574 SUMMA.RY OF CURRENT RESEARCHES RELATING TO 



attached to a sliding and rotating rod carried at one end of a bent 

 arm. The other end of the arm has a slot 1^ in. long fitting on 

 a clamping arrangement, which can be attached to the stage. The 

 clamp consists of a bar with a notch cut in its upper end, and with a 



short piece of tube fitting over it. The 

 Fig. 107. ^^ bar is pushed up by a spiral spring, but 



when the milled head beneath is turned, 

 it is drawn down within the tube, thus 

 shortening the length of the notch cor- 

 respondingly with the thickness of the 

 stage. The slot enables the arm to 

 be moved so that the prism may be ad- 

 justed in the optic axis with varying 

 diameters of stage. 

 The hemispherical lens might be substituted for the prism, which, 

 indeed, we think, would be found more generally useful. 



Impromptu Condenser.* — Prof. Kindfleisch suggests that tho 

 absence of a condenser may, on emergency, be supplied by a drop of 

 distilled water placed on the lower surface of the slide, where it will 

 act as a convex lens. 



Illumination by Sunlight.t — Dr. J. Edwards Smith says that " in 

 the study of very minute and delicate structures requiring the utmost 

 separating or resolving power of the objective, remarkable efi*ects are 

 to be secured by condensing sunlight on the top of the object by means 

 of the concave mirror, the object being mounted with a cover in the 

 usual way. The objective used should, of course, have wide aperture. 

 The mirror being posed slightly above the level of the stage, the sun- 

 light is thrown on the surface of the cover, and making a very acute 

 an»le therewith. Although not absolutely necessary for this purpose, 

 those stands furnished with swinging substages, allowing the mirror 

 to rise above the level of the stage, are extremely handy and con- 

 venient. By the employment of this illumination in conjunction with 

 object-glasses of wide apertures, the most difficult diatoms, such as 

 Amphipleura pellucida, FrustuUa saxonica, &c., are easily and forcibly 

 displayed." 



Monochromatic sunlight is procured most easily as follows : cut 

 with a diamond, or a point of a file, a small piece of blue glass roughly 

 to fit the cap of the eye-piece, so that when the cap is restored to its 

 place the blue glass shall be between the eye and the eye-lens of the 

 eye-piece, and the light is thus modified before it reaches the eye. 

 This is the handiest method of obtaining monochromatic light he 

 has ever tried, and the resolutions are quite as strong and effective 

 as when the cupro-ammonia cell is used in the usual manner. In 

 working with sunlight care should be taken to exclude the full 

 strength of the solar beam ; that is, if the sun be clear and bright. 



* ' Berliner Klinische Wochenschrift,' 1883, p. 183, but the above noted from 

 Bizzozero's ' Manuel de Microscopie Clinique,' French transl. by Dr. C. Fixket, 

 1883, p. 333. 



t ' How to See mth the Microscope,' 1880, pp. 186-7, 191-2. 



