234 
TYPHOID FEVER IH DISTRICT OF COLUMBIA. 
Table No. 3. — Temperature. 
[In degrees, Fahrenlieit.] 
Year. 
Jan. 
Feb. 
Mar. 
Apr. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Normal 
30.7 
30.4 
41.6 
51.0 
62.8 
70.0 
74.6 
72.4 
66.4 
54.7 
42.8 
33.7 
1906 
37.6 
32.5 
35.1 
53.7 
63.0 
70.8 
72.7 
74.3 
The drainage basin of the Potomac extends into four States — 
namely, Pennsylvania, Maryland, Virginia, and West Virginia — and 
at Great Falls measures 11,400 square miles. It is crossed from 
north to south by a series of parallel ranges, which constitute part of 
the Allegheny system. In general, the soil in the basin is fertile and 
is under cultivation. In the mountains cattle raising and lumbering 
are the chief industries, while in the region of Cumberland enormous 
quantities of coal are mined every year. Scattered through the basin 
on the banks of the Potomac and its numerous tributaries are tan- 
neries of varying importance. In the larger towns there are manu- 
facturing industries of various kinds. 
The population of this area was estimated in 1900 to be about 
500,000, or about 44 per square mile. Of this population about one- 
sixth is concentrated in places of over 4,000 each. The distribution 
of the population and its relation to Washington will be best under- 
stood by reference to Table No. 4 and the map which accompanies 
this report. 
THE CHESAPEAKE AND OHIO CANAL. 
Skirting the Maryland bank of the Potomac from Cumberland to 
Georgetown is the Chesapeake and Ohio canal. It is built on the 
surface of the land, but becomes one with the river at two points, 
namely, for about 3 miles above Dam No. 5 and for about half a 
mile above Dam No. 4, and is carried over Conococheague Creek 
and the Monocacy River by two aqueducts. It is about 160 miles 
long and is constructed for a depth of 6 feet tlmoughout, but varies 
in width in different sections from 55 to 65 feet at the surface and 
from 31 to 41 feet at the bottom. The total fall from Cumberland to 
Georgetown is about 610 feet, broken by 74 locks. 
The canal has one intake at Cumberland and is fed at six addi- 
tional points in its course. It will be remembered that the canal 
compan}^, to enable it to get water for this purpose, dammed the 
river at several points. It receives, besides, a few small streams and 
dry runs, but as a rule all streams pass beneath the canal through 
masomy culverts directly into the river. To prevent overflow 
sluices are provided which carry the excess of water directly into 
the river. At times of flood, however, portions of the canal are 
under water. 
The velocity of flow in the canal varies considerably in different 
sections, but is assumed to be about 1 mile an hour. A tide lock con- 
