494 Scientific Proceedings, Royal Dublin Society. 
point higher up in the body of the microscope. This may be 
conveniently done by utilising the aperture provided in many 
microscopes for an analyser between objective and eye-piece. 
Into this aperture a nicol, carrying at its inner extremity a totally 
reflecting prism, is pushed. The horizontal ray is received either 
from a mirror or lens, enters the nicol, and after traversing it is. 
reflected downwards, nearly in the axis of the microscope. The 
disposition is in fact essentially similar to that figured, but its. 
location higher in the microscope reduces the angle between the 
incident and reflected rays. For most purposes the use of the 
ordinary opaque illuminator, fitted with a nicol, is quite adequate. 
