46 J. H. Lane on an Automatic Comparison of Time. 
ngement, by means of which the observer, without bate 
tion, that for instance which is shown in Fig. 3, the exact angle 
equivalent of a single prism cut into a large toothed wheel. E 
This wheel K, like P, takes its motion from H, and is so gearet 
that during all the intervals of time in which a passing pe = 
would encounter the refracting part of P, it will have free pe 
sage through one of the spaces between the pieces P’, P’, P’, &1 
which, during the alternate intervals of time, will in their tum? 
be interposed in the path of the il. Any flash of light, ° 
therefore, that escapes through any supplementary opening, a ? 
in the middle of one of the sixteen primary teeth of the sign® 
wheel, will, in traversing the telescope at B, be refracted by on® 
of the prisms P’ alone, and not by P. And if it be recollected 
that the several prisms P’ are in elfect parts of one prism, as dis 
