J.S 



KNOWLEDGE 



[Febbuaby, 1902. 



Ctonostoma. It has a circular disc of tentacles, which arc free 

 niul of one row only. Johnston's ' Brit'sh Zoophytes' is the 

 classical work on the ' Hyilroida' and ' Molluscoida,' hut if the 

 inquirer refers to Vol. 6, p. 4'20, of the ' Royal Nat. History,' 

 he will find an account of ' Paludieella,' together with a 

 Reotional woodcut of an individual animal." 



Correspondents who have assisted in this matter have taken a 

 considerahle amount of interest in it, and one in particular has 

 expressed a wish to have further material of a similar character 

 sent to him for investigation from time to time. 



A. If. (Ihiislrr. — There is no special advantage to be derived 

 from the use of a low-power ol)jective instead of an eyepiece, 

 but if you wish to experiment further, you will find that you 

 will do best bj' inverting the objective used as an eyepiece, so 

 that the light passes through it the reverse way, that is from 

 the back lens to the front lens. The field will then be equal to 

 the angle of the objective. The trouble attributed to the Abbe 

 condenser is in all probability due to the objectives which are 

 visuallj' corrected, and therefore ])hotographically over-corrected. 

 Racking the condenser high up has the same effect as shutting 

 the diaphragm, that is, it utihzes the under-corrected central zone 

 of the objective and thus produces a better ])hotographic effect. 

 A light filter, such as the acetate of copper solution referred to 

 in Knowi.eiii;e, February, 1901, or a GifEord's Screen, would 

 probably be found advantageous. 



ConsiiltaiiU. — An increasing number of correspondents send 

 material and specimens for identification and naming. It would 

 be of great assistance if readers who feel able to do so would co- 

 operate and act as honorary con.'-ultants in these matters. I 

 shall be glad to hear from such as are willing to assist, with 

 particulars of the subject they are competent to deal with. 



Communications and enquiries on Microscopical matters are 

 cordially invited, and should be addressed to M. I. CROSS, 

 Knowledge Office, 326, High Holborn, W.C. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.r.a.s. 



Comet 1900 II. (Boebellt-Bbooks).— In Ast. Nach. 3753, Mr. 

 J. M. Poor, of Princeton Observatory, N.Y., asks for unpublished 

 observations of this comet, as he intends to fonqnite a definitive orbit 

 for it. The comet was independently di-covered on July 23rd, 1900, 

 by M. Borrelly at Marseilles, and bv Mr. Brooks at Grenera. US. A., 

 the former having priority by about five hours. Tl»e object was fairly 

 bright, with a conspicuous tuil about one degree in length, and there 

 were two auxiliary tails or fiint off- shoots from the main ray. The 

 comet became very feeble at the end of September, and parabolic 

 elements apparently satisfied the observations. 



Enckk's Comet. — Though the position of this comet was by no 

 means favourable at his recent return, some excellent observations 

 were obtained at various European stations in the mornings of August 

 and September. In Ant. Nach. 3757, Herr H. Struve, of Eonigsberg, 

 gives the results of measures obtained on thirteen nights between 

 August 8th and September 4th, 1901, inclusive. Sig. A. Abetti, of 

 Arcetri-Firenze,also gives the positions on ten nights between August 

 9th and 23rd. On August 9th the comet appeared as a faint nebulosity, 

 without a nucleus, and about one minute of arc in diameter. 



