938 



The light intensity is generally reduced with a sliding contact 

 variable resistance. 



A condensor projects the image of the filament on a narrow slit. 

 A lens placed on the slit projects the condensor aperture on the 



ophthalmoscope lens, the light hreing deflected 90 degrees by a small 

 totally retlecting prism placed beneath the slit, so as to permit of 

 placing the illuminating tube at a right angle to the axis of the 

 viewing tube, containing the ophthalmoscope lens. The real image 

 of the retina, formed by the ophthalmoscopelens can be examined 

 through an aperture beneath the prism. We inspect that image with 

 a kind of short microscope, the objective of which has a focal 

 distance of 55 millimeters, the eye piece being one of the Huygenian 

 type as used in the ordinary microscope. The magnification is altered 

 on the use of different eyepieces. 



In order to eliminate the images reflected by the ophthalmoscope 

 lens, the following arrangement is used. A small achromatic double 



