230 



On A Method, of Equalising the Thickness op Slips when 

 using an Oil Immersion Condenser. 



By E. M. Nelson. 



(Bead Nov. 27th 1885.) 



It is necessary that an oil immersion condenser should have a 

 fairly long focus, otherwise it would be of no use if the slip 

 happened to be rather thick. 



If the slip is thin it will be found impossible to keep the oil 

 contact when the condenser is in focus, unless you increase the 

 thickness of the slip by uniting a thick cover glass to the back by 

 oil. It will be found very difficult to do this without oiling the 

 stage when the microscope is inclined. The oil between the 

 condenser and the cover glass is sure to unite with that between 

 the cover glass and slip, and then the cover glass falls, upsetting 

 the whole arrangement. I have found the following plan to answer 

 admirably : A piece of glass one inch square, upon one side of 

 which, close to one edge, a strip ^in. broad is fastened by shell-lac, 

 is oiled to the back of the slip ; the ledge hooking over the edge 

 of the slip prevents it slipping down. 



