Feb., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



43 



Method I. — With the image of a stop. Method II. — 

 With the stop and the vertical illuminator. 



The accessories necessary for Method I. are (i) 

 source of light ; (2) carrier for stop ; (3) condenser ; 

 (4) vertical illuminator. The condenser is first set 

 between the light and the vertical illuminator, so that 

 it forms an aerial image of the source of light at a 

 distance from the vertical illuminator equal to that 

 from the vertical illuminator to the top of the eye- 

 piece. The carrier for the stop is then placed between 

 the light and the condenser in such a position that its 

 aerial image is exactly adjusted and falls sharply in 

 focus at the back lens of the objective. This will give 

 an effect precisely the same as placing a stop or 

 diaphragm over the vertical illuminator itself, while the 

 upward path of the rays from the object to the eye is 

 unimpeded. 



The accessories necessary for Method II. are 

 (i) source of light; (2) bull's-eye condenser; (3) 

 vertical illuminator with stop or diaphragm fitted to its 

 side. For this method, the lamp and bull's-eye are 

 adjusted as in Method I., care being taken that proper 

 distances are kept, when the same effect will be pro- 

 duced as with a stop or diaphragm placed immediately 

 over the vertical illuminator. 



New Vertical Illuminator and New 

 Monochromatic Trough. 



Messrs. R. and J. Beck, Ltd., have brought out a 

 new vertical illuminator of the prism type fitted with an 

 iris diaphragm beneath the prism for cutting off out- 

 side light, and a plate of stops so arranged that the 

 position of the beam of light impinging on the prism 

 can be varied until parallel light of the right angle is 

 obtained. The vertical illuminator is largely used now 

 to illuminate the surface of metals when making 

 metallurgical examinations with the microscope. The 

 principle is that a beam of light sent at right angles to 

 the optic axis of the microscope is reflected by a prism 



or piece of cover-glass down upon the object so that 

 each objective acts as its own condenser. It is probably 

 the only means of illuminating objects mounted dry 

 when they are examined with immersion lenses, though 

 in this case it is necessary that the object should be in 

 actual contact with the cover-glass. 



The trough is noticeable for its compactness and 

 easy adjustability. It can be brought as low as one 

 inch from the table or raised to a height of nine inches. 

 The fluid used in the cell depends upon the required 

 colour of the light. 



Notes and Queries. 



Examination of Water. 



Johti Ciin-iiigtoit, East London, S.A. — I do not thinU you 

 •-vould find anything in town-water unless it was very bad. 

 Under any circumstances a Botterill's trough would not do, 

 as the thickness of the glass and the depth of the cell would 

 prevent your using a high enough power. I would suggest 

 your getting a sample of water from a stagnant pond or old 

 tub, taking up a few drops with a glass tube, and by examining 

 it in an ordinary excavated cell, covered with a thin cover- 

 glass, you will find enough to interest you there. The weird 

 animal life exhibited sometimes in a drop of water at lectures 

 has, I am afraid, been specially selected to astonish the 

 audience. 



Deane's Medium. 



Mr. T. H. Russell, of Birmingham, would be glad to know 

 if any reader of these columns has had any experience of 

 Deane's medium for mounting vegetable specimens for the 

 microscope. He says he has been in the habit of mounting 

 his mosses in glycerine jelly, but, like most people who use it, 

 has found it somewhat treacherous. He has found Deane's 

 medium more reliable in some ways, but it has a tendency to 

 shrixel up certain specimens — t'-.i;., some large-celled mosses — 

 directly they are immersed in it. He tried boiling them first 

 in a little dilute glycerine and water, also adding a little water 

 to the medium, but without improvement. He would be glad 

 of suggestions as to the cause of this, or a formula for making 

 the medium other than that given in Davies' book on " Mount- 

 ing Microscopic Objects." I do not think I have ever used 

 this medium myself. Can any reader make any suggestions ? 

 Naming Specimens. 



H. II'. ]'., BiriniiigJiam. — I am anxious to help my readers 

 as much as possible, but I do not think you quite realise how 

 much work is involved in naming specimens. Microscopy 

 covers so wide a field that it is impossible for one man to 

 have the minute specialized knowledge necessary for identify- 

 ing specimens in the whole field of Nature, and I have there- 

 fore to get my friends in Cambridge and elsewhere to assist 

 me in such matters. For instance, I would rather not name 

 specimens of either fungi or mosses, and I hesitate to hand 

 them over to specialists unless I am quite sure that they 

 are more or less uncommon species which have an unusual 

 interest to some correspondent who is working specially on 

 them. If this bo so in your case I will do what I can for you, 

 but I trust you will forgive this public reference, because I 

 receive so many requests to name specimens that I have 

 thought some little explanation may be of service. On purely 

 microscopical matters I am glad always to do what I can, 

 however elementary the questions. 



Observation of Flagellar and Cilia. 



/. If. Broicii, Inveykcithing. — The J-inch objective you 

 mention is an excellent one, but flagellse and cilia are generally 

 most difficult to see, especially if the animal is alive. Your 

 best plan will be to add a little cocaine to the water and watch 

 till the movement begins to slow down, when you may be 

 more successful. I do not think a more costly lens would be 

 of any greater service to you, but you are not giving 

 either yourself or your objective a fair chance if you have not 

 got a sub-stage condenser. The improvements in modern 

 high-power objectives are almost nullified without a con- 

 denser. Could you not extemporise a ring that would enable 

 you to use a 2-inch or i-inch objective as a condenser ? You 

 will find, however, that the absence of an iris diaphragm to 

 adjust the light is yet another drawback, as cilia will not bear 

 a large cone, being so lacking in contrast. You cannot get 

 good dark-ground illumination with lenses of higher aperture 

 than about •& N.A.,in fact you will probably fiud any objective 

 higher than a half-inch does not give good annular illumina- 

 tion. The spot must be proportioned to the aperture of the 

 objective, the larger the angle (that is, generally, the higher 

 the power) the bigger must be the spot. 



{Communications and enquiries on Microscopical matters are invited, 

 and should be addressed to F. Shillington Scal:s, "Jersey," St, 

 Barnabas Road, Cambridge.] 



