SeptembeRj 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



549 



the microscope. A little juggling- -with the two lamp- 

 wicks will often work wonders. Another suggestion 

 that can be made is to blacken the end of the pencil or 

 to tip it with gold-leaf. Finally, distortion of the draw- 

 ing must be guarded against, especially with forms like 

 the Abbe apparatus, which can be used with the micro- 

 scope slightly inclined, and, if necessary, an inclined 

 drawing-board must be used. 



New Portable Dissecting Microscope. 



Messrs. R. and J. Beck have brought out a new dis- 

 secting microscope which is not only portable, but when 

 folded up contains all the necessary apparatus packed 

 into the thickness of the wood, so that there are no pro- 

 jections or loose pieces. The illustrations make the 

 principle clear, the two side flaps, which spread out as 

 rests for the hands, being hinged and folding back when 



not in use. The wooden taijle has a circular aperture 

 into which drops a white porcelain saucer, which is 

 concave on one side and flat on the other, and can be 

 used either way up, or a piece of transparent glass may 

 be used in place of the saucer, in which case light may 

 be thrown from below by means of a folding flap which 

 carries a white reflector. The lens carrier consists of a 



tube which fits into a socket in the table, and carries a 

 double arm by means of which the whole aperture can 

 be examined. The vertical adjustments are made by 

 means of a lever. The whole apparatus, with two 

 single lenses, saucer, glass plate, focussing adjustment, 

 and two needles packs into a space 9 ins. by 3j ins. by 

 i^ in., and costs 35s. 



A New Application of the Abbe Condenser 



The " Journal " of the Royal Microscopical .Society 

 summarises some observations of a Continental worker 

 which are based on the fact that the .\bbe condenser 

 presents a real, reversed image of the source of illumina- 

 tion. If an object, such as a micrometer scale, be 

 suitably interposed, an image of this will be similarlv 

 formed on the stage, and may be applied to measuring 

 an object there. In this way, by the help of a propor- 

 tionately stronger objective, a series of magnifications 

 can be obtained which are very convenient for drawing, 

 and for the preparation of various objects. The size of 

 the image formed above the front lens (viewed from 

 above) of the condenser depends on the distance of the 

 object from the under-lens; the image is smaller as the 

 distance is increased. Thus it will be seen that the 

 series of magnified images thrown on to the stage will 

 vary from zero to a maximum. This image can be 

 combined with various powers of oljjective, eye-piece, 

 and tube-length, and thus tiie series of attainable effects 



is practically infinite, although only observations in the 

 middle of the field ■ft'ill be free from sensible distortion. 

 Instead of the condenser, weak achromatic objectives 

 might be used. A difficulty would, no doubt, lie in the 

 construction of a suitable adjustable stag^e for the ob- 

 ject; the author, however, sees his way to a proper de- 

 sign. He summarises the advantages of this proposal 

 aa: — (i) The facility for orientating objects which can 

 be afterwards examined in the usual way. (2) The 

 formation of graduated magnifications by which an 

 operator who wishes to draw from a weak magnifica- 

 tion can easily select the most suitable power. {3) The 

 property possessed by the Abbe (thus used) in combina- 

 tion with an objective of forming an erect i nage. (4) 

 If a plane mirror be used, and the object inserted be- 

 tween the light-source and the mirror, an erect micro- 

 scope becomes virtually a horizontal one, and may thus 

 be used, for example, as an acjuarium microscope. (5) 

 As the magnification may be zero, the arrangement may 

 be applied to the drawing of objects in their natural size.. 



Temporary Mounting of Objects. 



It often happens that objects are required to be 

 mounted temporarily only, and without the more 

 elaborate processes which are necessary for permanent 

 mounting. Such objects can be mounted in a drop of 

 the preservative, or in water, or in alcohol and formalin 

 according to the medium in which the object may be, 

 whilst normal salt solution (common salt .0 per cent, in 

 water) is often of great use. Living objects are best 

 mounted in their natural medium, as any change may 

 alter their appearance, or, at least, inhibit their move- 

 ments. In all these cases, however, rapid evaporation 

 of the liquid takes place, and some means of sealing 

 the cover-glass is necessary. For this purpose vaseline, 

 cas'tor-6il, or gfycerine jelly have all proved useful, and 

 a method that is of service in many cases, especially 

 where what are known as " hanging drops " are being 

 dealt with, is to use a paraffin match, or a toy w'ax 

 candle by blowing out the light, and whilst the paraffin 

 is still liquid running it like a brush along the edge of 

 the cover-glass. In all cases it is necessary to have 

 sufficient of the mounting medium to prevent soft ob- 

 jects from being crushed, and, on the other hand, to 

 avoid any excess which would cause the cover-glass to 

 float, or to spread beyond the edges. Such surplus can 

 readily be removed with blotting paper, care being 

 taken lest the capillary attraction draws too much liquid 

 from beneath the cover-glass. It is well to lower the 

 cover-glass edgewise gently upon the object in order 

 to avoid bubbles. 



John Wheldon and Co.'s Catalogue. 



Messrs. John Wheldon and Co., of 38, Great Queen 

 Street, W.C, have just issued a catalogue of books 

 and papers on Microscopical Science in all its branches, 

 which contains many interesting items, including 

 numerous books on the microscope itself. 



Microscopical Material. 



Mr. J. .Sciflthorpe, of Bath, has kindly sent me for 

 distribution a considerable quantitv of sea-sand from an 

 unknown locality, which well repays looking over under 

 the microscope, and from w'hich interesting marine 

 debris can be picked out. I shall be glad to send an 

 ounce or two of this to ;inyone who applies for it. Ap- 

 plications must be accompanied by a stamped and ad- 

 dressed envelope, a wooden or tin box, and the coupon 

 to be found in the advertisement pages of this issue. 

 [Commuiiiciitions and Enquiries o» Microscopical matters should be 



addressed to F. Shillinglon Scales, "Jersey," St. Barnabas Road, 



Cambriilge.] 



