134 



PEACTICAL TREATISE ON THE MICEOSCOPE. 



object which it is wished to obtain, the finger is to be quickly 

 removed and as quickly replaced ; the moment the finger is 



Fig. 87. 



Fis. 86. 



taken off, the atmospheric pressure will force the water, and 

 with it, in all probability, the desired objects up the tube; 

 when the finger has been .replaced, the tube containing the 

 fluid may be withdrawn from the phial, and as the tube is 

 almost certain to contain much more fluid than is requisite, 

 Mr. Varley adopts the following plan for getting rid of the 

 excess. 



Being provided with some watch glasses and some pieces of 

 plane glass, if the tube should contain more fluid than is neces- 



