540 



Proceedings of the Royal Thy deal Soeiety. 



the model of that used first in Germany. The special 

 points to be noted in this are, (1.) the microscope (with 



Fig. 19. 



(«) Laini3 ; (6) microscope ; (c) velvet tube ; {d) focussing screen ; 

 (e) dark slide; (/) bull's eye condenser, 



condenser attached) and lamp are placed on a board re- 

 volving on a pivot on the long base board, so that the 

 object may be fixed and focussed before the microscope tube 

 is inserted into the front of the camera. (2.) The focussing 

 on the screen is rendered much easier by an arrangement 

 suggested first by Mr G. Brook and then by Dr Edington, 

 whereby the milled head of the line adjustment screw is 

 worked by means of a cord running from the end of the 

 focussing rod over the groove of the milled head, sufficient 

 friction being obtained by means of a plummet ball, 



