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SUMMARY OP CURRENT RESEARCHES RELATING TO 



Microscopes, and is thus specially adapted for dissecting, examining 

 large sections, &c. The tube has an interior diameter of 29 mm., 

 and the apparent diameter of the field measured at a distance of 

 250 mm. by means of the camera lucida is 200 mm. With the 

 ordinary Nachet No. 1 eye-piece this diameter is only 135 mm., and 

 with No. 1 Prazmowski 110 mm. There is a variable objective, which 

 when shortened gives a magnifying power of 15 with a working distance 

 of 28 mm. and real diameter of 13 mm. When extended these figures 

 are 23, 7 mm. and 8 • 5 mm. respectively. 



Stephenson's Aquarium Microscope. — This Microscope (fig. 128) 

 was designed by Mr. J. W. Stephenson for the examination of living 

 objects in an aquarium. 



Fig. 128. 



A brass bar is laid across the aquarium, as shown in the woodcut. 

 To adjust it to aquaria of different widths the support on the left is 

 made to slide along the bar, and it can be clamped at any given point 

 by the upper milled head. The milled head at the side, by pressing 

 on a loose plate, fastens the bar securely to the aquarium. 



Between the ends of the bar slides an arm carrying a sprung 

 socket, and the arm can be clamped at any given point of the bar. 

 Through the socket is passed a glass cylinder, cemented to a brass 

 collar at the upper end and closed at the lower by a piece of cover- 



