11-2 



KNOWLEDGE 



[June 1, 1900. 



the hemoglobin decomposes. A simple method is to allow the 

 blood to coa,t;ulate, express the serum, and separate the fibrin by 

 filtration. Through this solution pass a current of oxygen for 

 half-an-hour, and then carbonic acid gas for ten or fifteen 

 minntes. Crystals may be readily obtained from the blood of 

 the dog and other animals by adding alcohol in small quantities 

 during the passage of the gas currents. 



Sunlight is par excellence the best source of illumination 

 for photomicrography. A good substitute for a heliostadt is a 

 fair-sized mirror swinging on a double axis, and capable of being 

 regul.ated by hand. No difiiculty is experienced in keeping the 

 light centred, as ex]iosures by sunlight are of such short 

 duration. When using sunlight, care should be taken to ]>ass 

 the rays through a cell of saturated snlution of alum, in order 

 to absorb the he.at r.ays, otherwise serious damage may be done 

 to the ol^jective and the sub-stage condenser. 



After sunlight, diffused daylight from a window witli a 

 northern exposure is the next best light at the dispos;il of the 

 photo-microscopist, but when it is necessary to use artificial 

 illumination, acetylene gas or magnesium wire will be found to 

 give satisfactory results. Some objects are better shown under 

 a diffused light, such as may be obtained by the interposition of 

 a ground-glass screen, or near a window witliout the aid of a 

 condenser. If the colour of the object be dark, or reflects but 

 little light, the bull's eye should be tocussed on the S]iecinien, 

 care being taken to avoid glare or excess of illumination, wliich 

 will result in a confused image in the negative. With some 

 objects, the Lieber kuhn may be used advantageously, with 

 others the parabolic reflector, but the majority yield better 

 results under the most simple forms of illumination. 



Potato-agar is suggested as a good cultivating medium for 

 thermophilous bacteria. It is pre]iared as follows : — Potatoes 

 are steamed, peeled, and pounded. To 100 grammes of potato add 

 one litre of water, steam the mass for half an hour and then 

 filter. To the filtrate add two per cent, of agar and autoclave 

 the whole for fifteen minutes. It has been found advantageous 

 to add one per cent, of salt. After neutralization with soda, 

 and further steaming, filter the potato-agar into test tubes and 

 sterilize once more. 



To prepare photo-microgra])hs of diatoms, first photograph 

 the diatoms with a magnification of not more than 100 

 diameters, then enlarge so as to obtain a jihotograph of MO 

 diameters, proper for photo-printing. The finest details are 

 thus brought out, which otherwise are invisible to the eye in 

 the smaller photograph. Even forgeries in legal documents can 

 be discerned by using enlargement pictures, which microscopi- 

 cally are not visible if printed on bromide or velox paper. 



Magnesium as an illuminant for photo-micrography is not a 

 new idea. It was used for this purpose by Dr. R. L. Maddox 

 as far back as 1804, but owing to the expense of its production 

 it never became renlly popular. Magnesium is prepared com- 

 mercially from the melted chloride of electrolysis, or by 

 metallic sodium, and, when heated either in air or oxygen it 

 first glows and then burns with a bluish-white dazzling flame. 

 The experiments of Bun.sen and Iloscoe have shown that the 

 sun at its zenith has only 'M'rC) times more chemical brightness, 

 and :)^2i^^ times more visual brightness than magnesium. It is 

 therefore suitable in a special degree for photographic purposes, 

 and now that the price of the metal, either as bar, wire, ribbon, or 

 powder is so low, there is every inducement to the photo- 

 micrographer to call in its aid. 



The following method of jireparing sections of the teeth of 

 fish is suggested by Jlr. A. Underwood, of the Leicester Square 

 Dental Hospital. Sections of fishes' teeth should not be ground, 

 but the jaws and teeth should be decalcified in a 6 per cent, 

 solution of chromic acid, or a 10 jier cent, solution of hydrochloric 

 acid. After sections have been cut and stained, they should be 

 well washed in distilled water, dehydrated for three minutes 

 in absolute alcohol, cleared in oil of cloves, and mounted in 

 Canada balsam. Carmine is the best stain for fishes' teeth. 



In collecting any fleshy fungi, care should be taken to obtain 

 all the fleshy structure, as some of the most important characters 

 are only to be observed in the basal parts. To remove the basal 

 portion entire, a knife or small trowel should lie emplo\od. 

 Specimens that are broken off short with the ground are seldom 

 of much value for scientific purpo.ses. Fleshy ascomycetous 



fungi can best be jireserved in alcohol, but many of them may 

 also be satisfactorily dried. It is well, when fungi gathering, to 

 take a stock of tissue paper to wrap the specimens in. Each 

 form should be wrapped up separately so as to prevent breaking, 

 or soiling from contact with one another. 



