2R6 



KNOWLEDGE. 



[Decembbb, 1902. 1 



Xotliing is more popular than the jirojection of i)oiid life 

 upon a screen; as this is a suhj.^ct which, in the exhihiting of the 

 commoner and larger forma, does not call for the use of high 

 ma'jnifications, it can he done with fucility. Specimens to be 

 exhibited should he placed in a trough having a small interval 

 between the base and the cover, so as to keep the objects, so far 

 as possible, in one plane. Also the area for free swimming 

 should be a restricted one. Rotifers and some of the smaller 

 subjects could be well shown by placing them in an excavated 

 8li|> .and covering them with a thin cover-glass ; compressors 

 and live-cages also have their uses. 



]$ut apart from this one subject there is a large range of 

 general objects which would always prove of interest, and the 

 suggestion of selfishness which is frequently attributed to the 

 niicroscopist, working by himself, would be removed, and an 

 opjmrtunity afforded of giving interesting pleasure to many 

 others. 



NOTES AND QUERIES. 



C. Iplon.—l would dehydrate the lichen in absolute alcohol. 

 Clear in clove oil, then wash away all trace of oil with repeated 

 changes of benzole or naphtha ; infiltrate and embed in paraffin 

 wax ; cut sections, wash away paraffin with benzole or turpentine 

 and mount in Canada balsam. 



Seco. — The photographs you send are very nice and sharp. 

 Xo. ] seems to be correctly exposed, but No. '2 appears to be 

 a little over exposed : the detail, however, is nicely shown. 

 The method of ascertaining the magnification when photo- 

 graphing is to project the line of a stage micrometer on the 

 ground-glass screen, and then by measuring the intervals between 

 the magnified lines the magnification can be at once known. 



C. Pnulter. — Both the specimens you send are Sertidaria 

 opei-culata. 



G. n. Johnson. — Your query is replied to by the notes 

 which appear in these columns. 



H. Taiflor. — It is a little difficult to reply to your question 

 without knowing how your objects are mounted. As you 

 incidentally mention pond life, it is to be assumed that you are 

 trying to get a dark ground illumination with objects in troughs. 

 I would suggest that, first of all, you tried to get a black back- 

 ground with an ordinary transparent mounted object such as 

 spicules of sponge or diatoms. With an Abbe Illuminator you 

 will find it necessary to let the front of the top lens practically 

 touch the object glass, aud it is essential that the black patch 

 stop that is used shall be of suitable size. Also do you s-hade 

 the light of the lamp from the upper side of the stage of the 

 microscope? "With these precautions there should be no 

 difficulty in obtaining a good black background with the 

 arrangements you make when using the 1-inch or J,-inch, but 

 j'ou must not expect a black background with a ji-inch objective. 

 You might get an inferior one by using the Iris Diaphragm at 

 the back of the objective, but it is really not worth the 

 trouble. 



0. Healh. — I know of no work that gives the anatomy of the 

 whole order of Insecta ; there are special bonks such as Huxley's 

 " Invertebrata ■' which gives an account of the cockroach (£/aWa 

 ririentftlix), commonly known as the "black beetle,'" Lowne's 

 "Anatomy and Physiology of the Blow-fly,'' and Miall's 

 " Harlequin Fly.'' Packard's " Entomology for Beginners" is 

 an excellent wullum in parvo. Have you a copy of Kirby and 

 Spence's book on insects V This is at once one of the most 

 informing and interesting books you can read. 



Communicatinns and enquiries on Microscopical matters are 

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

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



NOTES ON COMETS AND METEORS. 



By W. F. Denning, p.k.a..s. 



