PHOTOGRAMMETRY. 



599 



concerning- which the following particulars are obtained. Camera 

 upright ; focal length, 8Un. ; and horizontal distance from midcile 

 of lens to post, 68ft. 9in>' 



By reference to the accompanj'ing wood-cut it will be seen that 

 the space between the horizontal line and the ground scales 78 

 units, and the space from the same line to the top of post 19(» 

 units. Thus there are two sides of two right-angled triangles 

 from which to find one angle of elevation, and one of depression. 



Measured with ; 



tape, for calculating; height of post after the angles have 

 been found. 



