lOfi 



KNOWLEDGE. 



[July 2, 1900. 



and the increase of resolving power. Dr. S. Czapski has shown 

 that the greatest resolving power is obtained by using light of short 

 wave length, even the ultra-violet. This is due to the fact that 

 the blue end of the .spectrum has the shortest wave length, and the 

 limit of resolving power is one-half of the wave-length "of the light 

 used. 



In the course of his presidential address to the Quekett Society, 

 Dr. J. F. W. Tatham drew attention to a mounting medium con- 

 sisting of piperine and bromide of antimony, witli which he has 

 obtained very satisfactory results when examining lined tests. The 

 mixture is prepared by combining three parts by weight of piperine 

 and two of antim< ny bromide, by gently fusing the mixture over 

 a spirit lamp, care being taken not to raise the temperature more 

 than is necessary or it will chnr and discolour. After the diatoms 

 have been spread on the cover glass in the usual way, a small 

 portion of the mixture is placed between the cover glass and the 

 .slide, and gently fused until a thin film of it unites the two surfaces. 

 When the medium is set it mu.st at once be protected from the air, 

 otherwise the salts will decompose. To effect this solid paraffin 

 should be allowed to run between the cover glass and the slide, 

 and the whole finished off with a circle of Hollis's liquid glue. 



[All commuiiiodlions in reference to thin Column should be 

 addressed to .1/r. J. II. Cooke <it the Offiee of IvMiwi.EnGE.] 



NOTES ON COMETS AND METEORS. 



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



GiACOBtNi's Comet.— This object will be f.avourably visible :n 

 July, passing rather quickly through the con.stellations of Andro 

 meda, Lacerta and Cygnus. It will be nearest to the earth at 

 the end of the third week in .July when it will be about twice as 

 bright as it apjieared on the night (January 31) of its discovery. 

 The following is an ephenieris by Berberich (Ast. Nach. 3636, 

 for Berlin, mean midnight:— Distance of Comet 



E. A. Dec. in Millions o( 



Date, b. m. s. * Miles. 



Julv 2 23 .S6 32 -f 42 31 .. 125 



„■ 6 23 12 47 -H 44 21 ... 119 



„ 10 ... 22 44 43 -I- 45 52 ... 115 



„ 14 ... 22 12 29 -I- 4G 51 ... Ill 



„ 18 . . 21 37 4-1-47 7 ... 109 



„ 22 ... 21 16 -1 46 31 ... 108 



„ 26 ... 20 24 19 -H 45 o ... 109 



„ 30 . 19 51 16 + 42 42 ... 110 



Aug. 3 ... 19 22 21 + 39 51 113 



At noon on July 25 the comet p.isses 44' N. of Alpha Cygni, 

 and with a very low power may be seen in the same field of 

 view of a telescope on the nights of July 24 and 25. The position 

 of the star (January 1, 1900) is R.A. 20h. 38ni. Is., Dec. -f 44° 55', 

 while the places of the comet are — 



July 24, R.A. 20h. 42m. 2s., Dec. + 45" 52' 

 „ 2.5, „ 20h. 33m. Cs., „ -I- 4h° 27' 

 It will be interesting to view the comet and star if possible, 

 but the former will be somewhat faint, .and may be obliternteil 



^c^' 









4*^ 



+ 



s-s 



M 





^i' 



yy^S 







4- 



^if^.^' 



+)t 





Path of Cria'Mhiai's Coiuot amongst the Stars of C'vgnus and Lyra, 

 July 18— August 7, 1900. 



in the glare from the star. The comet should be looked for with 

 the star out of the field, and then the experiment can be afterwards 

 tried as to whether both objects are visible together. 



Comet 1892 II. (Denning). — M. Fayet, in "Bulletin Astrono 

 mique," for March, gives the result of his researches as to the 

 original orbit of this comet. M. Steiner has discussed (Ast. 



Nach. 3472) the present form of orbit, and concluded that it was 

 hyperbolic. The comet was observed during the 10 months from 

 March 18, 1892, to January 20, 1893. M. Fayet's investigations 

 show that it was origin.ally revolving in an elliptical orbit with 

 excentricity equal 0.998406. 



