J.W. Powell's Survey of the Rocky Mountain Region. 345 
from these stations the altitudes of all located points were de- 
termined by the latter method. 
Instruments. Base-measuring Apparatus. — The apparatus 
used in measuring the base lines from which the primary trian- 
gulation is developed consists essentially of wooden rods aligned 
and leveled on movable trestles or tripods, the contact being 
The line of coincidence is marked upon both plates and contact 
is determined by a magnifier. A delicate spirit-level is attached 
to each case to adjust it horizontally and a thermometer inserted 
to determine the temperature of the rod. Two steel pins by 
which the rods are aligned are fixed on the cases directly over 
the center of the ends of the rods. 
which a sliding cross-piece is clam by thumb screws. 
Above this cross-piece parallel to and carried with it, is a sec- 
atheodolite. The line is first ranged out and stakes set 500 
feet apart along its length, then with six men to work the appa- 
ratus, 3,000 feet per day can be measured with all the accuracy 
d. 
Theodolite.—The theodolite used in the triangulation is of a 
new pattern, embracing a number of improvements demanded 
by the character of the work. So far as possible the number 
