ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 477 



" Your committee carefully examined the slides submitted to them, 

 but gave special attention to the slides of Amphipleura pellucida 

 movmted in a nearly white or colourless medium, whose refractive 

 index is stated to be 2 — . 



A new Bulloch Professional stand, with a 10-inch tube, was used. 

 It was fitted with a condenser made on the Abbe pattern by Mr. 

 Bulloch, the numerical aperture of which was stated by the maker to 

 be 1 • 23. The condenser was used with a homogeneous-immersion fluid 

 (cadmium chloride in glycerine). The illumination was furnished by a 

 kerosine lamp with a flat wick turned edgewise toward the mirror, and 

 the light was reflected through the condenser by the concave mirror. 



The objectives used were, first, a dry 1/6 of Bausch and Lomb, 

 said to be of 140° air angle, with a Beck No. 3 eye-piece, which gives 

 a supra-amplification of 13 '88. The angle of light from the con- 

 denser was as high as could be used by the objectives and fully 

 illuminate the object, and with these appliances the linos showed with 

 great distinctness. 



We then used a homogeneous- immersion Zeiss 1/18, 1*28 N.A., 

 with the following eye-pieces : Beck No. 1, supra-amplification 5 ; 

 Beck No. 2, supra-amplification 8 • 33 ; ToUes 1 in., supra-amplifica- 

 tion 10 ; Beck No. 3, supra-amplification 13 • 88 ; ToUes 1/2 in., 

 supra-amplification 20*83. The illumination was the same, except 

 that the angle of light was as oblique as the condenser could give. 

 "With all of these eye-pieces the beads showed very strongly. 



The slide mounted in a yellowish medium with a refractive index 

 said to be 2 • 3, did not seem to present any marked superiority over 

 the other. 



Your committee would expect these media, particularly the colour- 

 less one, to be of great value if they keep well. Their advantage in 

 the study of diatoms is obvious. We would also expect them to be 

 even more useful in histology if preparations can be transferred to 

 them without injury. They may also be of great service in the study 

 of bacteria. 



By the process of staining, now necessary in the study of these 

 structures, they are shrivelled and perhaps changed in other ways, 

 and we may hope to learn much more about them than is now known 

 if they can be studied in these media in a more natural condition." 

 (Signed by B. W. Thomas, Lester Curtis, H. A. Johnson, H. W. 

 Fuller, and H. J. Detmers.) 



Wilks's Cell. — Mr. E. Ward supplies cells for mounting without 

 pressure in Canada balsam made on a plan suggested by Mr. Wilks 

 and shown in fig. 76. 



Fig. 76. 



The cell is made of soft metal and, as will be seen from the figure, 

 has four elevations alternating with depressions, the cover-glass 



