186 



♦ KNOWLEDGE ♦ 



[Dec. 16, 1881. 



coinu't tloulilc on January 1.1; luit Wiclmiann observed it 

 lis a single comet on tho 1 Gtlu But Professor Challis, in 

 his account of his own oluscrviitions on the comets, stat<'s 

 tlmt even on January l.'i tho second comet might ea.sily 

 have lieen overlooked. M. Valz saw nothing unusual on 

 the 18th and 'JOtli ; l>ut on the 27th; "I was struck with 

 amazement," he says, " to tind two nebulosities, separated 

 by an interval of two minutes of arc, instead of one 



nebulosity alone Eacli head was followed by a 



short tail, wliose direction was perpendicular to the line 

 joining the two nebulosities." Earlier, only the larger 

 fomet had had a tail, the appearance presented by the 

 double comet being that ."ihown in Fig. 2. 



Tlie two comets travelled along, side by side, until at 

 la.st both passed out of view, at which time the distance 

 between them amounted to about 157,000 miles. 



In 18.t2 both comets returned. Sir John Herschel says, 

 in his " Familiar Lectures on Scientific Subjects," that 

 when they returned, the distance between them was un- 

 changed. Tliis, however, was a mistake. The distance 

 now amounted to about 1 ] millions of miles. Again they 

 passed before the interested gaze of astronomers, travelling 

 side by side, tliough rather far apart, until finally tliey 

 disappeared from view — we say finally, for neither lias 

 ever been seen again. 



Whether the two comets returned in 18-59 is doubtful. 

 It is certain that if they did, they would have been in^-isible, 

 for the same reason that the comet was invisible when it 

 returned in 1839. 



But in 1866 thedoulile comet should have been well seen. 

 It should be remembered that each return of a comet of 

 short period (like that which our correspondent Mr. F. 

 Denning, of Bristol, discovered this year) gives the astro- 

 nomer more perfect mastery of the comet's motions. The 

 return could be predicted with sufficient accuracy in 1832 

 to cause the comet to be easily redetected. The next visible 

 return might have involved a difficulty, because the comet 

 had in the interval made two circuits. But that return 

 was successfully predicted. The return in 1845-16 was 

 .still more accurately calculated. Nor did the breaking up 

 of the comet into two on that occasion interfere with the 

 successful calculation of the return in 1852. The case may 

 he compared to the rating of a clock, which is more satis- 

 factorily efiected in a week than in a day, for the simple reason 

 that any error of observation is spread in one case over seven 

 times as long a period as in the other, and therefore aflects 

 the estimate of any given circuit of the hands by an error 

 only one-seventh as large. Just so, whatever error an astro- 

 nomer might make in observing Biela's comet in, say, 1843, 

 was distributed over all tlie revolutions of the comet which 

 had taken place since 182G (one might almost say since 

 1772), and in a correspondingly small degi-ce affected the 

 astronomer's estimates of the comet's motion during any 

 single revolution. This being so, astronomers had good 

 reason for believing that in 186G Biehi's comet would 

 return. 'When the time came that it sliould have been 

 \i8ible, telescopes were turned towards the spot where 

 it should liave been seen. Xight after night from 

 that time its calculated track was swept with the 

 finest telescopes in Europe and America. But no 

 trace of the comet could be seen. " It is now," 

 wrote Sir John Herschel, in February, 18G6, " over- 

 due. Its orbit has been recomputed, and an ephemeris 

 calculated. Astronomers have been eagerly looking 

 out for its reappearance for the last two months, when, 

 according to all former experience, it ought to have been 

 conspicuously visible, but without success ! giving rise to 

 the .strangest surmises. At all events, it seems to have 

 fairly disappeared, and that without any such excuse as in 



the case of Lexell's — the preponderant attraction of some 

 great planet. Can it have come into contact, or exceed 

 ingly close approach to some asteroid as yet undiscovered ; 

 or, peradventun-, plunged into and got bewildered among 

 the ring of meteorolites, whicli astronomers more than 

 suspect 1 " 



Be the cause what it might, the comet was not seen in 

 1866. In 1872 it wa-s looked for even more carefully. 

 Every possible contingency depending on planetary per- 

 turtiations was considered ; and the telescopes of a.stroao- 

 nu?rs swept, not only the calculattxl path, but ta a con- 

 siderable distance on either side of it. No trace of the 

 comet was seen, however, in 1872 any more than in 1866. 

