MICROSCOPES 45 



an independent swinging arm attached to the same 

 support that carries the condenser sleeve. It may be 

 rotated and moved across the condenser by rack and 

 pinion to give oblique illumination. There is also a 

 ring attached to carry patch stops, and frequently 

 there is an Iris diaphragm above the condenser, which 

 may be used in the stage when the condenser is with- 

 drawn. 



Too much stress must not be laid on the distinction 

 here drawn between English and Continental practice, 

 as many English makers have adopted the Continental 

 pattern, in response to the demand for that style. The 

 excellent series of " London " microscopes made by 

 Beck are fitted with a horseshoe foot, and the Conti- 

 nental type of substage and foot has been adopted on 

 Ross' Standard Microscopes. Leitz, on the other hand, 

 is giving a claw tripod to some of his stands. 



The chief points for and against each pattern may, 

 however, be broadly stated as follows : 



Stability. The greater stability given by the tripod foot 

 and high axis is now generally recognised, and the 

 horseshoe is being increased in size or altered in shape 

 to approach it in that respect, but the small claw foot 

 adopted by some makers does not give the stability 

 of the original, on account of the lower point of support 

 of the limb. 



Compactness. The horseshoe foot is superior in this 

 respect, and permits readier access to the substage 

 mechanism than the large tripod. On this account 

 many workers prefer it for visual work, when the micro- 

 scope is not often used in a horizontal position. The 

 claw tripod shown in Figs. 17 and 18, is, however, almost 

 as convenient as the horseshoe, and has more or less 

 superseded the original wide -spreading pattern. 

 :* Substage Mechanism. The chief disadvantage of the 

 Continental pattern lies in the absence of centring 



