ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



249 



dent. By means of S' the tube (with the objective) is carefully moved 

 over the dent until the first cross-thread reaches a similar tangential 

 position on the opposite sidp. The reading of the vernier gives the 

 diameter of the circular dent. A shade r and lens / are provided to 

 facilitate reading the vernier. In the case of large objects the whole 

 instrument is placed on the specimen so that the aperture X is over the 

 dent. 



(2) Eye-pieces and Objectives. 



Reichert's Objectives with Bourguet's Spring Safety Action.* — 

 C. Reichert has fitted this protective action to all his achromatic 



Fig. 44. 



Fig. 45. 



objectives numbered 6 and upwards. The arrangement is shown in 

 figs. 44 and 45. Under ordinary circumstances the elasticity of the 

 spring keeps the combination in proper adjustment, but if there should 

 be contact with the object, the lens-holder is pushed within its sheath. 



H. — Construction of Aplanatic Combinations of Lenses with or without Achroma- 

 tism. IV. English Mechanic, lxxx. (1905) pp. 595-6. 



(3) Illuminating- and other Apparatus. 



Reichert's Swing-out Condenser and Iris Diaphragm.f — The 

 complete arrangement is shown in fig. 46. It will be seen that the con- 



Fig. 46. Fig. 47. 



denser can be swung out of the iris by the action of the hinge Ch, which 

 is operated by twisting the bifid lever. Fig. 47 shows the condenser in 

 more detail. 



* C. Eeichert (Vienna), Catalogue No. 25 (Mikroskopie, 1904) p. 5. 

 April 19th, 1905 s 



