Jax. 30, 1885.] 



KNOWLEDGE 



77 



o ^ -.\xvVX wwv^v 



at; illustrated 



MAa^ZINE OF SCIENCE 



PLAINLYWORDED EXACTLY DESCRIBED 



LOaXDOX: FN WAV, J AX. W, 188.- 



Contents of No. 170. 



Pleasant Hours with the Micro- 

 scope. Bv H.J. Slack 77 



The Earth's Shape and Motions. 

 iJUut.) By K. A. Procter 7S 



An Electric Tram-Car. By. W. 

 Slineo 80 



Needed Star-SurreTS. By R. A. 

 Proctor SI 



Rambles with a nanuner. By W. 

 Jerome Harrison 83 



Chats on Geometrical Measurement. 

 By B. A. Proctor 8* 



Chapters on Modem Domestic 

 Economy 85 



PAGB 



How to Take Care of aTricycle. By 



John Bro\%'niDu 86 



Wuodcn Magnets to Cure Disease... 87 



Newton r. Descartes 87 



The Begiiiuing of Life, (itiua,) By 



H. A. Proctor 88 



Editorial Gossip 90 



Heviews : Legendsof the Algonquin 



Indians. Bv Hdnord Clodd HI 



Some Boots nii Our TaWe 92 



Face of the Sky. ByF.K.A.S 93 



Correspondence 9-t 



Our Inventors' Column 97 



Oar Chess Colomn 98 



PLEASANT HOURS WITH THE 



MICROSCOPE. 



By Henry J. Slack, F.G.S., F. 11 M.S. 



THE plan adopted iu these papers has been to luive the 

 objects described alway.s under view at the time of 

 writing, even when they were familiar to the writer. A 

 temporary interruption has lately caused delay, but the 

 present opportunity may be taken to reply to the wish for 

 some hints on mounting objects. The practised mounter will 

 only want an occasional mention of new methods, but the 

 beginner may be assisted by some elementary iustiuctions. 

 Of all the modes of mounting objects that require to have 

 their transparency increased and their tissues preserved 

 from change, that effected with the help of Canada balsam 

 is the most important, and the student should learn how to 

 apply it under different circumstances before he tries other 

 plans. Canada balsam is a sort of turpentine, and usually 

 sold by chemists and opticians in a perfectly clear 

 and clean state, about the thickness of stiffish glue. 

 This is too thick for a great many purposes, and it is 

 a good way to put about half the quantity in the usual 

 squat bottles in which it[is supplied, or say, a dessert-spoou- 

 ful into another wide-mouthed squat bottle, and pour over 

 it a teaspoonful of pure benzine, or benzole as it is some- 

 times called. This should be stirred in with a little ttick 

 or glass rod, and kept for a few hours in a warm place. If 

 the bottle is not placed too near a fiie, it may be corked, to 

 prevent evaporation, but it must not then be allowed to get 

 hot enough to risk its bursting. If the balsam is not found 

 to be about as thin as gum-water is usually prepared, a 

 little more benzine should be added. This requires care, 

 as when a certain degree of thinning is reached, further 

 additions of the solvent act with unexpected rapidity in 

 making the solution more fluid. If it is too thin, leaving 

 the cork out and placing it near the fire will soon make 

 it thicker again. The whole supply of balsam .should 

 never be thinned, as it is wanted in different states for 

 different objects. A good one to begin with is a wing of 

 any fly, like the house-fly, or of an insect not bigger than a 

 wasp or bee. A few hairs of a mouse, or rat, or hairy 

 caterpiUar will do very well, or a few diitd spiral vessels 

 pullel out of a rhubarb stalk. The reason for selecting 



some such object to begin with is that more delicate ones, 

 or thicker ones, require more skill and caie to avoid 

 spoiling them. Whatever may be selccttd of the sort ad- 

 \i.si'tl, iilace it in the ctntrc of a glass slide, and drop a very 

 little of the thinned balsam upon it. The operator should 

 keep a little stick, like a (lencil, cut to a point, for this 

 jmrpose. It will take up a minute droplet for small objects, 

 or a large drop for bigger ones, and should bo wiped clean 

 with a rag moistened with benzine when done with. 

 As soon as a drop of balsam is on the oVyect, a thin glass 

 cover should be superposed. If this is done gently, and 

 steadily, and accurately, so as not to require a further Uteral 

 movement to adjust it, the baltani will S])read evenly, 

 without air-bubbies. If the cover j^lass is large— say from 

 I in. to ; in. in diameter— it is sometimes well to let one 

 edge rest on the slide, and then allow it to fall gently on 

 the object. Tlu! operator should have at hand a few of the 

 little spring clips sold by opticians, and use one to press 

 the cover firmly down. Balsam thinned with benzoic, or 

 with another excellent solvent, wood naphtha — also called 

 pyroligneous ether and pyroxillic spirit -hardens readily by 

 evaporation of the solvent in a warm place, and if there is 

 no occasion for rapidity, it may be left for some hours in a 

 fender, or for a day or two iu a warm room. A quicker 

 method is to place the slide on a little table of sheetrbrass, 

 supported by four legs, and high enough to put a spirit- 

 lamp under. It is best to Hp]ily only a gentle heat, and the 

 lamp need not be directly under the slide, as the whole 

 brass platt^ soon gets hot. 



Balsam thinned with benzine will permit a quicker but 

 rather more risky treatment when the objects are small 

 and thin. As soon as the covering-glass is on and lightly 

 pressed down it may be held over a spirit-lamp and just 

 allowed to boil. It will then be full of small air-bubbles, 

 which should be instantly squeezed out by pressure with a 

 little stick. With practice this usually succeeds, and the 

 balsam is at once made quite hard ; but it is not advisable 

 to try it with a rare object, or one that cannot be easily 

 replaced. One danger is that the object may be driven out 

 of the centre, or too near the edge of the cover. Another 

 is that some air-bubbles may remain in an awkward place. 

 The writer has, however, hundreds of slides successfully 

 prepared in this way. 



Large objects should always be mounted by slower 

 methods, and professional mounters let them have, in some 

 cases, a long while to harden. Thick objects, such as legs 

 of bees, &c., want the balsam thicker. If they do not 

 readily absorb the balsam, a previous soaking in spirits of 

 turpentine is useful, and the balsam may be thinned with 

 that solvent instead of benzine. If the object is too thick 

 for the covering-glass to bo pressed close to the slide, n 

 shallow cell may be made by cutting a round or sfjuare hole 

 in a piece of tinfoil, or punching a ring of that material. 

 The tinfoil can be obtained of different thicknesses ; some 

 about as stout as an ordinary addre.ss-card is the handiest. 

 Thin sheet-zinc will also do, or a piece of card. Brass tings, 

 flattened do for some cells ; but Canada balsam gradually 

 acts upon them, and a green copper salt makes its appear- 

 ance. Glass cells are the best where a depth of l-20th or 

 more of an inch is required. 



Many oljects are injured by squeezing them too flat. 

 The mouth organs of bees, flies, &c., for example, can 

 scarcely be understood when superposed parts of their 

 structure are all flattened into the same plane. Mounting 

 in a shallow tinfoil cell is much better, and approaches the 

 merit of fluid-mounting without its disadvantages. Some- 

 times it is necessary to get water out of an object without 

 shrinking it by drying. The strongest alcohol will soon 

 remove most of the water, and then a little soaking in a 



