346 JW. Powell's Survey of the Rocky Mountain Region. 
a 
inches in diameter, and reads by double verniers to five sec- 
the scale adopted by the 
é ry for 
Interior Department for the hysical atlas of the Rocky Moun- - 
eo region, that is, a scale of four miles to the inch. 
ments of its optical axis are recorded. The telescope rotates 
about a vertical and about a horizontal axis similarly to the 
telescope of a theodolite, and is connected by simple mechan- 
ism with a pencil which rests on a sheet of paper attached to 
the platen. When the topographer moves the telescope so as 
to carry its optical axis over the profiles of the landscape, the 
pencil traces a sketch of the same. This sketch being mechan- 
ically produced, is susceptible of measurement, and is a definite 
and authoritative record of the angular relations of the objects 
presses Co loeeh cetre ae gee eaeea 
