262 



KNOWLEDGE. 



[No%-EMBER 1, 1900. 



By John H. Cooke, f.l.s., f.g.s. 



It frequently happens that the objects for which the micro- 

 scopist is searching are mixed with coarser materials, from which 

 it is necessary to separate them. As a rule judicious washing 

 will effect the purpose, but sometimes it is necessary to resort 

 to burning or to the action of chemical reagents. Guano and 

 various organic matters are cases in point which yield interesting 

 residues after everjthing soluble has been washed away, and 

 everything combustible has been burnt either with fire or with 

 nitric acid. The siliceous cuticles of plants, too, may be pro- 

 cured by destroying all the other parts by chemical means. 

 An effective way is to heat the specimens in nitric acid, and 

 add slowly and very cautiously a small quantity of powdered 

 chlorate of potash. This operation needs great care, and the 

 face and hands should be protected from the spluttering of 

 the boiling acid. 



Considerable confusion exists as to the proper nomenclature 

 of photograyjhy with the microscope. In Germany and France 

 the term micro-photography is very common, while in English 

 photo-micrography and micro-photography mean very diSerent 

 thing.s. Thus : a pJioto-mici-' ir/ n/j/h is a photograph of a small 

 or microscopic object, usually made with a microscope and of 

 sufficient size for observation with the unaided eye : whUe a 

 iD/cro-i^hotograjili is a small or microscopic photograph of an 

 object, tisually a large object, like a man or a building, and is 

 designed to be looked at with a microscope. 



Collodion stained with aurantia makes a useful colour screen. 

 Dr. Learning, when preparing the negatives for the plates of 

 AVilson and Starr's atlases, made his colour screens by staining 

 a lantern plate, from which all the silver salts had been removed, 

 with an alcoholic solution of tropseolin. and then, after drying, 

 Canada balsam and a cover-glats were applied. 



When a carmine stain is to be used the restilts may be 

 obtained quicker by heating the stain. Place the watch-glass 

 containing the stain on a wire netting over the opening of 

 a water bath. As the water boils the heat of the steam wUl 

 cause the stain to penetrate more rapidly, with the result that 

 the details of the specimen are brought out more sharply. 

 These results may be obtained only with tissue which has been 

 previously hardened. Those hardened in a solution of chromate 

 of potash to which a few drops of chromic acid have been added 

 give the best results. 



Of the many mounting mediums miscible in water which are 

 used by the microscopist the most generally useful is glycerine. 

 It is necessary that it should be pure, and to be quite sure that 

 aU foreign matters such as dust particles are eliminated, it 

 should be filtered through filter paper or absorbent cotton before 

 being used. For preparing objects for final mounting, glycerine 

 and svater mixed in equal quantities forms a good mixture. For 

 many ])nrposes the final mounting in glycerine is made in an 

 acid medium, viz., glycerine 09 c.c, glacial acetic acid 1 c.c. By 

 extreme care in mounting, and by occasionally adding a fresh 

 coat to the sealing of the cover-glass, glycerine preparations last 

 a long time. They are liaVjle to be very disappointing, however. 

 In mounting in glycerine care should be taken to avoid air- 

 bubbles, as they are difficult to get rid of. A specimen need 

 not be discarded, however, unless the air-bubbles are large and 

 numerous. 



We have pleastire in calling the attention of microscopical 

 societies to the list of lectures which has been arranged for 

 delivery by members of the Extension section of the Manchester 

 Microscopical Society during the coming winter. The lectures 

 and demonstrations treat of every jihase of microscojjy, and are 

 given gratuitously to any society that may- care to apply for 

 them. Applications may be made to the Hon. Secretary, 

 S*!, Brookland Street, Eccles New Boad, Manchester. 



Ink for writing on glass may be prepared bj- dissolving 20 

 grains of brown shellac in l.'j'i c.c. of alcohol iu the cold, then 

 adding, a drop at a time, a solution consisting of 'do grains of 

 brjrax dissolved in 2,vit c.c. of distilled water. If this precipitates 

 the shellac add more .-xlcohol. allowing the excess to evaporate 

 afterwards, or warm the solution until the precipitate disappears. 

 One gramme of methylene blue may be used to colour the ink. 



