64 ROYAL SOCIETY OF CANADA 
and of a tracer, ©, the whole being mounted upon a drawing table 
accurately plane. 
The metal plate, DD, in which the eye holes are pierced revolves 
upon a horizontal axis perpendicular to the middle of the line joining 












STEREOSCOPIC APPARATUS FOR PLOTTING TOPOGRAPHIC PLANS. 





Fie. 1: 

the holes, the inclination of this line being indicated by a graduated 
are and vernier E. The distance between the holes is equal to the 
