December 1, 1900.] 



KNOWLEDGE. 



2^5 



glass slip on a piece of stout cJinlboartl, dniw diagonal lines to 

 locate the centre, and then draw a series of squares and circles 

 about this centre ciinal to the diameters of the cover-glass most 

 used. This will be found iinite as s;itisfactory as the turn- 

 table for mounting purposes. 



Jajxnuese tissue paper used by dentists is excellent for wiping 

 and cleaning lenses, oculai-s, and objectives. 



To examine in the living state small freshwater alg;\;, protozoa, 

 small crustaceans, hydra, small worms, and other minute jilants 

 and animals, they must be mounted in some inert liquid, as 

 water : preferably a drop of the litiuid in which the organisms 

 live and grow. Their motion may be reduced by mounting in a 

 solution (10 per cent.) of gum arabic. 



Jlinute objects like diatoms and the scales of insects may be 

 arranged in geometrical figures or in some fanciful way, either 

 for ornament or more satisfactory study. To do this the cover- 

 glass is placed over a guide. The guide for geometrical figures 

 may be a uet-mierometer, or a series of concentric circles. In 

 order that the object^s may remain in place, however, they must 

 be fastened to the cover-glass. As an adhesive substance, liquid 

 gelatine thinned with an equal volume of 5i) per cent, acetic 

 acid answers well. A very thin coating of this is spread on the 

 cover, with a needle or in some other way, and allowed to dry. 

 The objects are then placed on the gelatinized side of the cover 

 and carefully got into position with a mechanical finger made 

 by fastening a cat's whisker to a penholder. After the objects 

 are arranged the operator breathes very gently on the cover- 

 glass to soften the gelatine. On drying the objects will be 

 firmly anchored. In mounting, one may use Canada balsam, or 

 mount in a dry cell. 



Shellac cement is a very useful medium for sealing prepara- 

 tions and for making shellac cells. It may be readily prepared 

 by half filling a bottle with scale or bleached shellac, and adding 

 thereto sufficient of '.to per cent, alcohol to fill the bottle. The 

 whole should be sh.aken occasionally, and allowed to stand until 

 a clear stratum of liquid appears on the top. This supernatant 

 liquid is then filtered through absorbent cotton into an open 

 dish or wide-mouthed bottle. To every .oO c.c. of this filtered 

 shellac, f) c.c. of castor oil and .j c.c. of Venetian turpentine are 

 added to render the shellac less brittle. The filtered shellac 

 will be too thin, and must be allowed to evaporate till it is of 

 the consistency of thin syrup. It is then put into a capped 

 bottle and is ready for use. 



The examination of living micro-organisms is, as a rule, best 

 carried out by means of the " hanging drop." For this purpose 

 a thick glass slide having a concave well in the middle is made 

 use of. The ''hanging drop" is made in the following manner: 

 Place a small drop of water on a clean cover-glass on the table. 

 The drop must be small enough so that it will not run if the 

 cover-glass is placed on edge. The organisms are then placed 

 in the water and a ring of vaseline is placed around the edge of 

 the well on the upper side of the concave slide, by means of a 

 brush or match stick. The .slide, with its ring of vaseline, is 

 then inverted over the cover-glass and gently pressed down. 

 The cover-glass now adheres to the slide, which is then inverted. 

 Care should be taken to see that the ring of vaseline is continuous 

 around the edge of the well. If such is the case no evaporation 

 of the drop of water can take place, and hence the hanging drop 

 can be examined at leisure and without the presence of annoying 

 curreDts in the liquid. 



A great variety of bacteria, moulds and yeasts can be obtained 

 by the student of bacteriology from the air. The following 

 simple procedure, suggested by Dr. F. Xory, will enable anyone 

 to grow these bacteria from the air, and thus obtain a variety 

 of organisms suitable for examination in the living condition 

 and for staining purposes. Place two or three .sound potatoes 

 and a knife in a vessel of water and boil for twenty minutes. 

 Ponr away the water, and, when cool, cut them in halves with 

 the sterilized knife, taking care to touch neither the blade nor 

 the potatoes with anything. Transfer the potatoes, cut side 

 uppermost, to a piece of paper, and leave them exposed for from 

 ten to thirty minutes. Then cover them with a glass tumbler, 

 and at the end of about forty-eight hours they will begin to 

 show one or more pinhead growths. These growths are due to 

 organisms, which, floating about in the air, have dropped on the 

 potatoes and have there found a soil congenial to their growth. 

 The germination of seeds in sterilized water to which varying 

 quantities of oxygen liad been added has been studied by M. P. 



