The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1881-03-10
Interesting letter fre" Pr"ss"s"r
winston.

ISend IL To u.s.
Interesting letter from fr"se~s"'
winston.
Editors Dispdtch IL wooid DE e'''e un'
gracious In me not 10 make courteous ,ep'n
40 the inquiry Of your correspondent A.
IN this MORNINGS paper, Tor n sccou'ps'
MED by so pleasant note, anu y sos'a s
moreover, by your poteat edher%i e"uo's''
snent. ,,. y, the
Ru, really have nothing new on Tue
suh,ect OF the tides; aud i take up tnc
ouesiion reiuciautly, az " eoniesseuS
snmcwb,, involved. and the explanation, IN
she absence OF diagrams. g. nine .dilncuit.
To. me sly fir.t that am not iittle sur
c,,.sd ~ find, az have done fecentiy, mat
90 many thoughtful persons have trouble
Win the theory Of the tides. Some "can'
moi seev how the moon raises The tides al
all. aud say, perhaps, that The esfih's gravity
ough. 10 pull back the wster even the
moon should pull II up. Others, IKE your
CORES pendent, are puzzled by the oOune
tide, aud can't possibly understand now tuc
attraction OF the moon can make TWO .iues
ut the SAM time on opposite sldes III t"e
earih-bow the moons pulling one way eau
make the water rise In exacl'y Tue VpIor,o
direction. And others still stumple " tue
mioh,v sim in this matter OF tide-Ials'ns.
Now rs 10 the moon causing the tides ~
general. | am sorry 10 see your inlimatlon
that This i q question yet unsettled. FER
mil me to say Just a word or two on tbis
point.
II Is perfectly well known fact that the
tides and the moon do always 80 together.
This is indisputsbIe. Whatever difficulties
NAV exist as TO tides being higher IN souIe
nI,res than ia others and slower in reaching
some points than Others, yet The Tine OF
their occurrence IL any particular place l.
lived and definite No tide has ever cc-
curred here ia Richmond. venture 10 say,
except when the moon was III one OF TWO
posi,ious--either four hours and twenty
MINUTES after it had reached IT'S hl2hesl
point overhead or the same time aiter u nad
reached #, lowest point underneath. Can
this be chance coincidence! 30 Tor the
future: can tell the exact hour Of high
tide here. say on the h of July next.
Howf SImpy by knowing when the moon
will be at It's highest point overhead on that
day. Aud thus. in fact, the predictions are
made that are published every day in tue
I6sDufch. But is there any reason IN the
matierY Can any cdasOi relation be traced
between the presence of the moon and the
rising OF the water? reply that il the Law
OF 2ravit,ti0n holds good here-n every
body in the universe attracts every other
BODY, and il this attraction Is mutual, ana
varies with the distance. as that law de-
clares-then the moon OF necessity must
raise tides.
Fact and theory unite, therefore, and |
defereniially submit that, so far IRON Deing
an Unsettled question, the evidence Tor tue
moons causing the tides is about the same
in kind and degree as that by which we at
tribute the coming OF day ana night TO the
rising and setting OF the sun.
But let Us hasten TO the question pro-
pounded by "X.," and see If we can ac-
count for the tide on the side Of the earth
farhest from the moon.
To simplify the question as much as pos
sible, let Us take the earth TO be solid
globe 5000 miles in diameter, and covered
entirely BY water. Let us 0bliterate the
moon for the time being. and thir OF the
earth under all the other forces acting on 1t
tits own gravity, the sun, &c.,) rs perfectly
spherical, and moving along in q certain Or
bit around the sun.
Now, let us suddenly bring in the moon,
and locate il Just 100000 miles from the
earth's ceatre. The two attract each other,
according 10 our laws Of grayitaiiOn refer
red 10 above, and begin TO move towards
each other as far as other forces will allow.
For defnlteness, suppose that the earth's
centre carrying the whole solid earth with
itl moves Just 100 icet-tbis being what the
moon could do at the distance Of 100000
miles. But the water lust under the moon
is only 100000 miles of; this OF course
would by the law be mole attracted, and
being water, and free TO move for Itself,
would move farther, say l05 feet instead OF
100. The water on the opposite side OF The
earth Is PA, 600 miles off: 1t would not be
attracted so much; say IT would move only
95 feet instead OF 100.
Now look at the shape Of our globe; the
wafer next 10 the moon is evidently Just
feet farther from the centre OF the earth
than II was before-the tide has risen
feet; the water also on the other side i
just 8 feet fmther from the centre of the
earth than it was befOre-it is that much
"higher the tide has risen . feet on that
side also.
And thus are produced By the dibercntiot
action OF the moon on the two sides and
the cebtfe of the earth respectively the
double tide. The sun being almost 400
times as far of is practically almost as near
10 Que side Of the earth rs to the other, and
so his d;ferestio{ attraction is very slight,
and hence he does little in raising the tides
Possibly an illustration may be Of service
on the whole subject. Let US try heat, as
that obeys toe same law as to weakening BY
distance that applies 10 gravity. Take three
thermometers and tie them crosswise 10 a
yards,iek, Que at each end and one IN the
middle; suppose that all the thermometers
staad together, say At 60s. Now. take your
stick OF thermometers out and turn il end
foremoS towards the sun or towards Il very /
}arge but distant fire; al The thermometers
may Essc, but they viii rise together, nc
difference belwecs the 'cae nearest the sun
and that fanbest from H. But now carry
ii near snali tire: thes@ne on the end near
est The fire viii rise say 90 75o; the middle
oae less, say to 200; the farther one stir
less, say TO $50. Thus, regarding the Ajs
DIE one as fired. both end ones have moreG
away from il in opposite directions by Tie
NC lion OF the sane fire; iust a. both water
surfaces moved away frOn the centre of the
earth by The same attractisn OF the mOoa.
Regreiting the iesgth OF this, and yot
doubling whether same points have beenl
given with sufficient fnkness, | rcaain
yours, very respectfully,
e. III. WINsT0r. !
Richmond College, Virginia, March q,
1881. i