ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



715 



to the combined efforts of V. Legros and M. Stiassnie, is intended to 

 bring into the regular practice of the workshop and of centres of 

 microscopical instruction, the results which formed the subject of a 

 previous communication* byM. V. Legros. The base C (fig. 118) is a 

 divided circle from whose centre arises a vertical column J), terminated 

 by a horizontal sleeve T. In this sleeve there glides, governed by a 

 rack-and-pinion p, a rod on which move also under the action of 

 pinions p', p", two other sleeves bearing the optical parts. These sleeves 

 can ride one over the other, their displacements being measured by 

 verniers. The sleeve manipulated by p' has also a slow movement 

 governed by a screw with divided head V. The part A represents the 

 body of an ordinary Microscope with its stage P : a slight displacement 

 can be given by the revolver for purposes of parallax. The stage and 

 substage are fitted with centring and rotating movements. Micrometers 

 are fitted to both faces of P, and the orifice in the snbstage is provided 

 with interlocking screw-jaws for receiving optical systems. Details are 

 given of the methods for measuring (1) the focal length of an objective 

 or ocular ; (2) the angle of aperture ; (3) distortion. 



Fig. 119. 



Desains' Apparatus.! — This instrument (fig. L19) is intended for 

 measuring wave-lengths by Newton's rings. 



* Comptes Rendus, cxxxvii., Jan. 29, 1900. 



t Cat. Soc. Genevoise pour la Construction d'lnstrnmetits de Physique et de 

 Mecanique, 1900, p. 111. 



