ARRANGEMENT OP APPARATUS, ETC. 101 



The largest hole of the diaphragm is turned till it 

 occupies a position approximately in the optic axis of 

 the microscope. The plane side of the mirror is 

 brought as close as possible to the stage of the 

 microscope, without interfering with the motions of 

 either itself or the condenser. 



The lamp should now be brought near the stand, 

 on which it rests, (i.e., as low as possible), by the rack 

 and pinion movement attached to its back. 



Our reason for keeping the lamp low and the 

 mirror high, is, the greater the angle made by the 

 incident and reflected rays, the better the illumina- 

 tion. 



The light from the lamp may be thrown on the 

 condenser by altering the inclination of the mirror, 

 the eye at the same time being applied to the eye- 

 piece. 



Still looking through the microscope, the pin hole 

 cap is brought into focus, and centred, by turning 

 the screws in the rim of the substage tube. 



When central, the diaphragm plate is turned till 

 a medium-sized hole is under the condenser; this 

 aperture is now brought into focus by increasing the 

 distance of the objective from it, and made coinci- 

 dent with the optic axis of the instrument, by dis- 

 placing the diaphragm wheel sufficiently in its own 

 plane. 



This being accomplished the flame of the lamp is 

 focussed, by altering the distance between the top of 

 the condenser and the objective, (in other words by 

 using the coarse or fine adjustments of the micro- 