FiRED.\LT, OF March 28.— Prof. A. S. Herschel has compared 

 the various observations of this brilliant object and finds that the 

 most probable radiant was at 182" + 41", and the height of tlic 

 meteor about 60 to 38 miles above Kent. But the descriptions of 

 the path by the various observers are inconsistent and lead to 

 different results according to the interpretation put upon them. 



Fireball of May 5, 8h. 20m. — A very brilliant meteor was 

 noticed by many persons in the strong twilight of May 5, but, as 

 in the case of the fireball of March 28th, the accounts are some- 

 what discordant and incomjjlete as regards necessary details. The 

 following are extracts from a few of the reports already pub- 

 lished : — 



NoRTHANTS — Magnificent meteor, considerably larger th.m 

 Venus. Appeared in 8.F. sky, and sailed along the S. sky, cross 

 ing the meridian at about the altitude of the celestial equator, ami 

 finally bursting 30 degrees S.E. of the moon. . Duration 5 or 6 

 seconds. "It looked like a runaway moon charged with colour." 



St. Ai.ban's, Herts. — Meteor 4 or 5 times more brilliant than 

 Venus. It was first seen about 10 degrees S. of Arcturus and 

 disappeared about 4 degrees N. of the moon. Dur.ition 2 or 3 

 seconds. Sky partially cloudy. 



Bishop's vStortford. — Meteor of most startling and brilliant 

 nature spread itself over the zenith. It had a tail 6 degrees in 

 length. 



Handsworth, Birmingham. — Unusually bright meteor in the 

 E. part of the heavens, travelled slowly from N. to S., appearing 

 to take an upward course of about 45° with the horizon. 



Syston. — " A great luminous ball of fire " seen leaving a trail 

 of light behind it, and moving from E. to W. in an almost 

 horizontal line. 



Brighton. — " Extraordinarily brilliant meteor visible towards 

 the N.E. It swept along for some seconds, now hidden behind 

 clouds, now shining out in the intervals towards N.W. where it 

 disappeared." 



Ebbw Vale. — Fine greeni.sh meteor moved across the S.E 

 heavens very slowly from S. to N., its path being horizontal. 



LiDLiNGTON, Beds. — The body of the meteor was of large 

 size and very brilliant ; the tail was of great length. Its cour.se 

 across the sky from N.E. to W. occupied 3 or 4 seconds. 



Potter's B.^r. — First seen in the direction of Arcturus and 

 passed from S.E. to N.W. by W. Sailed a.cross the zenith, anJ 

 gave the impression of descending rapidly earthwards, the head 

 exploding quite low down. 



OxTON, Cheshire. — Fine meteor due S. when first seen, and 

 moving slowly towards S.W. ; not more than 25 degrees above 

 horizon. 



Birmingh.\m. — Brilliant meteor, twice as large as Venus, 

 " appeared rather low down in E. and was going almost due S." 

 Another observer says it travelled in a horizontal line from E. to 

 W. for about 30 degrees. 



W.^LSALL. — Very brilliant object gliding gently across Ihn 

 heavens and putting Venus completely in the shade. 



There are some other accounts. The observers generally de- 

 scribe the object as extraordinarily luminous, and moving rather 

 slow'y in a horizontal path from E. to AV. acmss the S. sky. The 

 real path of the fireball was from about 64 miles over Canterbury, 

 Kent, to 43 miles over Hungerford, Berks. Its length of cours.! 

 was at least 112 miles, and velocity about 20 miles per second. 

 The radiant point was a few degrees above the E. horizon at 

 245° -(- 5", but these deductions arc mere approximations. 



The Coming of the Perseids. — The last 12 nights of July will 

 be almost free from moonlight, and an excellent ojiportunity will 

 be aft'orded for observing early Perseids. They certainly begin 

 to arrive in the third week of July, and it is important that the 

 radiant point of the shower should be determined on eveiT night 

 from about the middle of July to the middle of August. Plentv 

 of observations have accumulated for the first half of August 

 and what we now require is a large number of materials for the 

 last half of July. For this puipose the sky should be watched 

 during the whole night, and the path-directions of the swift 

 streak-leaving meteors from the regions of Cassiopeia and Perseus 

 recorded witli great accuracy. The positions of the radiant as 

 deduced from the writer's observations in and since 1869 are as 

 f oUows : — 



