158 MICROSCOPIC ILLUSTRATIONS. 



and thus chemical actions of all sorts may be studied under 

 a magnifying power. 



Moreover, the stage must be enabled to shift down to 

 the end of its bar, so that we may use object-glasses of 

 long foci, arid also place any large bulky body upon it 

 without building up the whole instrument to an extrava- 

 gant height, and thereby rendering it top-heavy ami 

 rickety. It must also be of such strength as not to spring 

 under the weight of our hands when used for dissection ; 

 for if it does, it will be utterly impossible to preserve a 

 steady focus, which will be found a dreadful nuisance 

 with a high power, and indeed with any power. Its size 

 must also be such as to afford a sufficient support for the 

 hands. The distance of the hole in which the slider 

 holder is fixed from the bar, must also be such as to allow 

 a slider to turn completely round, otherwise we cannot 

 get test objects into that position relative to the light in 

 which only they can be demonstrated. (This is especially 

 the case with the markings on the scales of beetles and 

 butterflies.) 



I do not much approve of attaching illuminators to the 

 stage, either for opaque or diaphanous objects. It will 

 be found much more commodious to cause the spectrum 

 for opaque objects to travel along with the body. Accord- 

 ingly, a condenser should be attached to it. Both the 

 mirror and condensing lens under the stage should be 

 caused to swing round by means of a spring socket and 

 pinching screw working on a round bar, so that they 



