94 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



M. Houdaille that it might be of advantage to make the objective itself 

 act as a filter. After consultation with the firm of Parra-Mantois, a 

 uranium-glass, 10 mm. thick, absorbing 10 p.c. of the visible rays, and 

 50 p.c. of those incident on the photographic plate, was selected. From 

 this glass a compound objective was cut from a design calculated by the 

 author. The results w 7 ere compared with those obtained by a colourless 

 objective. With equal exposures the negatives obtained by the uranium- 

 glass were clearer and could be longer developed. The tones corre- 

 sponding to the yellow rays were deepened, and those corresponding to 

 the blue weakened, while the plates were uniformly bright to the very 

 circumference. 



(3) Illuminating- and other Apparatus. 



Watson and Sons' Vertical Illuminator.* — This apparatus is 

 made in two forms : (1) with a prism ; (2) with a disk of very thin 

 glass. In the prism form (fig. 10) light concentrated by a bullseye is 

 passed through a small aperture in the side of the illuminator. It is 

 then reflected through the objective to the specimen, the objective acting 



Fig. 10. 



Fig. 11. 



Fig. 12. 



as its own condenser. In the glass disk pattern (fig. 11) the light is 

 conducted in the same way as in the prism form, but the reflection 

 is effected by means of a very thin disk of glass set at an angle of 45° to 

 the optic axis. 



Another variety of the disk pattern is seen in fig. 12. It is of 

 square form with an iris diaphragm mounted on a plate sliding in a 

 groove, allowing the light to fall obliquely or directly upon the reflecting 

 glass as desired. This vertical illuminator can only be employed with 

 Microscopes having a body of large diameter. If necessary, the iris 

 diaphragm may be mounted on an excentric, so that vertical adjustment 

 also may be obtained. 



Watson and Sons' " Grip " Stage-spring, f — Four advantages are 

 claimed for this pattern (figs. 13, 14) : (1) free rotation of the spring ; 

 (2) firmly fixed butt ; (3) removal of spring and butt with perfect ease ; 

 (4) non-liability of objectives to catch the spring, which lies quite flat 



* Watson and Sons' Supplement to Catalogue No. 2, p. 17, 3 figs, 

 t Watson and Sons' Catalogue, 19th edition, 1907-8, p. 12. 



