THE SLIT-LAMP 



41 



axis, O ; L is for locking the lamp-casing in position once it has 

 been pushed or pulled, and twisted, into the correct position so 

 that the image of the lamp filament S is both correctly focused 

 and vertically set ; T is for locking the body of the slit-lamp in its 

 encircling collar ; A is for locking the diaphragm-plate after it 

 has been set with the slit disposed in any desired axis, though this 

 is nearly always used \'ertically set ; p represents the plane of 

 the slit, whose width can be increased or diminished by the screw W 

 (it is better, by loosening first the screw T, to rotate the whole 



/> 



FL. 





T 



Fig. 8. — Slit-Lamp. 



body of the apparatus round so that A lies underneath and W is 

 on top where it is more accessible for manipulation) ; d is an 

 accessory diaphragm-plate mounted on a spindle and having 

 round or square holes of different diameter, any one of which may 

 be rotated into the optical axis w^hen a small round or square 

 beam is desired instead of a ribbon-like beam from a slit, the jaws 

 of the slit then being screwed w^de apart so as to leave free access 

 to the round or square aperture. B is a long arm supporting the 

 focusing lens FL, which can be racked horizontally to and fro by 

 means of the screw X ; Y (Fig. 9) is the Arruga fitting, enabhng 

 the lens FL to be moved up and down along a vertical direction. 

 The lens FL is set in front of a rectangular diaphragm-plate having 



