ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



801 



apparatus gears dowu 1 : 4, but by varying the relative diameters of 

 the plunger and the ram the ratio could ba reduced almost to any 

 extent— e g. a plunger of 1/12 in. and a ram 1/2 in. would gear down 



Fig. 131. 



Fig. 132. 



4: 



y 



Fig. 133. 



in the ratio of 1 : 36, so that one revolution of a 50-thread screw 

 would only make a movement of 1/1800 of an inch in the 

 objective." 



Griffith's Nose-piece. — Mr. E. H, Griffith suggests yet another 

 form of nose-piece as shown in fig. 133. The adapter has a short pin 

 fitted on the inner surface of the cylinder, while 

 the ring for the objective has a bayonet slot. 

 The ring is as deep as the Society-screw to the 

 objective, allowing it to be put into the box witli 

 the latter. This device was employed by Cheva- 

 lier many years ago. 



Kellner Eye-piece with additional Lens as 

 a Condenser. — At the closing meeting of the 

 last Session, after Dr. Wallich had pointed out 

 the advantages of his new form of condenser, 

 Dr. E. L. Maddox explained the plan he had used 

 for some time, especially when photographing 

 minute objects, such as bacteria. Instead of the 

 usual pin-hole in the cap of a Kellner eye- 

 piece, he substituted a movable diaphragm, with 

 a small deep lens of 1/12 in. radius and of 

 some thickness. The diaphragm, with lens duly centered, slides by 

 friction in the cap of the eye-piece, and is pushed up close to the 

 ordinary opening ; the cap is then closed down upon the eye-lens to 

 the best position for the purpose required. Single lenses of other 

 radii can also be tried. The whole is used as a substage condenser, 

 and with or without the usual diaphragm wheel. 



