Notes. 



293 



not differ greatly from the preceding model ; the ring was made thinner, 

 and the rotating stage mounted in the same plane as the ring ; as the 

 substage is entirely detached from the stage, it does not rotate with 

 it. The difference between Powell's concentric rotating stages and 

 those of Ross, is that Powell's are capable of complete rotation through 

 the entire circle, while those of Ross can only be rotated through 

 about 3/4 of the circle, as the limb fouls the heads of the pinions 

 of the rectangular movements of the stage. 



This rotary stage is beautifully finished ; it is a conical movement 



Fig. 83. 