FiHEBALL OF Decembee -Ith. — The writer has collected and com- 

 pared 02 accounts of this brilliant ohjeet, but tlie observations are 

 far from being satisfactory. The real path deduced from them is 

 therefore a little uncert«in, so that the exact height of the firebnU at 

 its first appearance and final disruption cannot be stated with 

 confidence. But there is no doubt that the approximate elevation 

 was from about 91 to 50 miles over the English Channel, a few miles 

 off the coast of Dorset, and that the direction was from W. to E., 

 with a slight southerly inclination. The streak of the meteor was from 

 72 to 55 miles high, and 26 miles in length. Several corres]iondents 

 refer to a hissing or rushing noise which accompanied the lliglit of 

 the object, while others say that its passage through the air was 

 performed in absolute silence. The great niajoi-ity of the observers 

 heard nothing, and it is obvious that any detonation proceeding from 

 the disruption of the fireball could not have been heard until several 

 minutes after the phenomenon had disappeared. In describing the 

 fireball of September 14th last, brilliantly visible over South Wales, 

 several of the spectators stated that they distinctly heard a hissiug 

 sound simultaneously with the meteor's descent. This is, in fact, a 

 common feature of such observations, but there is no doubt that the 

 impression is an erroneous one. The rushing noise which accompanies 



the flight of a rocket is familiar to everyone's ears, and amid the 

 s'lrprise occasioned by the sudden apparition of a brilliant rocket-like 

 meteor, ths imagination is naturally incited to receive a similar 

 sensation. 



FiBKiiALL OF Decembee ICxn.— In the early evening, at 5h. 45m., 

 a brilliant meteor was witnessed by .Vlr. W. E. Kesley at London, by 

 Mr. Jo nson at Bridport, and by an observer at Veovil. At Kridpjrt 

 the object was estimated to bo a» br ght as the moon in her rjuarters. 

 It moved slowly and vanished near Venus. As seen from Veovil. the 

 meteor descended in a path parallel with the moon and Venus, and 

 somewhat ca^t of them. The object was probably a late Geminiil, 

 moving from N E to 8.W. over the English Channel, west of Guernsey, 

 and falling from 08 to 54 miles. The length of path was upjiroximately 

 51 mdes, and velocity 20 miles per second, but these results are 

 somewhat unceriain, and it woukI be useful to hear of further 

 observations. 



FiBEBAiL OF December 19th. -At about 0.45 a.m. on this date a 

 very large meteor was seen in the north of Kngland, but it appears to 

 have been very inadequately observed. Police-Constable Clarke, of 

 Haworth, writes to the Scarborough Merciirii that he saw a bright 

 light, and on looking up noticed a very large body of some kind 

 travellirg along at about the height of an ordinary mill chimney. 

 The object was about as big as the largest ship he had ever seen. It 

 travelled ticm E. to W., and it went out in the neighbourhood of the 

 seven stars (Pleiades). It was visible for 14 minutes, and left a tail 

 behind it. 



THE FACE OF THE SKY FOR FEBRUARY. 



By W. Shackleton, f.r.a.s. 



The Sun. — On the 1st the sun rises at 7.4"JI am., and 

 sets at 4.4G p.m. On the 28th he rises at 6.52 a.m , and 

 sets at 5.85 p.m. The sun appears to be in a very 

 quiescent state, and there is quite a dearth of spots. 



Towards tlie end of the month the Zodiacal Light may 

 be looked for in the west shortly after sunset. 



The Moon: — 



The more interesting occultations visible at Greenwich 

 are as indicated in the foUowin? table : — 



The Planets. — Mercury is an evening star, and has 

 an easterly elongation of 18° 17' on the 3rd. About this 

 time the planet will be favourably situated for observa- 

 tion, as he remains about Ih. 45m. above the horizon, after 

 tbe sun has set. The ])ath of the planet lies in Aquarius 

 and makes a loop around the fourth mao:nitude star 

 Aquarii. On the 2ud of the month it has the same 

 R.A. as the star, but is 2^" to the south, its motion being 

 easterly, and on the 16th it again has the same right 

 ascension as the star, but is 1° to the north, its motion 

 being westerly, bringing it into inferior conjunction with 

 the sun on the l8th. 



Venus, also in Aquarius, is an evening star for a few 

 days in the earlier part of the month, but its rapid retro- 

 grade motion brings it into inferior conjunction with the 

 sun on the 14th. On the 1st of the month it sets about 



