102 ARRANGEMENT OF APPARATUS, ETC. 



scope), and centered by altering the inclination of 

 the mirror. We now make the image of the flame 

 of the lamp itself, and that of its reflection in the 

 mirror placed behind it, coincident. This may be 

 done by giving a slight twist or tilt, as the case may 

 be, to the tin cover surrounding the lamp. The 

 bull's eye condenser is placed from £ to 2 inches 

 in front of and from the flame of the lamp, with 

 its convex side facing the microscope, and cen- 

 tred by observing the position of its image in the 

 microscope ; this will be known by its appearing as 

 a brilliant disc of light without flaw or spot, in fact 

 a regular sun, in the centre of the field of vision. 



We now remove the condenser from its tube ; this 

 is best done by racking back the objective, and un- 

 screwing the lenses from the diaphragm tube at the 

 object side of the stage, without disturbing the 

 diaphragm or any apparatus except those requiring 

 removal. If on account of their position they can- 

 not be removed in this manner; the substage tube 

 H, is unscrewed without altering the position of 

 either the diaphragm or mirror. The condenser can 

 then be easily taken out and the substage tube re- 

 placed, the same precautions being observed as for 

 its removal. 



All the apparatus required are now perfectly cen- 

 tral with each other. It might be thought that 

 keeping the condenser in the substage would be 

 superfluous, but by its aid the images of the dia- 

 phragm, lamp, and bull's eye condenser are ob- 

 served through the microscope, and all made 



