40 



ILLUMINATION. 



of sufficient size to allow of ils fitting lightly on the 

 small flange below the tongues of the burner, and as 

 near as possible to the side of the lid intended for 

 the front, that for the back being turnd down hori- 

 zontally. 



Another round hole two inches in diameter, is cut 

 in the front of the box, at such a level that the flame 

 may occupy its centre. 



In the middle of the opposite side a slit three 

 inches long is made, the upper extremity of which is 

 cut again at right angles; the flaps thus formed are 

 turned outward and a plane silvered mirror fastened 

 between them. 



The spaces left at the top and bottom of the flaps, 

 allows a current of air to circulate between the 

 mirror and the chimney of the lamp, and prevents 

 their cracking. 



An ordinary plano-convex condenser, its plane 

 surface being turned towards the lamp, is placed 

 about one inch from the latter, (when high powers 

 are employed), and a stand to hold blue glass between 

 this condenser and the microscope, The stand is 

 unnecessary if the arrangement for obtaiuing a 

 monochromatic light mentioned on a previous page 

 has been carried out. 



When using Swan's incandescent lamp, the same 

 method of preventing extraneous light from reaching 

 the microscope, and condensing the available portion 

 on the object is employed. All batteries and appar- 

 atus for working it are best purchased, with regard 

 to this full information will be supplied by any 

 leading electrical firm. 



