70 



KNOWLEDGE 



[Makch 1, 1900. 



Microscopists, both at home and abroad, will hail with satis- 

 faction the resolutions that have recently been adopted by the 

 Council of the Royal Microscopical Society to standardize the 

 Tarious parts of the microscope and its accessories. A beginning 

 has already been made, for the details of which we are indebted 

 to the courtesy of the Council. The standards adopted in 1S82 

 have been withdrawn, and the size for the inside diameter of 

 the sub-stage fitting has been fixed at l'b'27 inches (38'786 mm.). 

 The gauges for standardizing eye-pieces will, in future, be the 

 internal diameter of the draw-tubes ; the tightness of the fit 

 being left to the discretion of the manufacturers. Four sizes 

 of the intern.al diameters of the draw-tubes have been fixed as 

 follows :~No. 1, 9173 inch (23-300 mm.). This is the Con- 

 tinental gauge. No. '-', 1'04 inches (26'4iri mm.), is the mean of 

 the sizes used by the English trade for students and small 

 microscopes. Xo. 3, 1'27 inches (32'258 mm.), is the mean of 

 the sizes used for medium-sized binoculars and other microscopes 

 . of a similar class. No. 4, 1-41 inches (3;r814 mm ), is the 

 maximum size for long- tube binoculars. The sub-stage gauge 

 is that which has been used by the English trade for many years 

 past, the variation among difEerent makers being not more than 

 a few thousandths of an inch. We hope to be able shortly to 

 give the standard gauges of the eye-piece cap and of other 

 apparatus. The plugs and ring gauges of all of the above may 

 be inspected bj* the puljlic at the Society's rooms. 



With all the diversity of interesting lines of research that are 

 offered to the student of botany to-day, there is none more 

 inviting to a student, or better adapted to bring into activity 

 all the I'esources of his judgment, than the systematic study of 

 the species of some limited group, provided this is properly 

 combined with a study of the morphology, development, and 

 ecologic relations of such a related series. The Fungi and 

 Mycetozoa offer themselves, in a special degree, as a field for 

 thorough and oi'iginal systematic study, and students of these 

 groups will therefore be glad to hear that Professor Lucian 

 Underwood, of Columbia University, has .just issued, in book 

 form, an admirable exposition bearing on the moulds, mildews 

 and mushrooms. 



A simple and effective method for removing air bubbles from 

 microscopic mounts is suggested l)y P. S. Proctor in the 

 Pharmiireiitlcal Journul. A small syringe, having a glass 

 barrel, vulcanite mounts, and leather packing to the piston, is 

 the only apparatus required. Select one that is as nearly as 

 possible air tight, unscrew the top and remove the piston. 

 Close the nozzle with a small piece of beeswax, half fill the 

 barrel with distilled water, and into this drop the section or 

 tissues to be treated. Replace the piston and screw on the top. 

 The syringe being inverted and the plug of wax removed, the 

 air is driven out of the barrel by raising the piston till the water 

 begins to flow out of the nozzle, after which close the aperture 

 with the finger and lower the piston. A partial vacuum is thus 

 formed, and the air rapidly escapes from the cells of the tissue, 

 collecting in the point of the .syringe. By removing the finger 

 and raising the piston the lilierated air is forced out : this may 

 be repeated several times as long as air is being expelled from 

 the material. The same mode of operating is applicable to 

 objects that are to be mounted in Canada balsam if oil of 

 turpentine be used instead of water, and if the objects to be 

 mounted are quite dry before immersion in the turpentine. 



[All commtiii/catioim in rfference to thin Column should be 

 (idilri'sxed to Mr. J. II. Coohf. at the Office, of Knowlehgi:.] 



NOTES ON COMETS AND METEORS. 



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



New Comet. — The announcement has just been made (,l,s7. 

 \(irh. 3()1S) that Giacobini at Nice discovered a new comet on 

 .January Sl'st in R.A. 44" 2iV, Dec. 9" .06' south. The position 

 of the object was therefore between the stars i) and ^ Eridani. 

 The comet is moving slowly to the north-west. 



During the last few months the firmament has apparently 

 been free of comets visible in small telescopes. We have 

 now, however, approached a season when clearer skies and more 

 genial weather arc likely to encourage the search for these 

 bodies. 



PERioniCAL Comets. — These form a singularly interesting 

 class, in which we have witnessed a rapid increase of numbers 

 in recent years. The comets of short period, belonging to 

 the Jovian group, revolving in times varying from 3'3 to 

 about 9 years, now include about thirty members, though only 

 half of these have received satisfactory verification by having 

 been detected at two or more returns to perihelion. The 

 following is a list of the approximate dates of expected returns 

 of these bodies during the few ensuing years : — 



Comet. 



De Vico-Swift 

 Barnard (1884) 

 Brorsen 

 Denning (1894) 

 Encke 



Brooks (1S8G) 

 Swift (1895) 

 Tempel-Swift 

 Perrine (1896) 

 Spitaler (1890) 

 Faye 



Brooks (1889) 

 Pons-Winnecke 

 D' Arrest 

 Encke 

 Tempel (1873) 



The January Meteors. — Prof. Herschel, whose important 

 observation of the Quadrantids on January 2nd has been already 

 referred to (Knowi.ehoe, February, 1900), has thoroughly 

 reduced his results, and finds that several showers were actively 

 and distinctly visible on the night mentioned. The special 

 shower of Quadrantids formed about one-third of the total 

 number (80) of meteors registered. The various radiants 

 determined were : — 



The chief dis])lay of the epoch in Quadrans is generally of 

 very short duration, but it seems to have been unusually pro- 

 longed and conspicuous this year. The meteors were, however, 

 most .abundant on the morning of January 3rd. An observer 

 at Chalfont, in Buckinghamshire, says that between 6h. and 

 6h. 30m. a.m. on the date given there were several fine .shooting 

 stars which "had tails and burst like rockets." On the morning 

 of January 4th there were also many meteors. Mr. Robert 

 Service, of Dumfries, reports that he started for a drive at 

 6 a.m., and between that hour and daylight he counted moi-e 

 than thirty very fine meteors, hardly one being under 1st mag- 

 nitude. The prevailing colour was yellow. One brilliant 

 meteor descended through Leo and, after bursting, left a streak 

 which remained visible for quite a minute. Something of the 

 display was also seen in the evening of January 2nd by Mr. 

 J. H. Bridger, at Farnborougli, and Sir. T. H. Astbury, at 

 V/allingford, and two Quadrantids appearing at 6h. 20m. and 

 6h. 41m. were observed at both stations. 



Of fifteen meteors mapped by Prof. Herschel on the nights 

 of January 24th, 25th and 27th, several pretty bright, slow 

 ones indicated a r.adiant in the extreme south-west region of 

 Camelopardalus at about 43° + 63°. One of the meteors which 

 a]ipeared on January 25th, lib. 10m., was fortunately also 

 recorded by Mr. J. H. Bridger, at Faruborough, and a com- 

 parison of the two observations leads to the following results : — 



Height at beginning, sixty-five miles, over a point two miles 

 south-east of Atherstone, Warwick. 



Height at ending, forty-four miles, five miles north of Rugby. 



Length of observed path, twenty-six miles. 



Velocity, thirteen miles per second. 



Earth point, four miles north-west of Olney, Bucks. 



Eadiant point, 45° -1- 62". 



The shower is apparently the same as G.C. XLVII., with a 

 mean position at 50"-4 + C2°-9. 