JIaze. lie concludes that, while life appears to remain latent, 

 certain slow changes take place, although germination under 

 water may fail on account of lack of aeration. Some small 

 seeds are developed slowly by the atmosphere within their 

 coats. Starchy seeds under water quickly lose all jmwer of 

 germinating, oily seeds retain it longer ; l)ut there is no proof 

 that any seeds can long retain their vitality. The weakening 

 of the submerged embryos is attributed to the accumulation of 

 poisonous products, especially aldehyde. 



Messrs. 11. and J. Beck have ]ilaced on the market a new 

 microscope on the " Continental ' model which they call the 

 " London." Many im])rovenients have been introduced in 

 matters of detail "which make it worthy of notice. The work- 

 manship is in Messrs. Beck's best style, and the price reasonable 

 for a first-class instrument. 



NOTES ON COMETS AND METEORS. 



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



Bkorsen's Comkt. — The ivtiirn of this interesting short-poi-iud 

 comet is expeded rarly in ItOl, and ii sweeping epliemeris lias boon 

 pul>li.slii'(l in Axt. Nm'h.. '.Wii), by .V. lierbcricli, of Bci-lin. From this 

 i( appears tlial tlio comet is now iiirisible in English skios owing to 

 its siiutborn declination, but thatil is travelling northwards and ought 

 to bo fdvovirably ]iresoiited to view at the end of January and in 

 Kebiuary, 1!K)1. JJerberich's epliemeris is for Berlin midnight, and 

 tlie positiims at eight day intervals are; — 



Dintauce of Comot 

 D:ite. K.A. Dec. in Millions of 



H. M. " ' Miles. 



190(1. DiTcmber 17 ... '.i2 S -41- 32 ... G2 



L'.j 21 u!) -39 Ki ... 56 



191M. Januarv 2 21 39 -33 4 ... 47 



" :u . 21 9 -22 .51.. ... 40 

 18 ... 20 8 , - 9 37 38 



Tlie patli is from Grns tlirongli I'iseis .Aiistialis and Capricornus, 

 afler wliich it passes tlirougb Aqiiila. It will ht- nearest to the earth 

 at tlie middle of .January, but at that time will be too near the sun 

 for observation. Soon af(erwards tlie eomet ought to become visible 

 iust before sunrise low in due east. This eomet was discovered in 

 1846, and it has a period of revolution of a'^out 5i years. Ttwas last 

 seen in 1879, and should have returned in 1884, 1890, and 1895, but 

 escaped deteetion. It is now questionable whether the comet exists 

 in the same form and dimensions as in 1879 and |irevioiis years. Tlie 

 supposition is tliat, bke Biela's double comet, it is )irai-tirally lost to 

 us as an observable object But it remains to be seen whelher the 

 large telescopes of the present day are capable of rcdetecting the 

 comet, for they will sure to be employed in the seareli during tlie 

 months of January and February next. 



Comet Borbelly-Bkooks. — This object is now exceedingly faint, 

 but its position is very favouralile. It, was observed by Dr. 8eliorr at 

 Hamburg on October lliUi, and may possibly be picked up in Decem- 

 ber in a good instrument. The following places are by Wedemeyer 

 (A.sl Xac/i., 3070) :— 



l^phemeris for ISerlin Midni<ilit. 



Distance in 

 Date. R-A. rX'c. Millions of 



liKMl. H. • M. s. o ' " MilfS. 



December 10 ... Hi 19 17 ... +71 oL' .'56 ... ilo 



11, 16 26 5t ... + 73 30 ... 181 



18 .. 16 34 .J5 .. -I- 7t 12 34 ... 184 



22 .. 16 43 2.5 . +75 28 45 ... 187 



26 ... 16 52 33 ... + 76 48 38 ... 190 



Jani'in'ry 6 ... 17 23 15 ... + 80 13 (i ... 198 

 The comet is thus moving slowly to N.N.H. ani<ingst. tlie stars iu Ursa 

 Minor. 



Barvard's Comet (1884 II.).— This .>bject escaped observation at 

 its last two returns, and there seems a very meagre prospect of it being 

 ,sjcn at the present time owing to generally unfavourable conditions. 

 Its computed position on December 2nd is K.iV. 20h. 14m., Dec. 

 -21" ->'. 



Fiki-:bali, of S0.vn.iv, Octohke 21, 8h. 35.m. -A magnificent 

 slow-moving fireball w.as observed from all parts of England. Thi' 

 sky was clear over tlie country, .and as the metejr travelled leisurely 

 along its coui so from S.W. to N.E. there occurred three explosions 

 or outbursts, and these induced very vivid lightuinglike Hashes. At 

 Tewkesbury the meteor is said to have given a momentary Hood of 

 brilliant moonlight, and about three minutes later there was a detona- 

 tion like that pr.jdueeil by the firing of a heavy gun at a great distance. 



