82 
Fig. 39. Mierospeetroscope after Abbe. Fig. 40. 
Section through centre-line Slit mechanism 
of the whole instrument. (Plane. Full size). 
(V2 full size.) 
The apparatus is inserted into the tube in place of the 
ordinary eye-pieces and is clamped to the former by means of 
screw M in such a position that the miri-ors A and 0 serving 
to illuminate the comparison prisms and the scale of wave-lengths 
are simultaneously illuminated by sun-light. (Fig. 89 and 40.) 
In case, including a set of lithographed scales for recording obser- 
vations 
*IVIicrO-SpectrO-photometer after ENGELMANN for quanti- 
tative micro-spectrum analysis, constructed on the principle of 
Vierordt's spectro-photometer. In place of the eye-piece the 
casing A is attached to the body of the microscope by the tube 
R ; it contains two conaxial, independently movable slits in juxta- 
position, which are symmetrically opened and closed by right 
and left handed screws. The width of each slit is read off accu- 
rately on the drums T and T' to 0.01 mm and may be estimated 
to the approximation of 0.001 mm. The one slit is occupied by 
the image of the object under investigation, and the other is 
illuminated by light from the source of comparison, which is 
