th inst.), by Mr. 

 J- Newall's kindness, to spend several hours in examin- 

 ing the beautiful comet which is now visiting us, by means 

 of his monster telescope — a refractor of 25 in. aperture, 

 which may safely be pronounced the finest telescope in 

 the world, or, at all events, in the Old World. 



The view of the comet which 1 obtained utterly exceeded 

 my expectations, although I confess they were by no 

 means moderate ; and as some of the points suggested by 

 the observations are, 1 think, new, and throw light upon 

 many recorded facts, I beg a small portion of space in 

 the Tillies to refer to them, as it is important that ob- 

 servers should have their attention called to them before 

 the comet leaves us. 



I will first deal with the telescopic view of the comet. 

 Perhaps 1 can give the best idea of the appearance of the 

 bright head in IVIr. Newall's telescope, with a low power, 

 by asking the reader to imagine a lady's fan opened out 

 (160") until each side is almost a prolongation of the other. 

 An object resembling this is the first thing that strikes the 

 eye, and the nucleus, marvellously small and definite, is 

 situated a little to the left of the pin of the fan — not 

 exactly, that is, at the point held in the hand. The 

 nucleus is, of course, brigfiter than the fan. 



Now, if this comet, outside the circular outline of the 

 fan, offered indications of other similar concentric circular 

 outlines, astronomers would have recognised in it a great 

 sinularity to Donati's beautiful comet of ICS5S with its 

 "concentric envelopes." But it does not do so. The en- 

 velopes are there undoubtedly, but, instead of being con- 

 centric, they are excentric, and this is the point to which 

 1 am anxious to draw attention, and, at the risk of being 

 tedious, I must endeavour to give an idea of the appear- 

 ance presented by these excentric envelopes. Still re- 

 ferring to the fan, imagine a circle to be struck from the 

 left-hand corner with the right-hand corner as a centre, 

 and make the arc a little longer than the arc of the fan. 

 Do the same with the right-hand corner. Then with a 

 gentle curve connect the end of each arc with a point in 

 the arc of the fan half-way between the centre and the 

 nearest corner. If these complicated operations have 

 been properly performed the reader will have superadded 

 to the fan two ear-like things, one on each side. Such 



" ears," as we may for convenience call them, are to be 

 observed in the comet, and they at times are but little 

 dimmer than the fan. 



At first it looked as if these ears were the parts of the head 

 furthest from the nucleus along the comet's axis, but 

 careful scrutiny revealed, still in advance, a cloudy mass, 

 the outer surface of which was regularly curved, convex 

 side outwards, while the contour of the inner surface 

 exactly fitted the outer outline of the ears and the inter- 

 vening depression. This mass is at times so faint as to 

 be invisible, but at other times it is brighter than all the 

 other details of the comet which remain to be described, 

 now that I have sketched the groundwork. These details 

 consist of prolongations of all the curves I have referred 

 to backwards into the tail. 



Thus, behind the bright nucleus is a region of dark- 

 ness (a black fan with its pin near the pin of the other 

 pendant from it, and opened out 45° or 60' only will re- 

 present this), the left-hand boundary of which is a con- 

 tinuation of the lower curve of the right ear. The right- 

 hand boundary is similarly a continuation of the lower 

 curve of the left ear. Indeed, I may say generally — not 

 to enter into too minute description in this place — that 

 all the boundaries of the several different shells which 

 show themselves, not in the head in front of the fan, but 

 in the root of the tail behind the nucleus, are continuous 

 in this way — the boundary of an interior shell on one 

 side of the axis bends over in the head to form the 

 boundary of an exterior shell on the other side of the 

 axis. 



At last, then, I have finished my poor and, I fear, tire- 

 some description of the magnificent and truly wonderful 

 sight presented to me as it was observed, on the whole, 

 during some hours' close scrutiny under e.xceptional at- 

 mospheric conditions. 



I next draw attention to the kind of change observed. 

 To spealv in the most general terms, any great change in 

 one "ear " was counterbalanced by a change of an opposite 

 character in the other ; so that when one ear thinned or 

 elongated, the other widened ; when one was dim, the 

 other was bright ; when one was more " pricked " than 

 usual, the other at times appeared to lie more along the 

 curve of the fan and to form part of it. Another kind of 

 change was in the fan itself, especially in the regularity of 

 ils curved outline and in the manner in which the straight 

 sides of it were obliterated altogether by light, as it were, 

 streaming down into the tail. 



The only constant feature in the comet was the exqui- 

 sitely soft darkness of the region extending for some little 

 distance behind the nucleus. Further behind, where the 

 envelopes of the tail were less marked, the delicate veil 

 which was over even the darkest portion became less 

 delicate, and all the features were merged into a mere 

 luminous haze. Here all structure, if it existed, was non- 

 recognisable, in striking contrast with the region round 

 and immediately behind the fiin. 



Next it has to be borne in mind that the telescopic 

 object is after all only a section, from which the true 

 figure has to be built up, and it is when this is attempted 

 that the unique character of this comet becomes apparent. 

 There are no jets, there are no concentric envelopes ; but, 

 as I have said, in place of the latter, excentric envelopes 

 indicated by the ears and their strange backward curv- 

 ings, and possibly also by the fan itself.* 



I prefer rather to lay the facts before observers than to 

 state the conclusions to be derived from them, but I can- 

 not help remarking that, supposing the comet to be a 

 meteor- whirl, the greatest brilliancy is observa'ole where 

 the whirls cut or appear to cut each other ; where wc 

 should have the greatest number of particles, of whatever 

 nature they may be, in the line of sight ; and not only so, 



* Ry describing three p.irabolas on a card and spinning the card rapidly 

 round a line not coincident with their common .ivis, I have been able to 

 reproduce roughly the appearances figured last week and described above. 

 —J. N L. 



