August, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



213 



four inches. The sloping rests for the hands might 

 be about two inches high at the lowest ends and four 

 inches at the highest, but these measurements should be 

 governed by the size of the mirror, which must have 

 ample room in which to swing. The mirror itself 

 is a simple round penny mirror, such as can be boug'ht 

 at almost any toy shop, the larger the better. It is 

 deprived of its metal cover and let into a piece of wood, 

 which swings on wooden or metal pivots between the 

 two centre uprights of the stand. The simplest way in 

 which to make the support for the mirror is to care- 

 fully cut a hole of the proper size in a piece of stout 

 fret-wood, and to back it with another piece of 

 fret-wood, glueing the two together acd mounting 

 them on a cross beam, the projecting ends of which 

 are carefully shaped circular and fit fairly tightly into 

 corresponding holes. This piece of wood could also 

 be hinged to the bottom of the stand, but in that case 

 the mirror would not remain central when tilted at an 

 angle. A little more skill would be required to arrange 

 universal movements, but they are really not neces- 

 sary. The stage is a piece of plate glass, 5 by 4 inches, 

 ground at the edges, and can be ordered from anv glass 

 shop for a shilling or so. It lifts out if necessary. Two 

 pieces of cardboard of the same size should be cut to 

 go underneath when required; both should be covered 

 on one side with black and the other side with w'hite 

 paper, and one should have a hole about li inches in 

 diameter in the centre. The whole stand might be 

 made of wood § inch thick, mahogany or walnut being 

 preferable to pine, and the dove-tailing or grooving 

 should be done and finished off r.s carefully as possible. 



The holder for the lenses can be made, as illustrated, 

 by fitting a piece of J-inch brass tube about eight inches 

 high into a small stand about 2i or three inches in 

 diameter. A piece of springy ^-inch brass wire is then 

 rolled several times round the upright, as shown; one 

 end is turned up about three inches away from the 

 stand, and the other end is shaped intO' a ring to hold 

 a watchmaker's eye-glass. Tliis last can be bought 

 anywhere for about lod. or a is., and makes a most 

 useful dissecting lens. On the turned-up end can be 

 put an ordinary pocket magnifier in ebonite mount, 

 such as can be bought for a shilling and upwards, 

 according to the number of lenses. 



This stand, simple as it is, will be found a useful and 

 errcienl piece of apparatus. It will be money well 

 spent if the worker provides himself, however, with one 

 of the beautiful aplanatic lenses sold by all the principal 

 opticians. They give exquisite definition, together with 

 a flat field, and being much less tiring to the eyes are 

 excellent for dissecting, and are also the most perfect 

 ol those magnifiers which the real microscopist can 

 always bring forth from his pocket when wanted. The 

 most useful powers do not exceed ten diameters, and 

 a lower power gives a larger field and greater working 

 distance. Perhaps six is the most useful and convenient 

 magnification. 



Botanical Microscopical Slides. 



Mr. A. Pexistox, of 5, Montpelier Terrace, Leeds, has 

 sent me a catalogue of botanical slides which contains 

 a novel feature in th.'t it not only gives the principal 

 features of the slides referred to, but in many cases 

 adds outline descriptive illustrations. Many of the 

 slides are also quite out of the ordinary run, amongst 

 which I observe a slide of oedogonium, showing 

 oogonia and so-called " dwarf males," early stages in 



the development of antheridia, developing pollen-tubes, 

 etc. The prices are very moderate and the whole list 

 shows evidence of having been the work of a botanist 

 and not a mere mounter. 



Answers to Correspondents. 



O. H. Sdi-geut, York, IT. Australia. — I am afraid that the 

 difficulty to which you refer is, as you suggest, inherent in deep 

 eyepieces when used with ordinary achromatics. Few of such 

 objections will satisfactorily bear eyepiecing above 10 times, 

 and even then the loss of light and depreciation ofthe image is 

 noticeable. If your eyepiece is capped, it is just possible that 

 this is not correctly adjusted. Possibly also you are using a 

 larger cone of illumination than your objective will stand. 

 Few objectives will bear a cone equal to their own aperture 

 and a two-thirds or three-quarter cone is generally ample. 

 Vou can judge of the size by removing the eyepiece and look- 

 ing down the tube. All camerae lucidae require considerable 

 practice before satisfactory results are obtained. You would 

 probably find the Swift-Ives type as easy to use as the .^bbe, 

 but it too requires practice. The great secret is the careful 

 adjustment ofthe light, and I think the best way is to have two 

 lamps, one to illuminate the object in the microscope and one 

 to illuminate the paper on which you are drawing. The flames 

 of each lamp can then be carefully adjusted, until the bright- 

 ness of the microscope field does not overpower the illumina- 

 tion of the paper, or vice versa. You will find very different 

 adjustments are required for any change of magnification, I 

 Ihuik you will find an ordinary twelfth immersion objective of 

 N.A, 1-25 or so perfectly satisfactory, and there is very litile 

 to choose between those made by the leading makers. The 

 cost will be £5. But all your objectives must be used with the 

 tube-length for which they are corrected. As vour eye be- 

 comes more trained yon will perceive this yourself, especially 

 for such critical work as cytology. The study of the pollina- 

 tion and fertilization of \V. Australian plants ought to prove an 

 almost inexhaustible field for work of all kinds if you work at 

 it steadily and earnestly, 



A. I. Robinson, Portsmouth. — I have had no experience my- 

 self in mounting diatoms in either carbon bisulphide or 

 quinidine, and the nearest reference I can give you is a 

 method by Mr, A, W, Griffin on mounting in solution of phos- 

 phorus in carbon bisulphide, which has a very high refractive 

 index but needs great care. As a precaution against getting 

 the phosphorus under the finger nails it is best to well oil or 

 vaseline the hands. Procure some clean, semi-transparent 

 phosphorus, cut off some pieces under water with a pen- 

 knife, place them for a few seconds on blotting paper to free 

 them from any least trace of water, and dissolve in carbon 

 bisulphide, say, one drachm of phosphorus in two drachms of 

 the solvent. When quite dissolved, slightly damp a piece of 

 filter-paper with bisulphide, and carefully filter into a small 

 stoppered bottle through a very small glass funnel. Support 

 both funnel and filter paper in a basin of water to prevent 

 accident, and have the basin handy throughout in order to 

 place in it any article which has been touched by the phos- 

 phorus solution, in order to prevent accidental combustion. 

 Supposing the diatoms are preserved in water or spirit, place 

 a drop of the fluid on the cover-glass and slowly evaporate 

 the medium over the flame of a spirit lamp or jet of gas. 

 When the cover-glass is quite cool place on the margin of its 

 edge a mere speck of Canada balsam, the object of which is 

 to keep the cover, with its surface covered with diatoms, face 

 downwards, in the centre of the glass slip. By means of a 

 pipette take a few drops of the phosphorus solution and place 

 them on the edge of the circle, and by capillary attraction 

 they will be at once drawn under, displacing the air in their 

 progress. Having ascertained that the diatoms are completely 

 immersed in the medium, remove all superfluous particles of 

 phosphorus with a piece of blotting paper damped with 

 carbon bisulphide, and consign it also to the basin of water. 

 Ring with glucine or Kay's coaguline, put aside to dry for six 

 hours or more, ring again, and then, if preferred, ring finally 

 with shellac, varnish or asphalt. 



[Communications and enquiries on Microscopical matters are invited 

 and sliould be addressed to F. Skillington Scxla, "Jersey," 

 St. Barnabas Road, Cambridge.'] 



