246 



HAE-DWICKE'S SCIENCE-GOSSIP. 



were going up over the path for a long time, and 

 when I looked at them again, tliey had all, as if by 

 one consent, turned, and were progressing along at 

 right angles to their former course ; for what reason 

 I was not able to find out. The owner of the 

 furthest-up mill in the valley tells me that his mill- 

 pond used to be piled up with spawn, but since 

 some change of chemicals used in work, there had 

 been less than there used to be. I am told both 

 the ringed snake and the adder were rather plenti- 

 ful. I only saw one of the former snakes. 



In conclusion, I may notice, with reference to 

 Mr. F. Stratton's interesting article on variation of 

 colours in flowers, a pinkish-red variety of the 

 common yarrow or millefoil {Achillea millefoliim) , 

 which occurred plentifully in company with its 

 usual white-flowered form. I have also seen the 

 same variety at Erith, and think it is a pretty com- 

 mon variety. Is white the normal colour of the 

 flower ? 



I forgot, while on the subject of geology, to 

 mention that a very fine specimen of a molar tooth 

 of an elephant, most probably the fossil U. primi- 

 genius, was dug out of a superficial deposit at 

 Stroud, and a gentleman residing at Bisley, who 

 had this tooth, showed me some boars' tusks he 

 had found in that neighbourhood. 



Southampton. Hakry Leslie. 



SPECULATIONS CONCERNING THE USES 

 OF COMETS IN THE UNIVERSE. 



By John I. Plummek, M.A. 



THOSE who have endeavoured to push scientific 

 research into the realms of the unknown, 

 cannot fail to have remarked how numerous are the 

 hypotheses which at one time or another have 

 engaged their attention, each in its turn to be re- 

 jected, when it fails to receive confirmation by 

 agreement with observed facts. Such is the method 

 of scientific progress, which advances only on the 

 wreck of misconceived theories. Yet it frequently 

 happens that these " guesses at truth " may contain 

 the germs of important discoveries ; for how often 

 will it occur that he who originates the theory is 

 without the means of testing it by experiment, or 

 is unable to pursue those observations upon Nature, 

 specially designed for the purpose, that may be 

 necessary before it is possible to pronounce upon 

 the truth or falsehood of a favourite proposition. 

 These remarks apply more particularly to the case 

 of astronomy, a science in which all the more ordi- 

 nary phenomena have received their appropriate 

 solutions, and in which the explanation of the more 

 infrequent will often require years of observation to 

 verify. May we not therefore conclude, that while 

 it would not be advisable to publish these unesta- 



blished theories in the purely scientific journals, 

 they might well find a place in Science-Gossip, so 

 that what is incomplete, hazy, doubtful, in the 

 mind of one may be improved, confronted by obser- 

 vation, and developed by another? Moreover it 

 may be remarked that any theory, even though 

 erroneous, provided it explain some portion of 

 observed data, is useful. A bad theory is often 

 better than none at all. No better example of the 

 truth of this paradoxical assertion can be given than 

 the celebrated but now utterly discarded law of 

 Bode, which suggested to Olbers nearly a century 

 ago, the possibility of a planet situated between 

 Mars and Jupiter having been dashed to fragments 

 by some catastrophe. We now know that Olbers' 

 theory was as erroneous as Bode's, but we are 

 nevertheless indebted to the bold enunciation of 

 these false suppositions for the discovery of the 

 group of the asteroids, whose numbers now fast 

 approach one hundred and fifty members. Happily 

 it would seem very unlikely that astronomy is in 

 any danger of being overburdened with these 

 theories. No part of the celestial economy, save 

 perhaps the comets, admit of much speculation, and 

 perhaps an attempt to guess at the part they play 

 in the universe may assist in unveiling the mystery 

 that has always hung about these bodies. 



In the first place, there seems some reason to 

 complain that their weight and importance have 

 been considerably under-estimated. The facts relied 

 upon by those who believe in the insignificance of 

 comets are, first, that Lexell's Comet in 1779 

 passed very near to Jupiter without producing any 

 marked disturbance among the satellites of that 

 planet, and, secondly that Encke's Comet has 

 passed near to Mercury, also without causing any 

 observable perturbations. Both these bodies are, 

 or were, members of that group of periodical comets 

 which revolve round the sun in periods not greater 

 than seven years, admittedly the smallest and 

 faintest of their class. The latter has no stellar 

 nucleus, and may well be a body of slight mass, and 

 the former has not been seen since 1770, having 

 been diverted from its orbit by the powerful attrac- 

 tion of Jupiter ; nor am I aware whether any record 

 remains of its appearance to enable us to judge 

 relatively of its dimensions or mass. Another fact 

 suggesting the impalpability of comets is the trans- 

 parency of their tails, coma;, envelopes, &c.,* which 

 would be a fact of little importance in itself, but 

 which strengthens an opinion already formed of 

 their imponderability. On the other hand, the 



• It is often asserted that stars have been seen through the 

 nucleus of a comet, but this is doubtful, at least in the case 

 of comets with stellar nuclei ; in the case of comets which 

 have only a condensation at or near the centre ot the coma, 

 it is not unlikely that they may be transparent, but the 

 opportunity of seeing a star so centrally situated must occur 

 very rarely indeed. 



