November, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



281 



The " Ashe-Finlayson " Comparascope. 



This instrument is the joint invention ot Messrs. 

 Ashe and Finlayson, and its object is to enable an ob- 

 server to make an exact comparison of two different 

 objects by showing them simultaneously in the same 

 microscope field. The principle is quite simple. What 

 is practically a second microscope is placed horizontally 

 and at right angles to the optic axis of the microscope 

 proper. This second microscope in its simplest form 

 is a horizontal bar, carrying at one end an objective, and 

 at the other end a mirror with universal movements, 

 whilst between the two is a clip serving as a stage and 

 moving by rack and pinion, the position of the objec- 

 tive itself being necessarily fixed. Between the nose- 

 piece and objective of the microscope itself is screwed 

 a tube about an inch long, with a hole at one side to 

 which the auxiliary horizontal apparatus is attached. 

 Inside this aperture is fixed a reflector of tinted glass, 

 worked to a perfect plane on its upper surface, and 

 placed at an angle of 45° to the microscope axis so as 

 to reflect the secondary image upwards to the eye- 

 piece. But in order to allow free passage of the light 

 from the primary objective this reflector does not pro- 

 ject more than half-way into the tube. Further, to 

 prevent the overlapping and confusion of images, each 

 set of rays is confined to its own side of the field of 

 view by a removable division plate, which extends from 

 the short tube containing the reflector to within an inch 

 or so of the ocular, the tube being thus divided into 

 semi-cylindrical sections, each of which transmits rays 

 from a different object, and the image of which occu- 

 pies different segments of the field of view. The in- 

 ventors have also used a prism instead of the reflector, 

 but have found the latter to be equally efficacious and 

 more simple. The apparatus is made by Messrs. R. 

 and J. Beck, Ltd., of Cornhill. It is quite simple to 

 use. 



Watson's BoLctil Microscope. 



Last month I called attention to a new microscope 

 by Messrs. W. Watson and Sons, which, whilst con- 

 forming outwardly and in appearance to the Continental 

 model, retained many of the principles which dis- 

 tinguish the English stand, more especially the lesser 

 fine adjustment. An elaborated form of this micro- 

 scope, which is to be known as the " Bactil," possesses 



one or two additional features that are worth a further 

 note. A mechanical stage can be made either detach- 

 able or as an integral part of the stand. In the former 

 case it is ver\' liable to deteriorate in its working parts 

 and to fail in rigidity, and in the latter case it suffers 

 when rough work is being done. In the " Bactil " 



microscope the horizontal movement works above the 

 stage and is attached to it by thumb-screws so as to 

 be removable, whilst the vertical movement is fixed 

 below the stage, out of harm's way, and is non-re- 

 movable. Incidentally the long range of movement of 

 the detachable form of mechanical stage is thus 

 attained. The other noticeable feature in this micro- 

 scope is the fitting, when required, of a coned con- 

 denser, carrying the iris diaphragm, which can be 

 readily turned down out of the optic axis if necessary. 

 The arrangement is very similar to that already seen on 

 some Continental stands, notably one of Zeiss', and 

 was first introduced, I believe, on an English stand by 

 Messrs. Ross. The subsidiary iris diaphragm im- 

 mediately beneath the stage always seems to me, how- 

 ever, somewhat unnecessary. 



Notes and Queries. 



Major E. F. Bcccher, Chcltaiham. — I shall be very glad to 

 give you any assistance in my power, but I am afraid I cannot 

 advise you unless I know more definitely the nature of the 

 investigations you wish to make. Histological methods vary 

 greatly according to the end in view, and a fixing or staining 

 agent that would serve one purpose might be quite useless for 

 another. If you will let me know exactly what investigations 

 you wish to carry out, I will iry and make some suggestions as 

 to how to set about them. 



H. Cliff, Stafford. — The best book dealing with vegetable 

 parasites is Tubeuf s '■ Diseases of Plants," translated by 

 W. G. Smith, and published by Longmans in 1S97. A very 

 elementary and simple little book is M.C. Cooke's " Rust, Smut, 

 Mildew, and Mould ; an Introduction to the Study of Micro- 

 scopic Fungi," published by \V. H. Allen and Co., but I am 

 not sure whether this is not now out of print. Second-hand 

 copies are quite easily met with, however, and would not cost 

 more than a few shillings. With regard to insect parasites on 

 plants, you might get Miss Ormerod's " Manual of Injurious 

 Insects." I am afraid none of these will give you much infor- 

 mation as to preparing objects for the microscope, but I shall 

 be glad to help you so far as I am able if you get into any 

 difficulty. 



A. H. Ghiistcr, Darlington. — As far as my inquiries go, it 

 seems very improbable that MeniUus Uicrynians forms resting- 

 spores of any kind, and indeed it would be contrary to any- 

 thing that has hitherto been observed with regard to the whole 

 group to which this fungus belongs. The specimens you sent 

 were not sufficient to pronounce an opinion ; but it seems 

 doubtful whether the fungus you have been examining is really 

 Muriiliiis. Under any circumstances the conditions under 

 which you have made the cultivation have vitiated any trust- 

 worthy results, as your observing •' swarm-spores " (which 

 might be mycomycetes or infusoria !) shows the culture to 

 be contaminated. I think, therefore, it may be assumed that 

 the spores which you have observed are really those of some 

 other fungus. I am glad you succeeded in resolving ampki- 

 pleura pdlucida with oblique illumination, but if mounted in a 

 medium of sufficiently high refractive index it ought to be 

 resolvable with axial illumination with an immersion lens of 

 i'25 N.A. The condenser should be carefully centred, the 

 edge of the lamp flame focussed rigidly upon the diatom, and 

 then the condenser should be racked up the merest trifle 

 within its focus. 



A. RoK'land, Newport. — There is an excellent book on Chiro- 

 nonius, by Miall and Hammond, published by the Clarendon 

 Press, in 1900, which is a model of what such a book should be 

 and gives explanations as to methods. With regard to the 

 general structure of Bees you had better refer to Dr. Sharp's 

 volume on •' Insects," part ii., in the Cambridge Natural 

 History. I am glad you found the note en glycerine mounting 

 helpful. I do not think caoutchouc cement would be satis- 

 factory for glycerine mounts. 



[C^ommunicatwns and Enquiries on Microscopiail ni.ilters should be 

 addressed to F. Shillington Scales, "Jersey," St. Barnabas Roal, 

 Cambridge.] 



