86 
ELEMENTARY CHEMICAL MICROSCOPY 
of the radiant. To obviate this defect Tassin has devised an 
apparatus in which the radiant — either a small tungsten lamp 
or an acetylene burner — is attached to the illuminator mount¬ 
ing and hence in focusing, both radiant and illuminator are 
displaced simultaneously an equal amount; thus no realign¬ 
ment is necessary. The construction of this device will readily 
be understood by referring to the diagram, Fig. 37. An ordi¬ 
nary disk (or prism) illuminator I is attached to the tube T of 
the microscope. Into the lower opening is screwed an aluminum 
adapter A which serves to hold in position the supporting bar 
B. The objective 0 is screwed into the lower end of A. The 
bar B carries a vertical sleeve J, fitted with a thumb-screw and 
serving to hold in place the remaining parts of the illuminator. 
The sleeve D carries a Ramsden eyepiece, securely held in posi¬ 
tion by the screw K. This eyepiece acts as a condensing lens. 
The correct position of the lenses to obtain a spot of bright light 
of the requisite diameter upon the reflecting surfaces is secured 
