40 ILLUMINATION. 



board is attached to give rigidity; this board 

 is fastened by screws to a block which can be 

 raised or lowered on the pillar D by rack and 

 pinion movement. A lateral motion is communi- 

 cated to the pillar D by means of the screw F. 



The lid of an oblong tin box abcut one inch wider 

 than the chimney of the lamp, has a hole cut in it 

 of sufficient size to allow of its fitting tightly 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 turned down hori- 

 zontally. 



Another round hole two inches in diameter, is cut 

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

 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, 

 allow a current of air to circulate between the 

 mirror and the chimney of the lamp, and prevents 

 their cracking. 



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 

 ^o this, full information will be supplied by any 

 leading electrical firm. 