A good dead black for varni.shing the inteiiur of microscope tubes 

 and cameras may be made l)v mixing two grains of lamp-black with 

 just enough gold size to liold the la.mp-ldack together. Add the 

 size drop by dro]) from a lead pencil. After the lamp-black and 

 size are tlioroughlv mixed and worked up, add twenty-four drops 

 of turpentine and worlc up again. 



To the oui'i'eni issue of tlie journal i»f I he Quekftt t'lul) .Mi'. A. 

 Earland <(iiitrilniles an interesting artirle on the structure, distri 

 hution and life history of the Radiolaria. illustrated by three plates 

 from the Report on the Radiolaria of the " Challenger " Expedition. 



[All communications in reference to this Column should be 

 (idilressed to }fr. J. 11. Coohe at the Office of Knowledge.] 



NOTES ON COMETS AND METEORS. 



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



Gl.\coiiiNi'.s Comet. — This object is now about 7 degrees south 

 of the star Beta .^lulromedae, and is moving to the north-west It is 

 rapidly becoming more favourably situated, and is aijproaching the 

 earth. The twilight is now, however, very strong, and the comet 

 being a faint one, a powerful telescope must necessarily be employed 

 in its observation. The comet will be presented under its best 

 aspect during the alisence of moonlight in tlie last half of .July. At 

 the middle of that montli the apparent brightness of the oljject 

 will be about twice that at discovery on January 31. In February 

 the comet >vas of the 13th magnitude, and described as a somewhat 

 difficult object on .account of its faintness by several of the observers 

 who were fortunate to obtain views of it. The following is an 

 ephemeris of the comet by A. Berberich (Ast. Nach. 3636) : — 



Distance iu 

 E. A. Dec. Millions of 



Date. h. m. s. " ' Miles. 



June 2 1 3 53 -H 28 36 ... 17-1 



„ 6 ... o 57 49 + 30 11 ... 167 



„ 10 ,.. EO 40 + 31 52 ... 161 



,, 14 .... 42 9-1- 33 39 ... 155 



„ 18 ... 31 .59 + 35 31 ... 148 



„ 22 ,.. 19 43 + 37 29 ... 140 



„ 26 ... 4 .50 -I- 39 31 ... 134 



., 3(1 ... 23 46 53 + 41 32 ... 128 



July 4 ... 23 25 11 + 43 27 ... 122 



CoMKT DiscovKRERS. — The close of the last century terminated 

 the interesting .and numerous series of conietary discoveries effected 

 by Miss C'aroUne Herschel, and by Messier and Mechain. But Pons 

 very sliortly afterwards came into the fielrl and eclipsed all the 

 efl'iats of las predecessors in this productive line of work. Originally 

 n .loor keeper at the observatory at Marseilles, the instruction 

 and encouragement he received from the director Thulis (discoverer 

 of Encke's Comet at its return in 1805), resulted in his taking up 

 the search for comets, and liis jierseverance and genius for the work 

 enabled liim to make a remarkaljle number of discoveries. Now, at 

 the close of the nineteentli century we liave m.any successful comet 

 Imnters, including Brooks. Swift, Perrine, and Ciacobini. Among 

 those wlio liave earned special distinctiort in this br.anch during the 

 last half of the century are Tempel, Winnecke, Donati, and 

 Klinkerfries, who have "gone over to the majority." Others in- 

 cluding Bainard, Borelly, Coggia, H. P. Tuttle and a few others 

 of less renown are still living though engaged in other astronomical 

 work. When the history of cometary discovery in the nineteenth 

 century ccjmes to be written due praise will be given to Pons, 

 Tempel, Brooks, Barnard, Swift, and Winnecke, who have proved 

 themselves the most successful workers in this .ittractive and ex- 

 citing field. 



The April Meteobs. — The weather was clear and the evening 

 sky moonless at the epoch of this shower, but it did not return in 

 any strengtli. Meteors generally were rare — a characteristic of the 

 Spring season — and the Lyrids only reappeared in sutficient numbers 

 to prove their existence. Prof. A. S. Herschel watched the sky at 

 Slough for short intervals on April 15. 16, 17 and 18, and during 

 an aggreg.de of 7 hours of fibservation only recorded 7 meteors. 

 On April 19 he saw 12 meteors in 4^ hours. On April 20, 25 meteors 

 in 5 hours, and on April 21, 35 meteors in 4^ hours. Tlie true 

 foiuetary Lyrids from a radiant at i7t)''-H32'' were in very weak 

 evidence, only 3 or 4 being seen, while about 12 were from a good 

 radiant at 277" -H 30". Outlying radiant.^ were in Draco and Lyra 

 at 261" + 48° and 280° + 47", comprising between them 15 or 20 fine 



