106 THE CANADIAN NATURALIST. [Vol X. 



prism underneath, and to one side of the stage. I was surprised 

 at the brilliancy of the effect produced, and concluded that if so 

 brilliant an effect were produced by oblique rays from one point 

 only, much more brilliant would be the effect if I could procure 

 a condenser that would throw a complete circle of oblique rays on 

 the object. I took my small bull's eye condenser of If in. diame- 

 ter and 1 in. focus, placed on it a disk ^ in. diameter, capable of 

 being raised or lowered, and by means of an adapter placed it in 

 my substage, using the flat mirror and either the 1 inch or 2 inch 

 objective. I obtained an effect (pirticalarly with the inch ob- 

 jective) which surpassed my most sanguine expectations. In trans- 

 parent tissues such as the maple leaf insect, there were clearly 

 revealed lines and structure that could not be seen otherwise, and 

 in insects partially transparent, a perfect Jiood of oblique light 

 with a dark ground was thrown on the structure, producing mar- 

 vellous effect and giving wonderful clearness of definition to 

 the finest lines. With my 1 inch objective I could see, on the 

 two minute lancets of the mosquito (having the saws at their 

 ends) running from root to the saw a beautiful fringe of exceed- 

 dinuly minute, long hairs, hooked at the ends, sharp and well 

 defined, having a dia. -g-Q-J-g-Q in. or .846(359^6. and set 11,000 to 

 the inch, which owing to their transparency I had never seen 

 before. The markings and rounded structure of Fleuraslgma 

 augulatum are seen with the inch objective and binocular. By 

 raising the disk the field is darkened, and by different focussing of 

 the condenser, various effects are produced. With this mode of 

 illumination, it is necessary to see that the flat mirror is in the 

 axis of the instrument. 



I placed on the centre of the disk a projecting pin which 

 enabled me to put and retain on it different plates or diaphragms 

 shutting out whatever portions of the circle of light desired. 

 As a condenser for high powers the apparatus described is un- 

 surpassed. I intend trying a condenser 1;^ in. dia., -J in. focus 

 with I" in. spot, in the hope that with still more oblique rays, 

 even a more brilliant effect will be attained. 



After some remarks irom Dr. Baker Edwards, those present 

 adjourned to the library, where a number of microscopes were 

 exhibited by members of the Microscopical Club, and by Mr. 

 Muir who showed the excellent results that could be obt lined by 

 his method of illuuiiuation. 



