J. H. Lane on an Automatic Comparison of Time. 45 
An arrangement suitable for carrying the above plan into 
effect is illustrated by a sketch in the accompanying plate. At 
the station A, the rays of the signal light, diverging from their 
source L (Plate II, fig.1, a), are converged by a lens C so as to 
meet and cross each other in the focus F of a telescope. Diverg-. 
ing from this point they traverse the object glass O, and issue 
from it in a nearly parallel beam directed to the station B. The 
light thus transmitted is periodically intercepted at the focus F 
by the projecting teeth of a rotating disc, or signal wheel, S, 
which is made to rotate uniformly at the rate of one revolution 
in about one second. 
The telescope used at the station B for viewing the light 
shown at A, is furnished with a terrestrial eye-piece, and at that 
point where occurs the-first image of the object glass, or crossing 
of all pencils of light that can pass through the telescope, is in- 
troduced a refracting glass prism P, shown in section in Fig. 1, 0. 
The pencil formed by the light from A, on traversing the re- 
fracting prism, is turned aside so that the star image, which 
otherwise would be formed at s, is formed at s’, and the dis- 
placement is observed by the eye at E. Since this displacement 
ow also the simultaneous angle of position of a 
