214 



KNOWLEDGE. 



[SEPTEirBER 1, 1900. 



Ht(ctoscopi). 



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



Thft following simple method for examining the gonococci of 

 purulent ophthalmia is suggested by Dr. W. li. Canfield. A little 

 of the pus is pressed between two fover glasses, which are then 

 drawn apart. The glasses are allowed to dry, and are cjuickly 

 passed through a Bunsen flame to coagulate the albumen and to 

 fix the pus. A few drops of the ordinary methylene blue or violet 

 are allowed to cover the specimen for a few minutes and washed 

 off, after which the specimen may be examined in water or 

 glycerine, or it may be dried and mounted in balsam, which makes 

 it more distinct. 



Permanent preparations of blood — amphibian for preference as 

 the red cells are so large and contain such prominent nuclei — may 

 be prepared by allowing fresh blood to fall drop by drop into <i 

 solution of osmic acid (two per cent, acid solution, one part ; one 

 per cent, solution of sodium chloride, two parts ; di.stilled water 

 one part). The solution should be constantly stirred while the 

 blood is dropping Allow tlie blood and acid to stand one night, 

 and then wash the acid away witli distilled water. Add alcohol, 

 then clove oil, in which the blood may be kept indefinitely. Before 

 tlie alcohol is added, the nucleus of the corpuscle may be stained 

 in alum carmine ; or the whole corpuscle may be stained in aniline 

 blue. Mount in balsam. 



A warm slide is an indispensable piece of apparatus to the student 

 of histology. In the study of ama>boid movements it is essential 

 unless a suitable spot in the frog's web can be found. To make a 

 warm stage, take a strip of copper the size of a glass slide, and 

 make a diaphragm opening in the centre. Attach a long strip of 

 c<jpper to this — or the wliole can be of one piece — sufficient to 

 pi'oject about four inches over the edge of the stage of the 

 microscope. The flame of an alcohol lamp heating the end of this 

 strip will, by conduction, heat the whole piece together with the 

 slide placed on it. A drop of blood being prepared for examination 

 in the usual way, make a ring round the cover glass with oil to 

 prevent evaporation, place on the warm stage, apply the heat, and 

 the leucocytes can be studied in their movements with higher 

 powers and with greater ease than in the frog's web. 



A water bath is another very necessaiy adjunct where a certain 

 very moderate degree of heat is not to be exceeded. Few persons 

 fully appreciate the difficulty of regulating or even estimating tl'.e 

 temperature of an object held over a naked flame, and mischief is 

 often done before the operator is aware of it. A serviceable watsr 

 bath is easily extemporized out of an old fruit can and a small 

 beaker glass. This serves for exposing material and preparations 

 to a temperature lower than that of boiling water. Where slides 

 are to be so heated, the simplest contrivance is a flat tin box, 

 w-itli all the joints (cover and all) tightly soldered. A small 

 tube closed with a cork serves to admit the water. 



Sections of buds may be cjuickly prepared for class demon- 

 stration by the following method. Fix the specimen in the section 

 cutter, wet it with alc-ihol, and slice off the sections, meanwhile 

 keeping the knife flooded with alcohol. Place the specimens in 

 alcohol tinged with iodine green, and leave them there for several 

 hours until the solution becomes colourless. Next place them in a 

 solution of alcohol and eosin, and leave them till they assume a 

 pink colour. Pass them through an alcohol bath, immerse in 

 clove oil for a few minutes, and mount in Canada balsam. 



The curriculum of the elementary school has recently undergone 

 a much needed and welcome reform. The new code contains, inter 

 alia, the official sanction of the Board of Education for the recog- 

 nition of nature study as a means of educating the childien of the 

 peojde. This is a step in the right direction, for when children 

 are early taught the nature study of evei-y-day life, and become 

 familiar with the common things in nature around them, their ideas 

 as to cause and effect in natural phenomena will cease to be asso- 

 ciated with superstition and mystery, and the range of available 

 information open to them will be indefinitely extended. No 

 educa,tion that does not inchide a knowledge of the every-day pheno- 

 mena of nature can be regardeil as complete : and as there is a veiy 

 wide range of the most essential and )iractical knowledge that can 

 lie reached only through the microscope, the day may perhaps be 

 not so far distant when the microscope, as an aid to nature study, 

 will be used more extensively and more seriously in our public 

 schools than it is at present. There is no reason whatever whv a 

 compound microscope of low magnifying power should not be just 

 as much a common aj)purtenance of a well regulated elementary 

 school as a blackboard or a piano. 



All who are interested in microscopy and photo-micrography 

 should obtain a copy of an interesting little brochure entitled 

 " (_)i thochroniatic Photography," which is being distributed gratis 

 l)y Messrs. Cadett and Neall, Ashstead, Surrey. 



