The Oblique Illuminator 



269 



because it has, as yet, only been applied to instruments made on the 

 Jackson model, and it has never been my good fortune to find 

 one constructed on that plan, which was suitable for my work. 

 The reason of this is twofold ; first, because, when I use the 

 objective alone (without eye-piece or amplifier) to project the 

 image upon the screen, I frequently desire to remove the microscope 

 body, leaving the objective in place, which cannot be done with 

 stands constructed on the Jackson model ; and second, because I 

 have never yet met with a stand of that model in which, when the 

 image was projected to a distance of nine or ten feet with a high 

 power, the fine adjustment did not introduce an embarrassing 

 degree of lateral displacement. I have, therefore, for some time, 

 used a little piece of apparatus which enables me, on my large 

 Powell and Lealand stand, or any similarly constructed instru- 

 ment, to obtain with certainty any 

 desired obliquity of illumination. It 

 has been suggested to me that others, 

 possessed of instruments of like pat- 

 tern, would find it useful, and hence 

 this brief memorandum. 



Fig. 9 is a perspective view of 

 the apparatus (slightly reduced 

 in size). It consists of a trans- 

 verse bar of brass (i), at one 

 end of which, attached by a 

 hinge (2), is a square brass plate (3), 

 which can be inclined at any desired 

 angle. This plate is transfixed centrally 

 by a brass tube half an inch long, in 

 which a second tube (4) an inch and a 