Perrine's C'oukt (1902b). — This comet passed throiigli its peri- 

 helion on the morning of November •24th, and has travoUed too far to 

 the south to continue visible to nortliern observers. It was at its least 

 distance from the earth on October 8th, and, theoretically, should 

 have been at its greatest brightness on that date, but comets usually 



oiliihit an inrronsi' in light as tboy npproaeli the sun and the present ( 

 one appeared fully as conspicuous during the thinl week of October \ , 

 as it did at any previous ilate. After traversing the constellations 

 Scorpio. Centaurus and Argo Navis, the comet will return northwards, 

 and, entering Cauis Major, will be visible at about the middle of 

 February in a position five degn^es S.K. of Sirius, when it will be a 

 little brighter than at the time of its discovery on September Ist. 

 Ob.scrvations of Ibis comet will be exceedingly numerous and extend 

 over a lengthy period. Many photographs of its aspect when nearest 

 to the earth in the early part of October will also be available for 

 discussion, in fact there will be an abundance of materials both for 

 the computation of the definitive orbit ard for the investigation of the 

 physical appearance and changes of the object. There i* every reason 

 to sup)xwe that the comet is moving cither in a parabola or in an 

 ellipse of great cxeeutrieity. 



Recent OB8KEV.iTrox3 of Meteobs.— Meteoric observers usually 

 have a busy time in July and .\ugust, but in 1902 the weather 

 conditions at many places prevented anything approaching a thorough 

 re-observation of the Perscids or of the multitude of minor showers 

 usually displayed at this productive epoch. Some fine meteors were 

 seen, while the Perseid system appears ti have exhibited normal 

 strength and to have given the usual evidence of the easterly motion 

 of its radiant. The following are a few of the positions determined 

 between .Tulv 27 and August 12: — 



At Brist:il observations were pursued between July 6-16, August 

 2 — 14, and August 25— September 7, and 260 meteors were seen. 

 The most active and sharply defined radiants were as under: — 



1902. o S 



July 6—9 ... 299 -f 2t 



JulV 6—13 ... 333-1-57 

 Aug. 24— Sept 7... 74 + 41 



Aug 26— Sept. 7 .. 337 + 8li 



Sept. 3—7 ... 118 + 83J 



Sept. 3—7 ... 30 + 3?" 



FIEEB.4LLS. —On October 15, at 7ii. 47m., a fine meteor equal in 

 brilliancy to Venus was seen by Mr. A. King at Newark, Notts. Its 

 aspect was starlike, colour pale green, and duration 'i^ or 3 seconds. 

 It moved slowly along a pith of il degrees, from 280'' — 8" lo 301° — 2"4''. 

 The same meteor wis observed by Mr. W. L-iscelles-Scott at Little 

 Ilford, Kssex, who gives the time as 7h. 52m., aud says that the object 

 camnienced its ilight at a point rather higher than midway betn*eeu 

 the horizon and zeuith in N.W. by X. It traversed a path of 105 

 degrees ending in S.W , and making an angle with the horizont^il 

 plane of 3U tlegrees. The meteor was also seen by Mr. 0. B. Holmes, 

 of St. Albans, who describes the path as nearly parallel with the 

 bright stars A'ega and Altair, and about 20 degrees to the west. 

 Combining the three observations, the approximate position of the 

 radiant is indieited at 150' -H 43°, and the height of the meteor from 

 62 to 54 miles. It had a long path of about 130 miles, extending 

 from over Usk, Monmouth, to the English Channel, and the velocity 

 was 37 miles per second. 



On October 20, Sh. I3m. , a meteor about as bright as Jupiter was 

 observed by the Rev. W. F. A. Ellison, of Dublin, with a path from 

 15"-^46° to 42° -1-28°, which it traversed in IJ seconds. 



THE FACE OF THE SKY FOR DECEMBER. 



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



The Sun. — On the 1st the sun rises at 7.44 and sets 

 at 3.63 ; on the 31st he rises at 8.8 and sets at 3.57. 

 Winter commences at 7 p.m. on thf i'Jnd, when the sun 

 enters the sign of Capricornus. 



Sunspots may now be expected, small grou])s of spots 

 having appeared from time to time of hit*.', 



