July 9, 1874] 



NATURE 



181 



such spectra as these that we shall see, and not line spectra. 

 Further, in the case of compounds in which the mole- 

 cules which give us these ncv/ spectra enter into combina- 

 tion, we may possibly dissociate them and observe their 

 spectra at a much lower temperature than we can drive 

 the higher molecular arrangement of the solid into vapour, 



Such considerations as these derive additional interest 

 and importance from the beautiful researches of Schia- 

 parelli, which connect comets with meteorites. 



Modern science acknowledges that comets are indi- 

 vidual members of meteor swanns — not that meteors are 

 comets' tails, as some think ; this idea is, one may say, 

 impossible to reconcile with facts — that one difference 

 at any rate between a comet and a meteor is that 

 one is self-luminous, the other is not till it arrives within 

 the limits of our atmosphere. If this be acknowLcJ^^cd, 

 then to what is this difference to be ascribed ? A possible 

 cause is certainly a difference of chemical constitution — 

 a difference between materials incandescent at a high tem- 

 perature and materials incandescent at alow one. It is not 

 necessary to stop to inquire how this temperature has 

 been arrived at, but it is important to show that the ques- 

 tion of temperature is one of the very first points to be 

 attended to by those who can bring sufficiently powerful 

 instruments to bear upon the present comet, and that the 

 question of its actual chemical constitution is bound up 

 with it. 



But whatever be the temperature of the head there is 

 another point which must not be lost sight of Sir John 

 Herschel writes concerning Halley's comet : " The bright 

 smoke of the jets, however, never seem to be able to get 

 far out towards the sun, but always to be driven back and 

 forced into the tail, as if by the action of a violent wind 

 rolling against them — always from the sun — so as to make 

 it clear that this tail is neither more nor less than the ac- 

 cumulation of this sort of luminous vapour, darted off in 

 the first instance towards the sun, as if it were something 

 raised up, and as it were exploded by the sun's heat, out 

 of the kernel, and then immediately and forcibly turned 

 back and repelled from the sun." Here we have the 

 question raised not only whether the envelopes consist of 

 different materials, but whether the tail is not entirely or in 

 part self-luminous : the present comet may show that this 

 point is not so satisfactorily settled as it is supposed to be 

 in favour of reflected light. 



Such then are briefly some of the questions at issue. 

 It is to be hoped that our beautiful visitor will answer 

 some of them for us, and that when it leaves our northern 

 skies the work may be carried on in the southern hemi- 

 sphere. J. Norman Lockyer 



THE CHANNEL TUNNEL 



WE fear there are still many who fail to see that any 

 good can come of scientific research unless it has 

 some well-defined " utilitarian " object in view. Even in 

 this and in other countries that are in the van of civilisa- 

 tion and in which education is comparatively wide-spread, 

 the majority of mankind can appreciate a benefit only 

 when it takes a concrete and tangible form. That love 

 of knowledge for its own sake, that noble inquisitiveness 

 which has been so fruitful in results during the last two 

 hundred years, even yet belongs to comparatively few, 

 who are still regarded by the many with a kind of im- 



patient pity as mere unpractical hobby-riders. Still the 

 people who talk in this way are proud enough of the 

 glory which their great men have shed upon their country, 

 and would not willingly, we believe, part with it for money 

 were this possible ; and indeed how would this country 

 appear among the nations were she deprived of the 

 inestimable inheritance which her great sons have 

 bequeathed to her in every department of intellectual 

 activity ? Happily, however, the race of those who decry 

 single-eyed scientific research is getting sensibly smaller ; 

 and we firmly believe that as education improves and 

 as higher education spreads, carrying with it the results 

 of this same scientific research, it will disappear. 



Still, a little consideration might show those who are 

 ever ready to cry "what's the good .?" that since all so- 

 called ''practical " schemes are concerned either with man's 

 own body or with the surrounding universe, an essential 

 part of the basis of any scheme is a thorough knowledge of 

 the material on which it is proposed to work. Such a know- 

 ledge it has over and over again been shown is only to be 

 attained by abstract scientific research, by investigation 

 conducted as if the only end in view were a thorough 

 knowledge of the subject in hand in all its scientific 

 aspects and. relations. Many instances could be given, 

 and indeed are every day occurring, of the highest 

 practical results unwittingly following from such investi- 

 gations ; and to the sceptic we could not recommend a 

 better example of how indispensable is thorough scien- 

 tific research as a basis for the useful arts than the 

 results of the investigation into the geology of the Chan- 

 nel which Mr. Prestwich (the newly elected O.xford 

 Professor of Geology) presented to the Institution of 

 Civil Engineers last December, and which, with the sub- 

 sequent discussion and maps, has just been published in 

 a separate form. This study of the strata which underlie 

 the Cliannel, and which seems to us an almost perfect 

 e.KampIe of close and careful reasoning on physical facts, 

 is now brought forward to enlighten the projectors of a 

 tunnel between England and France as to the nature of 

 the material with which they will have to work ; but Mr. 

 Prestwich distinctly stites that the various formations 

 are considered " irrespective of their relative merits in 

 any other than a geological point of view." 



Mr. Prestwich's plan is to discuss carefully all the strata 

 which underhe the Channel, from the London clay down 

 to the Palaeozoic series, exhibiting distinctly their litho- 

 logical characters, dimensions, range, and probable depth, 

 and from these data deducing his conclusions as to the 

 suitability of each formation for being pierced by a tunnel. 

 The investigations of himself and others on which Mr. 

 Prestwich's paper is founded were mostly undertaken from 

 no practical point of view, and before a Channel tunnel 

 was thought of. Mr. Prestwich, many will be glad to 

 think — grateful, we hope, at the same time for this very 

 practical result of pure scientific research — concludes 

 that from a geological point of view it is quite practicable 

 to construct a tunnel underneath the Channel, although 

 to do so with safety it will be necessary to go very deep 

 down. But an excellent idea of the results of the investi- 

 gation will be obtained from the following clear summary 

 with which Mr. Prestwich's paper concludes : — 



" In the London clay there exists a perfectly impermeable 

 bed of sufficient thickness, but nowhere between the two 



