May 1, 1900.] 



KNOWLEDGE 



117 



tance. The int-erval of timo between the instant at 

 impact and the fomi of the splasli shown in the fifth 



(3) (6) 



Splash produced by a polished stone ball, 32 em. in diameter, when 

 falling iutp a basin of milk and water, from si heiglit. of 14 em. 

 Starting from the in.^^tant at which the sphere touched the surface 

 of the liquid, the intervals of time that have elapsed, in fractions of 

 a second, are as follows : — ■ 



(1) t = 0. The ball has just reached tlie liquid. 



(2) t = •0025 sec. Sheath of liquid bc^dnning to rise. 



(3) t = -0080 sec. Ball already covered. 



(4) t = 0110 sec. Shows the effect of polishing the left side only, 



leaving the right side rough. 



(5) t =' '0134 sec. Regularity restored by complete polishing. 



(6) t = '0243 see. Column resulting from converging streams of 



liquid. 



photograph when the sphere is completely covered was 

 a little under one-seventy-fourth of a second. 



The mechanics of the phenomena to which special 

 attention has been thus briefly referred is a subject of 

 too abstruse a nature to be gone into here, but the 

 interested reader who wishes to become more intimately 

 acquainted with these particularly interesting researches 

 should make a point of studying the papers under Prof. 

 Worthington's name in the Royal Society's " Proceed- 

 ings ' and " Transactions." The illustrations here re- 

 produced show that the commonest occurrences may be 

 made fruitful subjects of scientific analysis. 



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



Dr. H. C. Sorby, f.b.s., contributes to the current is.sue of the 

 Journal of the Royal Microscopical Socieli/ a paper on " The 

 Preparation of ilarine Worms as Microscopical Objects.'' With 

 a view to preserving the minute blood vessels of Xerc/s from 

 decomposition, the author experimented with many reagents, 

 but rejected all of them in favour of glycerine. His method is, 

 briefly, as follows : — Specimens measuring from two to three 

 inches in length were killed by jilacing them in strong glycerine 



diluted with an cr|Ual volume of water, and were afterwards 

 immersed in fresh water for ton miiuites to eliniinato tlio 

 glycerine. They were then arranged on a microscope slide, and 

 dried quickly in the open air at the ordinary temperature. A 

 cell built of glass slips was attached to a .slide, and the specimens 

 were mounted in balsam and protected by a thin cover glass in 

 the usual way. Dr. Sorby has specimens that were treated thus 

 two years ago, and they not only show no signs of change, but 

 the structure of tlie animal is more clearly defined in the 

 preserved state than it is when the animal is alive or recently 

 dead. 



At a demonstration recently given before the Royal Jlicro- 

 scopical Society of Londou, Dr. Spitta exhibited some very fine 

 micro-jihotographic work which he had done with lenses by 

 Zeiss, Powell, Reck, and Wr.ay. He spoke very highly of the 

 one-eighth apochromatic N.A. l'4()by Zeiss, which he considers 

 to be "the linest lens in the world" for micro-photography. 



Mr. W. Colquhon has been e.\pcrimcnting with staining 

 processes for the |)urpose of differentiating the canalieuli in 

 iione. None of the usual methods gave satisfactory results, for 

 though the nuclei of the bone corpuscles were stained, the out- 

 lines of the canalieuli were only faintly shown. Glass tubing 

 was, therefore, arranged in lengths of twelve feet on a wall, and 

 a bone with the head sawn off, the medullary cavity cleaned 

 out and one end corked, was connected with the glass tube by 

 means of a wide rubber tube. The periosteum was removed, 

 and any holes visible on the out.side were plugged with wooden 

 pegs. The tuliing was then tilled the whole length with stain, 

 to which a little antiseptic had been added. The bone being in 

 a dry room, dried, and as this occurred the stain was drawn in 

 to take the place of the evaporated moisture. After about a 

 month all of the nuclei of the bone cells were found stained, 

 and also the lining membranes of the canals. The bone matrix 

 remained unstained, but the canalieuli were faintly outlined. 



The new section of " Laboratory Photography,'' which has 

 recently been included in the Journal of Applied Micntucn/ii/^ 

 is both interesting and useful. Among many articles bearing 

 on the methods and technique of microscopy is a suggestive 

 paper on " Practicable Photo-micrography," by Mr. C. Potter, 

 and a note by Mr. W. K. Britton on " The Ray Filter in 

 Laboratory Photography." 



An electric microscope lamj) has recently been placed on the 

 market by Messrs. J. Swift & Son. It was designed by Mr. 

 J. E. Barnard to give an evenly illuminated ineld in the micro- 

 scope, without the image of the filament of the incandescent 

 lamp being thrown up from the mirror in the field of view. 

 This is effected by a light from the incandescent filament falling 

 upon a flat plane placed at an angle of 46° to the axis of the 

 lamp, and the surface of which is covered with a preparation 

 which throws off an intensely white light in such volume that 

 the largest mirror of any microscope can be fully illuminated. 

 The lamp is mounted on a swivel, enabling it to be placed at 

 any angle* and can also be lowered or raised at will. 



The focussing of a microscojiic object on a ground glass screen 

 requires much skill and care. The screen which is supplied 

 with the ordinary camera is generally too coarse, and in high 

 power photo-micrography even the finest ground glass obtainable 

 does not always give satisfactory results. For critical and 

 medium work it is essential that the focussing screen should be, 

 as far as possible, without gi-ain. A simple way of preparing 

 such a screen is as follows: — Take an unexposed photographic 

 dry plate and immerse it in a solution of chloride of barium for 

 ten minutes. Transfer it to a bath of dilute sulphuric acid 

 and gently rock the solution to and fro until a fine, even pre- 

 cipitate of b.arium sulphate has been deposited. Wash and dry 

 the plate, and it will be ready for use. 



Another method, recommended by Prof. Gage and others, is 

 to find the centre of the ground glass screen and then to place 

 a large circular or square cover-glass on it with Canada balsam. 

 To do this, warm the ground glass carefully, add a drop of rather 

 thick balsam to the centre on the ground side, and then apply 

 the cover and ])ress it down firmly. Put it away on a warm 

 shelf for a few days to harden, after which the excess of baLsam 

 may be removed from the edges with the aid of a penknife and 

 xylen or alcohol. The l)al.sam will fill up the inequalities in the 

 glass, and being of about the same refractive power will make this 

 part of the glass clear as if it were unground. The focussing 



