39 



Upon a Phenomenon of Monocular Vision in Connection with 

 THE Delineation of Microscopic Objects. 



By W. H. FURLONGE. 



(Read April 26th, 1872.; 



There are few departments of manipulation of greater importance 

 to the working microscopist than the means of delineating, with 

 accuracy and rapidity, the objects which, from time to time, are 

 brought under his notice. Facility in drawing from the object as 

 seen in the microscope, by the unaided eye, is a comparatively rare 

 accomplishment, and even where there exists a natural artistic 

 aptitude, it is only by long practice, and after many painful failures, 

 that such facility can be attained. Hence the value of what may 

 be termed mechanical aids in the delineation of objects, such as the 

 Camera Lucida, and other forms of reflecting prisms, the steel disc, 

 and the neutral tint reflector. 



It is not my purpose to enter into the respective merits of these 

 and other methods of microscopic drawing, but to bring under the 

 notice of the Club a phenomenon of vision connected with the 

 employment of the last-named instrument — the neutral tint re- 

 flector — which appears to me very remarkable, and deserving of 

 further investigation, not solely because of its interest in connection 

 with mental, nervous, or brain impressions, but also on account of 

 its bearing upon practical working facility in microscopic drawing. 



We are all familiar with the neutral tint reflector, and with the 

 optical principles involved in its construction. As usually made, 

 this instrument is furnished with several reflecting glasses of 

 different depths of colour, to adapt it for use with an illumination 

 of greater or less intensity. Even with such appliances, however, 

 we are most of us aware that it is a matter of some difficulty to 

 obtain the best balance between the illumination of the object in 

 the microscope, and that of the paper upon which the drawing is to 



