METHOD OF PHOTOGRAPHIC SURVEYING. 515 
plotting of the glacier we have its average slope, which in this 
case is 1:3. From points treated in this way we obtain a mean 
fall for any particular point during the twenty-nine days of 11.2 
feet, being equivalent to a motion of 33.6 feet. 
For comparing the azimuths of the same point in two photo- 
graphs we refer the point in each to the same vertical through 
some point on the mountains—(the verticals drawn for the pur- 
pose of ascertaining the shrinkage were utilized). The linear 
measure taken on the photographs combined with the fixed focal 
length of the camera gives the desired angular differences in 
azimuth, and this latter applied to the known distance of the 
point gives the motion of the point at right angles to its direc- 
tion from the station. The quantity expressive of the above 
motion must be corrected for the actual direction of the point. 
This latter direction we again obtain from our general plot of 
the glacier whereon the direction of ridges is established. 
For eighteen points change of azimuth was thus determined, 
and from the relative position of the station to the glacier front the 
change in the absolute azimuth of a point changed from minus to 
_ plus, those to the left or west decreasing, those to the right or 
east increasing in azimuth, while those directly in front, z. ¢., 
where the direction from the station to the point was coincident 
with the line of motion, showed no change in azimuth. From 
these we obtain a mean absolute motion of 29 feet, which, com- 
bined with the above, gives a mean motion of a fraction over a 
foot per day from July 13 to August 11. From this data alone 
it would be imprudent to give an estimate of the total motion 
in the year. The greatest distance of any point considered was 
about 3000 feet from the station. 
The results obtained may be summarized: 
Between July 13 and August 11, 1894, the end of the Baird 
Glacier was lowered by melting a little over two feet, and the 
average motion of the ice in that part was one foot per day. 
The Baird Glacier consists of two arms, each about 16 miles 
long. About one and three-quarters miles from the terminal 
moraine they merge into one stream. At the western side 
