224 



NATURE 



\Jttly 7, 1 88 1 



M. Bigourdan says he first perceived the comet on 

 June 22 at I3h. 30m. The following elements are deduced 

 from the observation at Kiel (where the comet was seen 

 two hours earlier than at Paris) on June 22, and the two 

 following at Paris : — 



June 24 ... 9 SI 26'0 

 26 ... 10 46 5'8 



5 38 21-84 - +49 S 3><5 

 5 47 22-66 ... +56 so 2-4 

 Perihelion passage, 1S81, June 16-52806 



B — 265 22 59 1 



a = 270 57 51 I Mean equin. iSSi'o. 



i = 63 26 57 ) 



Repi-esentation of mean observation 



In longitude (o - C) cos /3 = -7"-7 



In latitude o - C = -4"-3 



The last elements obtained by Bessel for the great 

 comet of 1807 are as follows ; — 



Perihelion passage, 1S07, .September lS-74537 mean Paris time. 



o =: 270 54 42 J 



9, = 266 47 II > Mean equin. 1807. 

 i = 63 10 28 ) 

 log. (/ = 1-810,3158 

 ■• = 0-995-4878 



With regard to the physical constitution of the comet, 

 M. Wolf points out that while Coggia's comet (1874) — the 

 only large comet visible on the horizon of Paris since 

 spectrum analysis came into use — was at first telescopic, 

 developed rapidly, and disappeared at the most interesting 

 stage, the present comet comes to us already very much 

 developed after its passage through perihelion. The 

 transformations of the nucleus and its envelopes are 

 extremely rapid (as the drawings show). In the large 

 telescope the segmentation of the head, which Bond 

 found in Donati's comet, was distinctly visible on June 

 24 ; the smallest instruments did not show it. 



" The new coinet represents, then, the second period of 

 development of one of these curious stars, of which we 

 have the first only in Coggia's comet. Its study enables 

 us to follow the transformations of the envelopes, and to 

 complete what information the comet of 1874 supplied. 



" From the standpoint of spectrum analysis we may 

 now correct a premature conclusion which might be 

 deduced from our observations of Coggia's comet in 1874. 

 That comet, from IVIay 19, presented the continuous and 

 nearly linear spectrum of the nucleus, traversed by the 

 three bright bands characteristic of the light of comets 

 (which I have found in more than a dozen of these stars). 

 But on July 13, the evening of the last observation pos- 

 sible, the three bands had nearly disappeared, while the 

 spectrum of the nucleus was become much brighter. 



" Must we therefore conclude that the incandescent gas, 

 carburetted hydrogen or other, to which these bands are 

 due, disappear as the comet is developed, giving place to 

 the light, proper or borrowed, of the nucleus ? The ob- 

 servation of the new comet elucidates this. It rises 

 rapidly from the horizon, in the same region of the 

 sky where Coggia's coinet descended to disappear, too 

 quickly, below the horizon. Now on June 24 its spec- 

 trum, observed with the same instrument as was used in 

 1874, was reduced nearly to a continuous ribbon given 

 by the nucleus ; the nebulosity only gave a broad and 

 very pale band, well terminated on the more refrangible 

 side, diffuse on the other ; the other bands of comets did 

 not exist, or at least one could only suspect their exist- 

 ence in the neighbourhood of the nucleus. But yester- 

 day (June 26) the comet was already far from the horizon, 

 and when the sky was pure the three bright bands 

 appeared with great distinctness. The green band espe- 

 cially was bright, longer than the two others, and dis- 



tinctly limited on the less refrangible side (wave-length 

 516). On this side it seeemed bordered by a dark space, 

 as in the spectrum of Coggia's camet. As in the latter 

 the red is the only colour pretty visible in the spectrum of 

 the nucleus, and it is slightly dilated. The ulterior 

 observations will show whether these bands will continue 

 to develop. We are put on our guard, in any case, 

 against the effect resulting from difference of altitude of 

 the comet. 



"The total quantity of light given by the head of the 

 comet is considerable, and many persons have tried to 

 compare it to a star of the first magnitude. In reality its 

 intrinsic brightness is very slight. I had occasion last 

 night, by slightly displacing the telescope, to look at the 

 spectrum of a star of fifth or sixth magnitude ; the line of 

 light produced was at least as bright as the spectrum of 

 the nucleus." 



Admiral Mouchez having put at M. ThoUon's disposal 

 the 14-in. equatorial of the Observatory, the latter made 

 some spectroscopic observations of the comet on the 

 nights of June 24, 25, and 26, with the following 

 results : — 



" The nucleus of the comet gives a pretty bright con- 

 tinuous spectrum, on which one can distinguish neither 

 bands nor lines. The nebulosity surrounding the nucleus 

 gives three bands which are detached on a continuous 

 spectrum. One of them is very visible ; the others are 

 faint. Their position has been measured with great care. 

 The measurements, repeated a large number of times, 

 are more concordant than I could have hoped. 



" The spectrum of bands furnished by the comet so 

 resembles that given by the blue spirit flame that I con- 

 sider them identical. This identity does not result merely 

 from the aspect of the bands and their ratios of intensity, 

 but also from their absolute position. The spectrum of 

 the comet is, then, the spectrum of carbon or of one of its 

 compounds. The sole difference I have met with is that 

 the violet band given by alcohol is not seen in the spec- 

 trum of the comet ; the absorption of, the atmosphere 

 suffices to account for this difference." M. Thollon is 

 making further observations. 



NOTES 



The " Chelii' Memorial" volume takes the form of " Col- 

 lectanea Mathematica," and is issued under the joint editorship 

 of Professors Cremona and Beltrami (U. Hoepli, Milan). It 

 contains thirty papers by twenty-eight ."-ufficiently representative 

 mathematicians, of whom sixteen are well-known Italian vnriters; 

 of the remaining twelve, five (MM. Geiser, Kronecker, Reye, 

 Schlafli, and Wolf) write in German, four (MM. Borchardt, 

 Darboux, Hcrmite, and Mannheim) write in French. Of the 

 three English contributors, Messrs. Cayley (on a differential 

 equation). Hirst (on the complexes generated by two correlative 

 planes) write in English, and Prof. H. J. S. Smith discourses in 

 Latin "de fractionibus quibusdam continuis." There is a 

 likeness of Chelini. 



The Government have appointed the Earl of Crawford and 

 Balcarres Chief Commissioner, and Sir Charles T. Bright, Prof. 

 D. E. Hughes, F.R.S., and Lieut.-Col. C. E. Webber, R.E., 

 as Commissioners at the forthcoming Electrical Exhibition and 

 Congress at Paris. 



Students of Cretaceous- geology will regret to hear that 

 Griffiths, the well-known "fossil man" of Folkestone, has been 

 disabled for many months by rheumatism, brought on by constant 

 exposure during the past twenty-five years, in which he has daily 

 extracted from the wet and slippery tract of Gault clay in East- 

 weir Bay the remarkable series of moUuFca with their pearly 

 nacre preserved, plants, corals, Crustacea, and reptilian remains 

 that ornament not only the private collection of those who make 



