ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 655 



the object. Thus the greatest facility is given for illuminating the 

 object at any angle, and seeing which is the most suitable. 



The prisms used are 1 inch, and give sufficient light for a y^^-inch 



Fig. 138. 



object-glass with a Eoss BB eye-piece, using of course a suitable eon- 

 denser beneath the stage. The field of a 4-inch object-glass is also 

 fully covered. It would be better to use prisms a quarter of an inch 

 larger for the highest powers. 



Griffith Club Microscope. — We gave a description and three 

 figures of this Microscope on pp. 293-6, and have since received a 

 communication from Mr. Griffith stating that sundry minor modifica- 

 tions have been made in the construction, which have improved the 

 general steadiness of the movements. 



The form of the tube carrying the stage has been changed by 

 adding rectangular longitudinal flanges on opposite sides, modifying 

 the corresponding fitting accordingly. A spiral spring has also been 

 inserted, by which the bearings are kept in closer contact. These 

 alterations give a smoother motion to the fine adjustment, and also 

 provide more substantial support for the stage. The pin sliding in 

 the spiral-grooved nut (by which the fine adjustment is effected) has 

 been split and sprung, so that it now fills the cross-section of the 

 groove, preventing lost motion and diminishing the lateral leverage 

 that formerly obtained in moving the stage. The gauge of the 

 optical-body has been enlarged to permit the use of eye-pieces of 

 larger diameter. A movable wheel of diaphragms has also been added 

 beneath the stage. 



Parkes's Child's Portable Compound Microscope. — In this instru- 

 ment (Fig. 139) the principle embodied in what are known as " demon- 

 strating" Microscopes has been applied (by Messrs. Parkes) to a very 

 cheap form of instrument sold (with a 2-inch object-glass, six objects, 

 and two glass slips with hinge for temporary mounting) for a very 

 few shillings. 



We are inclined to think that this form might advantageously be 



2x2 



