46 



KNOWLEDGE 



[February 1, 1901. 



aud bavins,' fixed to it two springs, S, S. By means of these 

 springs tlie slide is held in position on the carrier, and the 

 carrier is also held in position between the upper and lower 

 platts of the stage. The ^li<^e can be roughly adjusted by means 

 of the carrier, fine adjustment being made with the mechanical 

 stage. The heating apparatus is as in Fig. 3, and by slightly 

 raising or lowering the flame, the temperature can be regulated 

 and kept constant within half a degi'ee Centigrade. 



Light Frr.XERS. — A few years ago it was pointed out by 

 Mr. Nelson that the use of suitable light filters improved the 

 working of objectives in a marvellous manner, that if the filter 

 employed was practically of the same colour as the ray for which 

 the spherical aberration of the objective was best corrected, a 

 good modern achromatic lens would perform equally as well as 

 an expensive apoehromat. 



The most practical and successful of light filters at present 

 in use consists of a saturated solution of acetate of copper. 

 This should be placed in a trough and intervene between the 

 illuminant and the substage condenser. 



The internal thickness of this trough should not be less than 

 i inch ; -^-,j inch barely causes the absorption of the red in the 

 spectrum, | inch exactly does it with an oil lamp having a 

 i inch wick. If a more brilliant illuminant be used, a greater 

 depth of trough can without disadvantage be employed. We 

 recommend a trial of this medium to all workers who would 

 improve the definition of their object glasses. 



Another advantage of a light filter of this description is that 

 the full cone of the substage condenser can be used without the 

 brilliance of illumination being so great as to cause the observer 

 discomfort. 



Notes and Queries. — Com>nmi/ra*ions and enquiries im 

 Microsnopical matters are cordially inrited, and fthoidd he 

 addressed to M. I. CROSS, Knowledge Office, 3'2(j, Ilir/h 

 Ilolhoni, W.C. 



♦ 



NOTES ON COMETS AND METEORS. 



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



CoMETAET DiSCOTEEIES DURINft THB NINETEENTH CeNTTJET. — 

 The extraordinary progress effected in all departments of astronomy 

 during the past century is well exemplified in that branch relating to 

 conaefcs, for there were nearly four times as luany new comets found 

 between 1801 and 1000 as lietween 1701 and 1800, the relative numbers 

 being 235 aud 62. The century just concluded lias, in fact, furnished 

 us with many important items respecting these my.steriou3 bodies. 

 In 1800 only one periodical comet was known, viz., that of Halley's. 

 At the present time we arc acquainted with a large number, which 

 are gi'ouped into families, the most numerous and best known being 

 those with aphelia, just outside the orbit of Jupiter. During the 

 century just opened the field of cometary discovery will no doubt 

 continue a very productive one, but it is not likely that the figures 

 will show a great increase as compared with the last century. The 

 rate of these discoveries has not exhibited any marked rise since rlie 

 year 1810, and it is difficult to see how it can bo much accelerated 

 imless a more expeditious means of seekingfor these bodies is adopted, 

 or many more observers than hitherto apply themselves to the work. 



CoiiET 1894 IV. (De Vico— E. Swift).— It is expected that this 

 comet will arrive at perihelion on February 13th, but it will then be 

 overpowered by the rays of the sun. 



Beoesbn's Comet. — This comet is moving rapidly to N.W., and 

 ought to be well visible iu February. No annouucement of its 

 re-discovery has, however, yet been made. In view of the fact that 

 the comet has eluded detection at several previous returns its existence 

 is a little questionable, aud there appears some ground lor the 

 inference that it has, like the comet of Biela, suffered disintegration. 

 It will, however, be diligently sought for by means of some of the 

 large telescopes available for this kiud of work, and we may shortly 

 expect to liear of its re-detection if it revolves iu the same orbit as 

 formerly, and still visibly exists under the form of a comet. 



New Cojibt. — Anew comet is announced as having been discovered 

 by M. Giaeobini, at Nice, on December 20th. Its apin-oximate 

 position was R. A. 338°. Dec S. 22°. On December 2-lth, 8h. 43m., 

 G-.M.T., its place was R. A. 344i», Dec. S. 22|°, so the object is moving 

 about li'' per day to the E.S E. During the last iew years M. 

 Giacobini's discoveries of comets have been rather numerous and 

 important, and in recognition of his successful labours iu this field 

 the French Academy of Sciences has recently awarded him the 

 Lalande Prize. 



Autu.mn Meteors. — In October and November Prof. A. S. Hei-schel, 



of Slough, observed 120 meteors, and determined the positions of the 

 chief radiants as follows :- 57° + 9° (11 meti-ors', 57° + 18° (11), 

 50° -H 28° ,8), 70° -t- 35"^ 8). 80° + 18° (6i, 75° + 13- (4), 44° + 24° 

 (9), 44''-i- 1-^° (10, The firat two radiants represent well-defined 

 sliowers of Taurids. 



