46 
ENGINEERING: H. L. ABBOT 
An inspection of these tables shows a satisfactory correspondence 
between the observed annual rainfall and the outflow and river oscil- 
lations as indicated by the number and duration of the freshets. There 
is, furthermore, a suggestion of a tendency to a progressive annual 
change between years of maxima and minima in these quantities, 
which is worthy of notice. If future records confirm this suggestion, 
it will be needful to study the reason for it, as is now the case with solar 
spots, aurora borealis, and other natural phenomena. As to the second 
table, it must not be forgotten that it covers a period when the area of 
the lake was gradually increasing, causing a variable loss due to evap- 
oration. The values given for it for the last three years are taken from 
the official reports, and are based probably on direct measurements. 
The tropical conditions of the Canal Zone are so different from those 
in the Continental United States that it is interesting to compare them. 
This may be done from Rafter's tables, in his valuable paper published 
as the Water-Supply and Irrigation Paper, No. 80, of the Geological 
Survey. It is done in the following table. 
Average Rainfall, Run-oef, and Difference 
WATERSHED 
AREA 
SQUARE 
MILES 
PERIOD 
YEARS 
RAIN- 
FALL 
INCHES 
LOS 
By Outflow 
SES 
By Evap. Etc. 
Inches 
Per cent 
Inches 
Per cent 
Muskingum River 
5,828 
8 
39.7 
13.1 
33 
26.6 
67 
Genessee River 
1,070 
9 
40.3 
14.2 
35 
26.1 
65 
Croton River 
339 
23 
49.4 
22.8 
46 
26.6 
54 
Lake Cochituate 
19 
38 
47.1 
20.3 
43 
26.8 
57 
Sudbury River 
78 
26 
46.1 
22.6 
49 
23.5 
51 
Mystic Lake 
27 
18 
44.1 
20.0 
45 
24.1 
55 
Neshaminy Creek 
139 
16 
47.6 
23.1 
49 
24.5 
51 
Perkiomen Creek 
152 
16 
48.0 
23.6 
50 
24.4 
50 
Tohickon Creek 
102 
15 
50.1 
28.4 
57 
21.7 
43 
Hudson River 
4,500 
14 
44.2 
23.3 
53 
20.9 
47 
Pequannock River 
64 
9 
46.8 
26.8 
57 
20.0 
43 
Connecticut River. 
10,234 
8 
43.0 
22.0 
51 
21.0 
49 
Chagres River 
779 
21 
118.1 
82.1 
69 
36.0 
31 
Gatun Lake Basin 
1,320 
6 
119.4 
75.0 
63 
28.3 
24 
An inspection of the last four columns will show how much more 
favorable to the operation of a canal are the hydraulic conditions pre- 
vailing upon the Isthmus than those existing near the Atlantic Coast 
of the United States. Considerably more than double the volume of 
rainfall is available, and the losses from evaporation, plant growth, 
