Evening star. [volume] (Washington, D.C.) 1854-1972, 1897-10-02
OUR WATER SUPPLY
Interesting Field Meeting Of the
National Geographic Society.
PAPERS OF GREAT INTEREST READ
History of the Washington Aque-
duct and Its Novel Features.
POLLUTIONS OF THE POTOMAC

Threatening weather has very little effect
upon the members of the National Geo
graphic Society and their friends when
anything of interest to them is underlined
for enjoyment and the first field meeting
of the society, which was held this after
nc on at Cabin John bridge, was almost as
well attended as If the sun had been shin
ing in its most genial way.
The party in attendance assembled in the
pavilion near the hotel and were called to
order by President Gardiner G. Hubbard
who gave brief explanation of the pro-
posed plans of the society. Prof w. ]. Nc
Gee gave very interesting talk on the
development Of the geographic history Of
Cabin John Run.
Professor McGee's paper on the geo.
Professor McGee's paper contained a
beautiful description of the stream, and
then gave scholarly view of its work.
The work of Cabin John ran" he said,
like that of other streams, might be
measured by aggregate quantity, by rate,
or by time; and the measurement of any
two of these would give the value of the
third. The readiest measurement is that
of rate; and within the last year or two
the United States geological survey has
begun quantitative study of various
streams in the Potomac basin, streams SO
related to Cabin John run that the results
of the measurements may be applied to
this stream.
1.-THE work is not done: but the prelimi-
nary determinations indicate that through
cut the area drained by the Potomac the
rains and rivers are wasting the land and
carrying the debris seward at the rate of
about third of an inch per century. This
rate may seem infinitesimal; yet it IS with
such values that the physical geographer
has TO deal and from then, ffnt he
derives necessary ideas as to the vast pc
RODS of time involved in the processes of
earth making. This rate of third of sn
inch per century is mean value, appli-
cable throughout all seasons over q large
area; actually the rate varies from season
to season and from place to place.
THE widest variation is that from sun
shine to storm, when the rate may be
Temporarily multiplied n tnousand-fold,
perhaps ten thousand-fold. The next va
ration Is from steep slope to gentle slope,
whereby the rate may he multiplied hum
dred-fold or more, and there is wide varia-
ton with the size of the stream. These
and other variations have not been meas
ured. but they may be examined in a quail
itatiye way.
Variations That Are InstruetIve.
when SO examined the variations in
rate going with variable slope are found
particularly instructive. For example, the
lowering of the channel Of Cabin John run
beneath the noble bridge at the mean rate
Of an inch or two per year is several hun
dred times more rapid than the average
lowering OF the surface throughout the
area drained by the stream. It follows
that the local work is so far outrunnng
the general work as to demand special ex-
PLANTATION.
"A simple explanation is that the land is
rising so rapidly as to maintain a relatively
steep slope toward the mouth of the
stream, but that the period of this lifting
he Ian
permit the stream to deepen it's channel in
Its upper reaches; and this explanation is
found to be in accord with SO many facts
(which need not be detailed) as to compel
It's acceptance Accordingly thu stream
must be Interpreted, not merely as char
acter recording its own work, but rs a spe-
cially significant character recording also
general movements of the continent.
so picturesque Cabin John run is much
more than a simple lineament in dead
landscape; IT is a character in the record
OF earth-makinS, which, properly inter-
preted, tells of the making of it's own chan
mel, of the shaping of the land by slow
stream work, even of the mass movements
of the continent, and especially does it
tell of those vast lapses of time which stu
dents of carth-making are compelled to
recognize
Then came two contributions to To-
cal history. whose Importance is not con-
fined to any class of citizens but which
will be instructive to all.
Capt. d. d. Gaillard of the Engineer
Corps. U. s. A, had prepared a paper on
the Washington aqueduct and Cabin John
bridge. which was read by Mr.. Edwin b.
Hay Capt. Gaillard's paper gave COM
prehensiye history OF the establishment
ard development of the water supply of
the national capital, and closely described
the Washington aqueduct system as 1T ex-
lists today, which is, with but few modifi-
cations. that originally planned by the late
Gen. NJ. c. Meigs This interesting contri-
button to local history was as follows:
The water supply is taken from the Po-
tomac river at Great Falls, about fourteen
mics above the city. At this point a ma
sorry dam feet in width on the top and
2.S17 Feet in length, completed in 1896, ex-
tends across the river from the Maryland
to the Virginia shore. The water passes
from the feeder. under the Chesapeake and
Ohio canal, through the gate house and
into the conduit. which is circular in cross
Sc ctioh, and for the greater part of its en-
tire length Is o feet in diameter, and COM
posed either of rubble masonry. plastered.
or of three rings of brick; but where the
soil in which it was built was considered
particularly good the inner ring of brick
was omitted. and the diameter was feet
inches Where the conduit passes as an
unlined tunnel through rock the excavation
was sufficient to contain an inscribed circle
IL feet in diameter.
Long Water Tunnel.
1.-THE total length of the conduit and the
two by-conduits around the reservoirs Is
twelve miles. and its slope is inches in
5000 feet. Constructed by General Meigs
in connection with the aqueduct system
are five bridges. two Of which are unique
among engineering structures.
AT the distributing reservoir the water
passes into four cast-iron mains-aS", 36",