, 1879-05-17
SPARKS OF SCIENCE,
TIL; DEPOSITION uF DEW.
To TIT Editor ot 7he TRIBUNE.

TIL; DEPOSITION OF DEW.
To tn Editor oj 7he Tribune.
CHICAGO, Stay 15.-slnce writing the artlclo
published in your issue of lite 10th inst, havo
received pamphlet from Prof, stocxhrIdgc, os
the Massachusetts Agricultural College, Am.
hcrst, containing Ills report un and the result Of
agrcat number Of experiments nat!c during The
months Of Mav to HovcInb CT, Inclusive, and
from whcl, experiments ac tncIines towards
conclusions. other than those held hv scientists
generally, md ns supplementary to what have
already written on tf,i. subject desire to aub.
nit tic followtnKpartIat review Of his reputt:
Ttof. Htockbrlge, II / understand him right,
concludes tlat The deposition OF dew Is tle re.
suit Of moisture rising from or lu the grolad
to itn surface. where IL meets or coulcs III co,i-
tncf with the colder atr. ns llu clnH, tmme'if-
ntciy at tllc auitace OF thu Nrou.id. a1Ht Is de-
posted there rs dew. In support 1f this theory
be cites the result Of numerous experiments.
LIT u. examine these briefly.
He gives The average result of large number
Of experiments from Mar II November In.
ti,at the generally nceepsod theory Of the cool.
inE down Of the earth at night to q temperature
below TINT of the air is susceptible Of a titlEe
n1odftlcalt0n for he sayA TINT in nearly a1l OF
these experiments he found the soil In the
morning seycral degrecs warmer than :hc air
abovc.
In regard to this, observation has taught mo
That there are 50 liianv conditions :lsat affect the
tcmpcrnlry OF the soil and air that such expert
nents candot be 1u1ly relied OIL a+ proving or
dfsprorlng either the theory Of rEof. Siockbr!dye
or The moro generally accepted theory Of DR..
Wells, alluded to In my former contnuutra-
tion.
hayo myself made similar experiments over
nnd hytt ngain, ut,d OH the sane ground, nlld
with very varying reaulss. in Inost cnses have
found the .nrfacc OF tho earth to beg,n
n snf1t 1utu<Yk ft,r t<1 frIx
weather: and sometimes to run down =
or 10 degrees even br q or 10 o'clock, but
generally from T to 10 degrees ~ and during
the night below that ct ts or. but IN II trial
made this morning (s!ay I5) the soil Of tho sar-
face IL degrees higher than that Of the u[s four
feet nboye tho earth.
The past night WAS clear, the ground moist
frou, rnn-fail no doya before, tlAc air still,
poeit the result. But my observations of tho
temperature of air aud Bufl Inns been almost In
yaEiablF ttle rcrcrscs VI what Indicated this
morning. SO that, taking Into tho account the re-
others, as well ns my own, l MI clearly Ut the
opinion TINT the deposition Of dew DOES nut t!c-
peul wholly on nn excess Q! temperature III
either the earth or soil, but that II the air,
whether BY radiation Of ltat from tie earth or
otherwise, oscomes cooled down to whut
Is known as the lew point, H. will
deposit its moisture on the earth Of other tcrreS
trial things, but certainly tlo not share In the
lng process takes place as tlle grosnd surfaces.
His experiments with t1lr tin cans f1Iled with
soil, BY which slc found deposition III moisture
dew On the undersdo of the coycs aud not un
the upper side. carrles evidence, to my tDiul,
Of the correctness OF incorrertMcss Of either
theory, nor docs the fact that, when a hay cock
ls removed from the gr0und On which it has
stood over night, 1t Is always found wet unduT-
the ground IL both MORT nnsl wnrns It sends UT
its heat and vapor together tuto spacc, and II
Eay.rork OF mowers Whutstone, to which hs
refers, board. or other substance shns cover
vnpor In Its upward course and It will be Do
posted underneath them In tho form OF con-
densed vapnr OF wntcr, Just the san.u ns The
atcu.n would candenau ot, tic under alr of the
cover uf our dnnrr.pot wl,en boiling oycr lire.
The metal cuycs to tue tin cat. that Prot.
StockbridEe used was, rs Prof.. Tynlatl asserts,
''ppor radiator" hence, as MelouI and others
have found tn similar experiments. Its temper
attire mas higher than the air In contact With 1t,
and would not 10 instrumental In conaenstug
tho molsture tn tllr a!r that came In contact
With it; therefore no dew would necessarily bo
deposited thereon, but, like thu hny.cDck, 1t
covered certain portlun OF the earlh's surlace,
und, 'tKe the cover to tho pot n{su WIS IN the
way Of the free passage OF the rising moisture,
ala, Us u matter Ut course, would Intercept md
conlcnsc II then and there Without reference to
which was the coIdest. provided the mir wss be-
low the dew po.ut. ucIrc wn u,ny conclude TINT,
With dry soil nnl atmosphere tiI. enrth Mill
30 far rn!ate IT, heat Into space as to reduce Its
na n by .ia HS' ,s below nj, the .brs dew
It, and to coneuse tho yapor held IN susuen-
sion BY tho ar, md dew will o. ue,o.ted: but
II TIC soil and other terrestrial aubstanccs be not
sufficiently reduced In temperature to to tllEs,
ii 1t be higher than that Of tho air immediately
IN conlnct with It. observation shows cunclu-
siycly TINT dew will be deposited notwlttstA'nl-
lug. Otherwise why do We f1lld heavy depost
Of dew Often congcalcd Into hoaF froat Oh tile
roofN of mir hougik. f,u the tons of Ullr ttces.
etc! couecivo this latter phc1lon,e1a concl,t-
siyo as against the theory that duw Is deposited
at the surface OF The soil. There can bu no
question t!iat Tapor rises through tho pores and
arteries tn tile soil and passes Into the alr; then
1t dEffuses itself 1ikc other vapor, nnd then
cooled BY any ca,,se, whether II b. " the nhu
cnce of cold win!s, OF BY contact With thu Garth
or other terrestrial things lhHt have rasliutctl
their heat in<o space, u will By condensed us,l
p5oein'tatsda It'd ss dew, and II told enough 1t will
Tile experiments OF 'rof. Btockbridge, which
were evidently male With great deal Of rnru
nnd with dcstro Only to cfi.n!hata the truth
without refercnre to whose theortc6 should he
ycry different rcsul.a would be obtained On
different soils, mud also tn the 6ntnu snila ut
different tllnos, depending OH tllc trnappraturc
Of the Garth, air, a,d especially Of thu winds.
The onc grrnt pr,nc!pls that u 30 apparent iu
t!un OH tho outside Of all i.H-ptchcr III warm
weather, a,ld un thu inside vi d pane Ut Windows
glass ia cold wcatict Is cttnr1t1syo evtenre that
dew Ii tlsu result Of contact OF air with cul!cr
bodies, aud thu dow and frost OIL the roofs Of
cur houses is just as conclusive that other cou-
dtions than those Of vlnor rising froul the
q. +. RANDALL.
CONCERNING AylKsrIIETICs.
fastsp Journal nf fMemtslFv.
It ID not merely patt aa such Whiel, No seek to