The Geminids. — On Decembpr 13th the sky was beautifully clear, 

 and a number of meteors were observed at various places. At Slough 

 Prof. Herschel watched from llfh. to 13Jh- and recorded about 20 

 meteors, including tno fine ones, as follows : — 



llh. 58ra. — Magnitude twice as bright as Venus. Path of about 

 35 degrees from ^ Persei to halfway between j3 and y Arictis. 

 Probable radiant 167° + 5°. 



lih. 2Gm. — Magnitude equal to Jupiter. Path from 1° N. of 

 X Orionis to 1° S. of 7 Tauri. Moved over 30'' in f second. Probable 

 radiant 121° - 1°. 



About one-third of the meteors seen were Geminids with the usual 

 short tracks and quick motions. 



Mr. T. H. Astbury, of Wallingford, watched the sky on December 

 13th between 8h 10m and Oh. o'clock, and registered 14 meteors, of 

 which 12 were Geminids, the centres of radiation being 109° -I- 35° 

 and 113° -I- 32°. A later observation from 9h. 50m. to lOh. 30m. 

 furnished three additional Geminids, but the shower appeared to 

 have greatly declined as compared with its unusual activity earlier in 

 the evening. 



Mr. C. L. Brook, at Meltham, near Huddersfield, observing for 

 2^ hours on December 11th, between 9b. and l2li , saw 19 meteors, of 

 which 11 were Geminids. On December 12th he watched 3h. 25ni. 

 of the interval between 8h. and 12jh., and saw 25 meteors, including 

 17 Geminids. Between lOh. 51ui. and llh. 35m. no less than 

 13 Geminids were recorded. 



On December 13th, lOh. 18|m., a rather fine J Geminid, brighter 

 than a first magnitude star, was observed by Mr. A. King, of Leicester, 

 and Mr. T. H. Astbury at Wallingford. The meteor fell from a 

 height of 59 to 44 miles, and its course lay from nearly over Hertford 

 to Luton. Length of path 24 miles, and earth point 8 miles west of 

 Banbury. 



FiEEBALis. — Several of these striking objects have been recently 

 observed from various parts of the country. The dates aud times 

 were as under: — November 27th, llh. 10m. ; December 1st, 4h. 12m. 

 and 12h. ; December 10th, 3h. 55m. a.m. ; December 16th, 7h. 35m. 

 a.m. ; December 17th, 5h. 55m. p.m. Mr. G. Herbert Price, of 

 Brixton Hill, S.W., also reports a bright meteor seen on December 

 13t.h, 9h. 20m , traversing a path from Gemini to the region of Aries. 

 A rather sensational incirleut occurred on Saturday night, December 

 22nd, according to the Pall Mall Gazette, which states that "a large 

 meteorite fell at'Great Parndor, Essex. Frederick Armour, a local 

 postman, who was passing the field in wdiich it fell, states that he was 

 blinded and stunned by the brilliant fiash of light. He was found 

 unconscious iu the roadway." 



Fireball in Sunshine. — On January 6th, 1901, at Oh. 52m. 

 p.m., a large meteor was observed from various places in Scotland 

 and the extreme N. of England As seen from Glasgow the object 

 is described as a large ball of fire with a long streaming tail. The 

 meteor disappeared in the N.W. quarter at rather a low altitude, 

 and it was directed from the E.N.E., so tliat the probable radiant was 

 in the region of Perseus or Aries. Mr. W. H. S. Monck has kindly 

 sent me several newspaper accounts of the fireball, but they are 

 wanting in some of the definite particulars necessary for the computa- 

 tion of the real path. There was a brilliant meteor seen in sunshine 

 ou January yth, 1900 (see Kxowledoe. February, 1900, p. 47), but 

 this object must have emanated from a different stream to that which 

 furnished the more recent meteor. It is astonishing how many large 

 meteors have been observed even in the presence of the sun, and it 

 proves that they are unusually prevalent in the day-time. Unfor- 

 tunately, however, they are seldom well observed as regards their 

 position and direction of fiight. 



THE FACE OF THE SKY FOR FEBRUARY. 



By A. Fowler, f.r.a.s. 



The Sun.— On the 1st the sun rises at 7.42 a.m., and 

 sets at 4.46 p.m. ; on the 28th he rises at 6.51 a.m. and 

 sets at 5.35 p.m. Few sunspots are to be expected. The 

 Zodiacal Light may be looked for in tlie west after 

 sunset. 



The Moon. — The moon will be full on the 3rd at 

 3.30 P.M., will enter last quarter on the 11th at 6.12 p.m., 

 will be new on the 19th at 2.45 a.m., and will enter 

 first quarter on the 25th at 6.38 p.m. The following 



