ess
have on the community is becoming better recognized by students of
social progress, and there seems to be no doubt that spending money
on such features is not only desirable from the artistic standpoint,
but is justified on practical grounds as well. It is cheaper than to
create parks, when necessity and demand can no longer be resisted,
by buying property and occasionally tearing down buildings and
constructing _de novo._ That this work is now being done in
Washington, even after construction, is certainly a recognition of
the advisability of original efforts in this direction.

~George C. Whipple, M. Am. Soc. C. E.~ (by letter).--Mr. Hardy's
paper is an excellent presentation of the results of the operation
of the Washington water filtration plant from the time of its
construction in 1905 until June, 1910. Papers of this character are
altogether too infrequent, and the actual results from the filters
now in use are not readily accessible in detailed form. Yet it is
only by studying the results obtained by filters in actual use that
improvements can be made and the art advanced.

Among the many important facts brought out by Mr. Hardy, only a few
can be selected for discussion. One of these is the operation of
filters under winter conditions. It is well known that the
efficiency of sedimentation basins and filters is lower during
winter than at other times, yet it is just at this season of the
year that there is the greatest danger of typhoid fever and similar
water-borne diseases being transmitted by water. Most of the great
typhoid epidemics have occurred during cold weather, and the very
use of the term "winter cholera" is of significance. Apparently,
typhoid bacilli and similar bacteria are capable of living and
retaining their vitality longest during that season of the year.
Just why this is so, bacteriologists have not satisfactorily
explained. Doubtless many factors are involved. Because of the
increased viscosity of the water, sedimentation takes place less
readily at lower temperatures, and inasmuch as sand filtration is
partly dependent on sedimentation, the efficiency tends to fall off
in cold weather. During winter some of the external destroying
agencies are less potent, such as the sterilizing effect of
sunlight, and the presence and activity of some of the larger forms
of microscopic organisms which prey on the bacteria. Another factor
may be the greater amount of dissolved oxygen normally present