224 HOW TO SEE WITH THE MICROSCOPE. 



cess, and get good shows of the lepidoptera, I recom- 

 mend that he practice for some half-dozen sittings over 

 the same mount. By this he will get a certain familiarity 

 with the instrument which will be of great value to him. 

 The chances are, too, that he will wonderfully improve 

 in the manipulations, and in this alone will be well 

 enough rewarded for his pains. Furthermore, he will 

 learn what nice effects can be had by the slightest changes- 

 in the position of the tube, glass disk, shutter or lamp, 

 and the necessity for the closest focussing will be taught 

 practically. 



Having thus got tolerably acquainted with the instru- 

 ment, let the operator try changing from reflected to 

 transmitted light, and vice versa, which is accomplished 

 merely by moving the lamp back to its first position, 

 employing the mirror just as was recommended at the 

 start. A little practice of this nature, working alter- 

 nately by transmitted and reflected light, will soon 

 accustom the observer to the situation, and enable him 

 to make the change in illumination almost instantly. 



A fact worth knowing is this : The combined length of 

 the illuminator and objective will, if the objective selected 

 be one of the extremely long models, defeat its use 011 

 some of the smaller stands. Thus we find that we can- 

 not use the illuminator with a Tolles one-sixth or one- 

 tenth on the little " Histological" of Mr. Zentmayer, 

 there not being sufficient room between the "jacket'* 

 in which the body tube slides and the stage to receive the 

 illuminator and objective when coupled together. We 