The following easy and efficient method of preparing nucleated 

 blood for class use has been adopted in the histological labora- 

 tory at Cornell University. A few drojis of the fresh blood of 

 a necturus are put in a solution of osmic acid (1 per cent.) and 

 allowed to stand for fifteen minutes. The corpuscles by this 

 time are fixed and have settled to the bottom, and the fixer can 

 now be decanted ofE. After washing in water the blood is 

 carried on through the various grades of alcohol, stained with 

 paracarmine, dehydrated, cleared, and, as a final step, Canada 

 balsam is added sufficient to procure the proper dilution of the 

 cori)uscles. A drop of the balsam is then put on a slide, covered 

 with a cover-glass, and is then ready for use. 



Mr. E. L. Fullmer, of Ohio State University, has had consider- 

 able experience in mounting small Coleoptera and other small 

 insects, and in the ]jages of the Journal of Applied Microscopy 

 he briefly describes the more successful of his methods. That 

 which gives the best results for general work is as follows : drop 

 the specimens into absolute alcohol, and leave for an hour or 

 more to dehydrate, transfer to xylol for a few minutes to clear, 

 and mount in balsam. To make opaque objects transparent, 

 boil in caustic pota.sh for a moment, and then treat as above 

 described. In working with scale insects, the insects are first 

 picked out of the scales and placed upon a slide where it is 

 desired to mount them. A few drops of a five per cent, solution 

 of caustic potash are applied, and the specimens boiled in this 

 for two or three minutes by holding them over a bunsen flame, 

 after which proceed as above. 



\^All communications in reference to this Column should be 

 addressed to Mr. J. H. Cooke at the Office of Knowledge.] 



NOTES ON COMETS AND METEORS. 



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



Bobbellt-Bbooks's Comet. — This comet is now exceedingly faint, 

 the brightness on Iiovember Ist being only 03, as compared with 1 

 at the time of discovi'ry. Its position is degrees east of x Draeonis 

 at the beginning of November, and the comet is travelling very slowly 

 in an easterly direction. 



Pebiodical Comets. — Barnard's Comet (1884 II.) and De Tico- 

 E. Swift's Comet (1844-1894) are possibly visible in very powerful 

 telescopes, but the conditions are not favourable. Xo announcement 

 has been made at the time of writing that either of these objects has 

 been redetected iu the large instruments which are doubtless being 

 employed for the purpose. Amateurs provided with ordinary 

 telescopes must wait for future returns when these comets v\iU be 

 better presented. In Ast. Nach., 3664, Mr. F. H. Seares gives a 

 continuation of his finding ephemeris for De Vico-Swift's Comet, 

 and from this we extract the following : — 



Distance in 

 Date. E.A. Dec. Millions of 



H. M. s. o ■ Miles, 



^'ovember 16 ... 18 44 b7 ... 25 48 S. ... 2;^4 

 28 . . 19 16 12 ... 24 54 S. ... 227 

 December 14 ... 19 59 39 ... 23 2 S. ... 231 

 The perihelion passage will take place on February 13th, 1901, but 

 the comet will be too near the sun for it to be observed. 



FiBEEAXi OF September 2, 6n. 54m. — About 35 accounts of this 

 brilliant object were received, but they were not very definite as regards 

 the particulars of the phenomenon. Some of the descriptions have, 

 however, afforded a satisfactory means of comparison. Adopting the 

 ^ Cepheid radiant at 334° + 57° as best representing the observations, 

 it appears that the meteor became visible at a height of 85 miles over 

 Richmond, Yorts., and ended at a height of 20 miles over a point 

 near Fleetwood, Lancashire. Its length of observed course was 84 

 mUes. It was certainly one of the largest and most brtUiant meteors 

 seen during the year. Its sun-lit streak remained visible for more 

 than half-an-hour, and formed one of the most striking features of the 

 event. It is remarkable to find that the discordances among the 

 various observers are very great in regard to many of the details. 

 Three of the observers give the time as about 6 p.m., while another 

 mentions 6.15 p.m. Five others give the foUowing times, 7h. Cm., 

 7b. 15m., 7h. 20m., 7h 30m., 7h. 30m. Yet it is certain from the 

 rough descriptions of the path that only one meteor was observed and 

 that the correct time was as nearly as possible 6h. o4m. With regard 

 to the streak or train left in the meteor's wake, several correspondents 

 say there was none whatever visible. Three state that there was a 

 tail which ri'niained in sight about 5 miniUes, several give the time 

 of its dui-dtion as 10 minutes, two others watched it for .30 minutes, 

 while at Wetherby it remained in view imtU 7h. 30m., or 36 minutes 

 after the meteor flashed across the skv. Some of the observers were 



