SCIENTIFIC NEAVS. 



[Jan. 27, iS 



exceedingly capacious, while a still further provision for 

 air is found in the form of a number of sacs, which occupy 

 the whole remaining cavity of the chest. These, being 

 constantly filled with heated air, naturally assist very 

 greatly in diminishing the weight, while the principal 

 bones, which are hollow, communicate directly with them, 

 and are filled with the same unsubstantial medium. This 

 latter fact has more than once been demonstrated in a 

 somewhat singular manner, a wounded bird, falling into 

 the water after sustaining a compound fracture of the 

 limb, having respired through the projecting bone while 

 its nostrils were submerged. 



Upon the marvellous structure of the feathers, which 

 add so greatly to the expanse of the wings and tail, 

 while increasing the weight in only an infinitesimal de- 

 gree, we need not enlarge, as they are not in themselves 

 necessary to flight. But we may mention the fact that in 

 a bird so comparatively weak in flight as the common 

 sparrow, the area of the extended wings amounts to 

 rather more than twelve square inches ; and the sparrow 

 weighs, when fuUy adult, only one ounce. Now, work- 

 ing out the calculation by rule-of-three, we find that a 

 twelve-stone man, at the same ratio, would require a 

 wing-area of no less than two hundred and twenty-four 

 square feet ; in other words, each wing must be twenty 

 feet in length by about five and a half in breadth. And 

 the strength of muscle necessary to work such wings 

 may be imagined, but could scarcely be attained. 



Finally, again, the position of a bird's body during 

 flight is parallel with the plane of the earth's surface. 



In the insects, in which we find flight in its utmQSt 

 perfection, the bodily structure is still more strangely 

 modified. But these we must consider in a subsequent 

 paper. 



( To be continued. ) 



HOW TO WORK WITH THE MICRO- 

 SCOPE, 



OUR modest hints, intended for absolute beginners, 

 will not enter into any kind of rivalry with the 

 large and elaborate books on the subject, from one of 

 which (Dr. Beale's) we borrow our title. We speak to 

 those who have just bought, or are just about to buy, 

 one of the cheap and excellent instruments now to be 

 had, and we wish to lead them a step or two along the 

 right road. 



It is not uncommon for the purchaser to bring away 

 with him half a dozen ready-mounted slides, such as the 

 proboscis of an insect, a micro-photograph of St. Paul's, 

 and the like. There is no objection to this way of show- 

 ing what the instrument can do, and bought slides 

 satisfy that boyish curiosity which is usually a powerful 

 though unconfessed motive with everyone who buys a 

 microscope simply of his own pleasure. But the first step 

 towards work has still to be taken. What shall it be ? 



We advise the beginner to procure the very simple 

 appliances named in the following instructions, and to 

 proceed as follows : — 



Take a lock of woo], cleanse it from grease by thorough 

 shaking in a small bottle with methylated ether, and cut 

 off about a dozen hairs to a length of a quarter of an inch. 

 Wet these with water in a small water-colour saucer. 

 Pick them out with a small brush and a mounted needle, 

 and arrange them m the centre of a clean glass slip. A 

 drop of water will be taken out with the hairs, and this 



need not be removed. Now take a clean glass-cover, in- 

 cline it over the hairs by resting one edge on the slip 

 and supporting the other with a mounted needle. Gently 

 lower it into its place, and the preparation is ready for 

 examination. Repeat the operation several times, till all 

 serious mistakes are avoided. The commonest mis- 

 takes are these : — i. Too much water is added 

 to the hairs, so that the cover slips about. 2. Too little 

 water is added, and the space is not filled. 3. Air- 

 bubbles cling to the hairs ; imperfect cleansing may be 

 the cause. It is easy to avoid bubbles if the hairs are 

 wetted with alcohol before mounting. 



When wool can be rapidly and successfully mounted 

 in water, go on to examine a leaf A hyacinth leaf is 

 good for practice, but any similar leaf will do. With a 

 razor or perfectly sharp penknife, notch the surface of the 

 leaf, take the cut edge between the blade and the thumb, 

 and strip off a bit of the thin, transparent epidermis or 

 outer layer of the leaf. The success of the operation 

 may be judged by the absence of green colour from the 

 epidermis. |When a fair strip is got (it need not be 

 large) place it in a little saucer of water, trim it with 

 scissors, transfer to a slip by a brush well wetted with 

 water, and mount as before. 



Next, buy a shilling razor, which must be kept per- 

 fectly sharp, and try to cut sections through the hj'acinth 

 leaf Hold the leaf vertically between finger and thumb, 

 and cut from left to right, holding the razor quite horizon- 

 tally. The blade must be kept wet with alcohol, poured 

 on in small quantity from time to time. Draw the blade 

 from side to side, so as to use nearly the whole length in 

 cutting a single section. If you try to cut straight across, 

 as bread is cut with a knife, you will crush the delicate 

 tissues. When a fair section is got, float it off with alco- 

 hol or water, applied with a brush, and proceed as before. 

 Remember that the section need not be large, but that it 

 must be really thin ; if it thins out to an edge, so much 

 the better. Cut plenty at a time, without being too 

 solicitous about every one, and then pick out the thin 

 ones. 



Six or seven evenings ought to bring a novice, not by 

 nature clumsy or untidy, to this point. He is now ready 

 to examine for himself a great variety of vegetable struc- 

 tures, or to study with advantage the fuller explanations 

 of practical books. But let him aim at simplicity in 

 everything. Having learnt to mount in water, or 

 glycerine and water, let him learn to mount in balsam, 

 and stick to these two methods till he has got some real 

 skill. When the time comes to use stains, take one 

 stain, say borax carmine, and try no other for a long 

 time. The common mistake is to have so many resources 

 that nothing ever succeeds as it should. 



Lastly, do not be too solicitous about preserving your 

 early attempts. They have no real value, and, if you get 

 on as you ought to do, you will laugh at them very soon. 

 The working microscopist in biology, for example, selects 

 very rigorously, and only preserves what is rare or un- 

 usually good. He is not thinking perpetually about his 

 cabinet, but about his studies — a very different thing ! 

 Aim not at a well-stocked cabinet, but at the power of 

 demonstrating, whenever required, all the details of a 

 new plant or animal. 



The Sun's Parallax. — The horizontal parallax of the 

 sun at its mean distance from the earth is now deter- 

 mined at 8", 808. 



