ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



365 



no doubt, lie in the construction of a suitable adjustable stage for the 

 object ; the author, however, sees his way to a proper design. He sum- 

 marises the advantages of this proposal as :— 



1. The facility for orientating objects which can be afterwards 

 examined in the usual way. 



2. The formation of graduated magnifications by which an operator 

 who wishes to draw from a weak magnification can easily select the 

 most suitable power. 



3. The property possessed by the Abbe (thus used) in combination 

 with an objective of forming an erect image. 



4. If a plane mirror be used, and the object inserted between the 

 light-source and the mirror, an erect Microscope becomes virtually a 

 horizontal one, and may thus be used, for example, as an aquarium 

 microscope. 



5. As the magnification may be zero, the arrangement may be 

 applied to the drawing of objects in their natural size. 



Post-Objective Stop.* — At the March Meeting, J. W. Gordon 

 exhibited a new form of post-objective stop for the Microscope, an 

 illustration of which is now given (fig. 46), together with a description 

 of the various parts. 



Fig. 46. 



A. Cell carrying the mercury globule which forms the stop. 



B. Pivot on which the cell-carrying arm swings. 



C. Excentric for swinging the arm, and so giving a transverse travers- 



ing adjustment to the stop. 



D. Propelling screw for giving a longitudinal traversing motion to 



the pivot B and so to the stop. 



E. Supporting screw for adjusting the height of the swinging arm 



and of the stop carried by it. 



F. Mounting ring, provided with a set screw, for clamping the fitting 



to the draw-tube of the Microscope. 



Use of the Cooper-Hewitt Lamp as a Source of Monochromatic 

 Light.f — C. Fabry and EL Buisson warmly recommend this lamp, which 

 is on the principle of an electric arc in mercury vapour. Its spectrum 

 resembles that of the older mercury vapour lamps. The light is fixed, 



* See this Journal, 1906, pp. 157-60. 

 f Comptes Rendus, cxlii. pp. 784-5. 



