ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



233 



ing all decentring of the microscopic stage in relation to the optical axis 

 of the Microscope. The rotation of the nicol is obtained by means of a 

 pillar, parallel to the Microscope, and bearing two pinions engaging in 

 two small stages supporting the polarisers and analysers. The polariser 

 is fitted with a quick-movement screw tor raising or lowering. The 

 object-stage can be rotated, as desired, independently of the nicol ; it 

 carries a pivoting condenser.* 



Mechanical Stages.f — Fig. 38 represents a mechanical stage 

 designed for use with the above mineralogical and petrographical 



Fig 38. 



Microscopes. The apparatus is constructed with crossed carriers for 

 centring ; it has a coarse-adjustment by raekwork, and a fine-adjustment 

 byJa micrometer screw with divided head. 



Fig. 39. 



Fig. 39 shows Fedorow's stage.! It is made in two forms : a small 

 model, with two movements of rotation ; and a large model, with four 



* There is a great resemblance to Swift's patent, which has, however, perhaps 

 run out. — Ed. 



f Catalogue of the Societe genevoise pour la construction d'instruments de 

 physique et de mecanique, 1907, No. 2421 (fig. 2121a). 



% Op. cit., Catalogue No. 2192. 



April 15th, 1908 R 



