48 
LANGLEY. 
tion of the fixed reticule (shown independently as it appears 
to the observer and of full size in figure 2.) 
Full Size 
S.P. Langley. snvt 
e e are the lenses of a positive eye-piece. I is a lamp for 
giving wire illumination, if desired, when a telescope is em¬ 
ployed. 
Field illumination is readily obtained by making the dia¬ 
phragm in which the prism p is set of translucent material. 
Finally it should be remarked that on removing the eye 
piece, events may be observed without using any telescope. 
In this, its simplest form, the chronograph may also be dis¬ 
pensed with, and the record of the second made on an at¬ 
tached stop-watch dial, and the instrument may thus carry 
