93 



instruments provide more room between the stage and 

 base on the lower side and stage ana ^trrwfon the 

 upper, than do the Continental. 



As stated previously, a variety of stages are offered 

 on instruments of similar construction. The plain 

 flat stage while preferred to some, offers no advan- 

 tages over the ordinary round one, unless specially 

 made for examining specimens on larger slides than 

 the standard 3 by 1 inch. Some claim advantages for a 

 smaller stage than the length of the slide, so that this, 

 projecting, admits of the slide being grasped and 

 swung around the optical axis. These advantages, 

 however, are not generally appreciated, and even if 

 so, are offset by the drawback that in moving the 

 slide it is apt to be tilted. 



Spring clips are usually of similar construction, 

 although varying in detail and curves. Properly con- 

 structed clips should have such thickness of metal 

 and be so bent as to allow specimens to be brought 

 under them without resistence and keep them prop- 

 erly in place without too much pressure and conse- 

 quent friction. 



A glass-stage and slide-carrier may be considered 

 a good investment, as it admits of the convenient 

 manipulation of the slide without the grating feeling 

 which usually accompanies the direct movement of 

 the slide on the stage. 



Where systematic examinations of a specimen are 

 to be made, a mechanical stage will be found a great 

 convenience and in petrographical work is almost a 

 necessity. 