 Bo far as tele.scopic observation is concerned, Biela's comet 

 seems to have come to the end of its career as a comet. 



Yet the observations of 1852 were not the last which 

 were made on this interesting object. It has been seen 

 again, though not as a comet. Nay, the occasion on which 

 it was seen in the way referred to was predicted, and the 

 prediction fulfilled, even in details. We shall return to 

 the consideration of this remarkable apparition of the 

 comet in changed fonn — a form which but a quarter of a 

 century ago no one would have thought of associating in 

 any way with the long-tailed star whose approach had 

 been regarded as heralding some great change in the 

 fortunes of men and nations. 



TOAD IN A HOLE. 

 Bv Dr. a. WiLso.N, F.R.S.E. 



IX letter 87, " Arachnida " asks, " What is tke eonstmction of 

 tlic common toad that enables it to be enclosed for many years 

 in blocks of soUd matter ? " " Arachnida" should first of all hare 

 asked, is it true tlmt loads aie ever found so enclosed 'i The usnal 

 story is that of some quarrj-men, who, blasting stones, see a lire 

 frog or toad hopping about, after the blast, among tho dehrii. 

 Because tho toad is found thus, it is assumed that it came from the 

 interior of the rock. Xot a particle of evidence exists to show in 

 such a case that the animal had anything whatever to do with the rock. 

 If " Araclinida " will read in the " English Cyclopaedia " the account 

 of Dean Buckland's experiments, he will find that the Dean 

 enclosed healthy frofjs and toads in holes cut in limestone and 

 sandstone blocks. He buried the blocks in his parden three 

 feet deep. At the end of the first year most had died, and 

 tho living ones, rc-buricd, all died long before the end of the 

 second year. Common sense, apart from exact knowledge, would 

 tell us that animal life of higher kind, >rith all its demands in the 

 way of food, lic, could not exist under the circumstances of the 

 popular tales and superstitions " Arachnida" inquires about. Tho 

 oldest fossil toads and frogs occur in Tcrliaru rocks. If, there- 

 foj'c, a live toad liopped, as has been alleged, out of a Cretaceoiti 

 or Devonian rock, such a fact would amount to the declaration that 

 the live toail could be ages and ages older thnn its fossil rela- 

 tives, wliieh declaration is, of course, the height of absurdity. 

 There is no doubt that a frog or toad has an elastic constitu- 

 tion. It is cold-blooded ; it can live under water for months ; it can 

 live for months after excision of its lungs, because the skin takes on 

 the functions of lungs in snch a case ; and these animals (as in 

 Dean Buckland's experiments) can live without food for a year or 

 two, but, like all other animals (and plants), ilic starved and meagre, 

 sooner or later. If "Arachnida" will only take the trouble to 

 inquire into tho evidence on which such stories as those he mentions 

 ore founded, he will find not one single proved or provable fact 

 which will warrant any belief in the utterly impossible existence of 

 toads or frogs in rocks. I may refer him for a fuller account of 

 snch coses to the essay on " Some Facts and Fictions of Zoology" 

 in my " Ivcisure Time Studies " (Chatto A Windus). As a naturalist, 

 I stake my reputation on the correctness of the riews stated above, 

 and also repeated in my book. 



Pond's Kxtkact is a certain cure for Rhoumftti.«in and Gout. 

 Pond's Kitmct is a certain cure for lla-morrhoida (Piles). 

 Pond's Kxtroct is a certain cure for NeuralKio pains. 

 Pond's Kxtract mil heal Bums and Wounds. 

 Pond's EitracI will cure Spnsins and Bruise«. 



S^'ld by all Chesnists. Get the genuine. [Al>rr. 



