554 SUMMARY OF CURRENT RESEARCHES RELATING TO 



A is a brass plate, 3 inches by 1^ inch, in the centre of which is a 

 round hole. At one end is a bent spring B, of thin brass, to which 

 is hinged a second brass plate C, also with a central round hole, 

 and bevelled on the upper surface for high powers. This second plate 

 will, when turned down, overlie the plate A, and the two apertures 

 will correspond. At the other end of the plate A, a button D is 

 mounted so as to turn freely, and to rock on a short stud pin d. The 

 outer extremity of this button is bored and tapped to receive a small 

 thumb screw e. A similar thumb screw / is also fitted to the plate C, 

 near its hinge joint. 



A thin cover-glass is cemented to the upper side of the plate A, 

 so as to cover the central hole, and the under side of the plate C is 

 similarly provided. 



The mode of using this compressor is as follows : — The plate C 

 is first turned down into place, and the distance that it is desired the 

 glasses should be apart roughly adjusted by means of the screw/. 

 The plate C may then be turned back, and the object placed on 

 the lower glass ; the covering-plate is then again turned down and 

 secured by turning the button D over it. By means of the two 

 screws d and /, the pressure can now be regulated with the greatest 

 nicety without any risk of damaging or losing the object under 

 examination. The arrangement admits of the glasses being easily 

 cleaned and readily replaced by new ones when broken. 



Bulloch's Diatom Stage.* — Mr. W. H. Bulloch has made a supple- 

 mentary stage for use in arranging diatoms. It fits into the substage 

 ring, and a stem projects up through the hole in the main stage. 

 Upon the stem there is an arrangement like a double nose-piece, 

 which carries two glass slips. One of the slips is intended for the 

 material from which the diatoms are to be selected ; the other for 

 the prepared slide upon which they are to be mounted. The two 

 slips can be moved about independently upon their supports. The 

 hair or bristle is mounted on the mechanical stage. The slide carrying 

 the material is first focussed, the diatom picked up, and the supple- 

 mentary stage turned until the clean slide is in focus, when the diatom 

 is placed in position. 



Substage Fine-adjustment. — At the suggestion of Mr. E. M. 

 Nelson, Messrs. Powell and Lealand have recently applied a fine- 

 adjustment to their substage specially for use with their achromatic 

 condenser. Fig. 99 shows (half-size) the under side of the substage 

 with the new fine-adjustment in which A is a milled head controlling 

 a screw-spindle terminating in a steel cone B. On rotating A, B turns 

 and with a very slow motion forces up (or releases, as the case may 

 be) a pin C inserted in the base-plate E of the substage. This 

 motion of C carries with it the condenser. At right angles to, and 

 forming part of E, at the back, an inner sliding plate works against a 

 spring at the upper end between bearings F at each side, which are 

 fixed upon the usual racked slide D of the substage ; this inner 



* Amer. Mon. Micr. Journ., iii. (1882) p. 97. 



