The daily critic., 1890-11-06
THEORIES EXPLODED BY SCIENCE.
Merely The E1udatiOn Of Watsry
Juices Of Healthy Vegetation.
SOME INTERESTING EXPERIMENTS.
Eow Mother Earth Refreshes the Thirsty
Plants and Difuses Fragrance
All Around for Mortals
Benefit.

IL, on summer evening, after the
twillghts peaceful reign had succeeded
the sway Of the brilliant sunshine, YOU
asked one what was on your boots OF
trousers as you sped through the glisten
ing meadow, studded with its lowing
kine, you would be told-the dew. If
on bright morning, when all natur,
was awakening from her balmy night
rest, you inquired about the diamond
drops that in millions sparkled on this
mountains brow, the uniform answer
would be-tbe dew. And If, on a visi
TO the garden, you see on the broccol
large, clear drops. translucent with gold
light; or 10 the field, you see on the
turnip blades crystal drops all a.trembC
with immaculate brilliancy, you would
conclude that that Is also-the dew.
Now, that Is not dew at all SAYS J. G.
Mcpherson In "Longman's Magazine. -
In all Of these cases, where ninety-nine
OF every hundred intelligent people
would dogmatically assure you of the
long. cherished and undisputed opinion,
the answers are wrong. Ruthless sci.
enCe has driven the sentiment out Of the
poetic mind
a#a
The exoretion of water by healthy,
growing leaves has been long well
known. The crowuing merit of this
discovery Is due to the most indefa.
tigable and marvellous perseverance,
amounting TO genius-of Mr. John
Aitken. f. r. s., Of Falkirk. He has
conclusively proved that what has been
so long called dew is merely the exuda
tion Of watery juices Of the healthy
vegetation. In the course Of his pains
taking investigation he selected a small
turf, placed over II a glass receiver and
lelt II TIL drops were eNcreted. Remov
ing the receiver, he selected blade hav
ing drop attached 20 It, He dried this
blade and inserted its tip into a small
glass receiver, sD as 10 Isolate IL from
The damp air Of the larger receiver
The open end Of the small receiver was
closed by means of very thin plate OF
metal cemenied TO t.
In the centre OF this plate was pierced
a small opening TO admit the tip Of the
blade; but the opening was then care
fully made air tight by means OF an
india.rubber solution. After time,
though this blade was thoroughly iso
lated, he saw that drop was formed
on the tip, OF the same size as the drops
formed on the blade under the large
receiver. He, Of course, was entitled
10. conclude that the drops on the out
side blade, as we'll as on the Isolated
blade, were really exuded by the plant,
and not extracted from the air. Mr..
Aiken next observed that these excreted
drops are formed on grass on other than
dewy nights. After rain, II there be no
wind, and the air near the ground Is
saturated, most OF the blades were found
10 be tipped with a drop at the same
point as the exuded drop appeared at
night. a position which no falling rain
drop could keep. This experiment Is
so easily made by any one, that the in
teTest and the information gained are
ample reward for the little trouble taken
in making It.
-
What has been for centuries called
dew Is not dew at all, but the watery
juices Of the healthy plants. But look
over dead leaves and you see fine
pearly lustTe-that is dew Dead mat
ter gets equally wet where equally ex
posed, and the moisture does not c)l.
leci on II in regularly placed drops as Il
does on plants. If radiation continues
after the sap drops have been forming
for some time, the dew makes its az.
peaTance all over the surface. But
whence com es the dew Acute ob
servers saw that the dew clad grass was
chillier than the air above. In the be
ginning Of the seventeenth century,
NaTdius of Florence defined dew as an
eXhalatiOn from the earth Boyle de-
tecttd that the dew on gla- was formed
by the precipitation OF the Eapor OF the
air upon a colder body. Ia 1888 Ger.
steD assumed the authorship Of the
theory hinted at by Nardius, that dew
rose from the ground. But II was left
10 DT. Wells TO converge all the rays Of
scientific light upon the subject, aud
express In a clear and unambiguOus
manner the theory which, until about
four years ago, has been in It's entirety
adopted by scientific men.
According 10 Wells, dew was con- |
uensed out of the air near the surface Of |
the earth. His famous work, the /
Essay on Dew, was published in 4
1874 The great advance accomplished |
by DIR. Wells was 10 show that the I
Of dew on any night, OF on any /
body, depended on It's powers of Tadiat- 1
ing heat az the time that the more a |
body was cooled by radiation, the more I
dew Il collected that, Ia fact, dew was /
simply a case Of condensation of the /
yapOr In the atmosphere; and tnat, |
therefore, body, before Il got deWed. I
was cooled BY radiation 10 a tempera-
lure below the dew point at the place
But there was one thing wanting, that /
" hich he spoke Of az times very inded- |
nitely, the decided recognition Of the /
dew which rose from the ground This 1
development was left 70 another man, /
an equally distinguished observer. a |
practical physicist Of whom Scotland /
mas good reason 10 be proud.
-
Alr Aitken challenged Dr. Wells /
as 10 the source Of the
vapOr that condenses on the FadiahHg /
surfaces in the formation Of deR He
was struck with the unyaBing fact that
he ground, q little below the surface,
was warmer than the air over IT, So
ongl then, as the surface Of the ground
Is above the dew point yap0r must rise
and pass from The ground into the air
he moist air so formed viii miugle with
be air above it. aud its moisture viii /
De condensed, forming dew wherever #
lOmes In contact Wilh a surface cooled /
below the dew point In order b test
bis Hypothesis, Mr. Aiken placed over