CHAPTER III. 



PRELIMINARY DIRECTIONS ILLUMINATION ACCESSOEY APPARATUS 

 ACHROMATIC ILLUMINATOR GILLETT'S CONDENSER PREPARING AND 

 MOUNTING OBJECTS POLARISED LIGHT BINOCULAR INSTRUMENT 

 PHOTOGRAPHIC DRAWING, ETC. 



AYING selected an apartment 

 with a northern aspect, and, if 

 possible, with only one window, 

 and that not overshadowed by 

 trees or buildings : in such a 

 room, on a firm, steady table, 

 keep your instruments and ap- 

 paratus open, and at all times 

 ready for observation. A large 

 bell-glass will be found most 

 convenient for keeping dust from 

 the microscope when set up for 

 use. In winter it will be proper 

 to slightly warm the instrument 

 before it is used, otherwise the 

 perspiration from the eye will 

 condense on the eye-glass, and 

 greatly impede vision. When 

 you clean the eye-glasses, do not remove more than one at 

 a time, and replace it before you touch another ; by so 

 doing you will preserve the component glasses in their 

 proper places : recollect that if intermingled they are 

 useless. Keep a piece of well-dusted and very dry 

 chamois leather, slightly impregnated with the finest 

 tripoli or rotten-stone powder, in a small box, to wipe 

 the glasses. 