We have recently had an opportunity of experimenting with the 

 " Absolutus " light filter used in conjunction with the Cadett Light- 



ning Spectrum plates. The great rapidity of these plates, the 

 sensitometer number of which was 360, renders them specially 

 suitable foT photographing the movements of microscopic plants 

 and animals, while their extreme sensitiveness to all colour lumi- 

 nosities of the spectrum, excepting a very small margin at the 

 extreme red end of the spectrum, enable them to represent with 

 great delicacy the gradations in the coloured luminosities of stained 

 jireparations" Tlie " Absolutus " light filter, which is specially 

 adjusted for the spectrum plate, i-enders all gradations correctly 

 with but a very small margin of error. It may be used eithei 

 before or behind the objective. Its use increases the exposure at 

 a window with a northern outlook about twenty times, but this 

 is really no drawback with the Lightning plate, as, owing to its 

 great rapidity, the exposure necessary is invariably shorter than 

 it would be when using an ordinary plate without a filter. The 

 surfaces of the " Absolutus " are optically worked, and the colouring 

 accurately adjusted by the help of Abney's colour sensitometer 

 to suit the spectrum plate. Workers with light filters know the 

 unsatisfactorj' nature of ordinary coloured glasses and fluid cells. 

 The care bestowed on the manufacture of the " Absolutus " 

 eliminates most of the objections, and, in addition, the colouring 

 of the screen is pleasant to the eye, and it does not interfere with 

 the definition of the image. 



[All communication!) in reference, to this Column -ihoiild be 

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



NOTES ON COMETS AND METEORS. 



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



Nkw Comet. — In justification of our statement in last month's 

 notes that it was highly probable we should shortly hear of a dis- 

 coveiy in this field, a bright comet with a tail was discovered by 

 Borelly at Marseilles, and by Brooks at Geneva, U.S.A., on the 

 night of July 23. The comet was moving rapidly northwards. 

 The position at discovery was given by Borelly as 2h. 43m. 40s., 

 Dec. -^ 12° :iO' in the extreme S.E. region of Aries. On the follow- 

 ing night the comet was observed by Bigourdan at Paris, and the 

 daily motion was found -t- 16' in E.A. and +'!'•' 48' in Dec. On 

 .July 30 it was seen at Bristol in a (>l inch refractor ; it was a con- 

 sjiicuous object with a bright tail, and in the beautifully cle.ar sky 

 which prevailed soon after midnight the comet was just perceptible 

 to the naked eye. 



tir.vcoBiNi's Comet. — This object has now become exceedingly 

 faint and is rapidly passing beyond the sphere of our observation. 

 Its place on Scptcndier 2 will be B.A. ITh. 39m. 7s., Dec. -h 17° 58'-3, 

 and its distance from the earth will be 169 millions of miles. The 

 aspect of the comet will be such that only the largest telescopes 

 will be able to deal effectively with it. 



De 'Vigo's Comet (1844 I.). — This object, which was computed 

 to revolve in a period of about 5^ years, was not redetected during 

 the half century whicli followed its discovery, but in August, 1834, 

 Mr. E. Swift, son of the famous and veteran comet finder Lewis 

 Swift, found a small periodical comet, the elements showing a 

 striking resemblance of orbit to that of De Vico's comet, and it 

 seemed probable that the two bodies were identical, allowing for 

 some slight differences of orbit introduced by planetary pertur- 

 bation. The return of the comet is now due, but the circumstances 

 are not very favourable. In Ast. Nach. 3653 Seares gives a 

 sweeping ephemeris, from which it appears that the object on 

 September 2 will be in K.A. 16h. 17m. 19s, Dec. S, 2.5" ."/'. This 

 position is less tlian 1" N.E. of the star o" Scorpii, tlic place of 

 whicli on January 1, 1901, is R.A. ]61i. Lira. 10s., Dec. S. 2.5" 21'. 

 The bright star Antares will be only 2 degrees E.S.E. of the comet 

 at the same time. The latter will be about 190 millions of miles 

 distant from the earth early in September, and far iieyond the 

 reach of ordinary telescopes. 



FiREn.ALLR. — In the strong twilight at 8h. 47s. on July 17 a 

 splendid fireball appeared over the north of England, and" left a 

 streak visible for more than three quarters of an hour. It moved 

 somewhat slowly from south to north, and the nucleus burst out 

 with great brilliancy several times, finally dividing into two frag- 

 ments. Dr. C. O'Hara, of Burnley, describes the meteor as falling at 

 an angle of about 45 degrees, and in a low altitude a little east 

 of north. \i Sjiennymoor, I3urham, its direction of flight was 

 noted from .50° over the S.E. horizon to 15" above N.X.E., and 

 duration 2^ or 3 sec. The same observer says the fireball con- 

 sisted of two pear sliaped masses, tailing off behind into two parallel 

 streaks of vivid white brilliancy accompanied by blue and crimson 

 coruscations. The writer has received about 15 accounts of the 

 meteor from various observers in the N. of England and Scotland. 

 The real path of the object appears to have been from a heignt 

 of 58 miles over Pickering, Yorks, to 15 miles over the North Sea. 

 Its length of observed path was 175 miles, and its astronomical 

 radiant point was at 249° — 20" a few degrees N.E. of Antares in 



