complained of as having no working distance (that the 

 objective could not be focused) when on investigation 

 it was found that very thick glass had been used as 

 cover glass. 



There is no question about the desirability of a long 

 working distance in the higher power objectives, as the 

 comfort of working is greatly increased and the danger 

 of injury to the objective and also the object which 

 may sometimes be a rare specimen is further removed ; 

 but, unfortunately, the difficulty cannot be eliminated 

 and must be reckoned with. It is therefore important 

 for the student to know the amount of w r orking distance, 

 so as to make allowance for it in focusing the objective, 

 and to know the limit of thickness to use with high 

 power objectives. 



The actual measurement of wwking distance in 

 microscopes having a graduated micrometer screw is 

 simple and may be determined as follows : 



Lower the eyes to the level of the stage and bring 

 the front of the objective very carefully just in contact 

 with the top of the cover glass. Note the division on 

 micrometer screw and by an upward focusing turn of 

 the screw bring the object in focus a/id read off the 

 distance traversed. 



With an oil immersion objective follow the same 

 process by bringing the objective in contact with the 



