, 1874-07-03

StnrtEIhg Dovo1Opmenta-ThoE Head OF
tho Comet to lso AS Nonr M Venua
over In to tho Enrtli-stronE. Probn-
biliay aiint tho Tail OF tho Comet WAL
Emtvrar tho EurtIl and the Moon.
70 tht Editor n Tie No,o York Tribune:
S1R: Permit mo again to congratulate Prof.
Swift upon tho rediaooyory Of what now prom
ihes to bo tho most wonderful and instructive
comot in the history Of tho world. Having u.s.
carlalned that tho nuclaus OF the comet WAS
moving in satisfactory accordance with tho orbit
which had computed, proceeded on tho 2Gth
inst. to compute tho position and probable ap-
paront magnitude, Of tho tail, in ordor, to learn
EeoG ana Goyop ~ woa a esa 1S G1s orn an1 20 70 s
bo visible ut all after tho head OF tho
comet disappears in tho woBt From my
own ehtimato Of Its length on tho morning Of
tho 25tl, after tho moon had aot, determined
100000 mics. I then assumed an increase OF
length OF one-tenth each day, and reached tho
startling result that upon July % its tail would
actually st,7ke our Garth. But knowing that II
orbit, it would fado away IN tho twilight without
making any unusual display, would not yen-
tnro to publish my results without further exam
inatlon. go
Win later observations Of creator accuracy, !
and am confirmed n tho opinion that wc shall
be either so noar tho fall OF tho comet, ~ it
H"eeps across tho eclipo. that i will fill largo
portion of tho hoavons or, ii its curvature il
within Il; and Tho phenomenon' msy be visible
Ia tho Nortlorn Hemisphoro, although'it is too
early yet to dotermina whether 1t may not DO
during the hours Of daylight In this coun.
try. At the rlek Of having erred in my judg-
tho nucleus and attendant conn Indicate tho
formation Of q tall equal to that Of Donatt's
comet which watched with 80 much cure, I
will venture some predictions, trusting that they
carly predictions Of tho future Of Donati'a
comet, and that they may bo as fully confirmed.
On Tuesday evening, juno 50, and on tho fol-
loving evening, tho moon will rise before tho
o9O O'clock, the comet Will bo oasily aoon by tho
nakcd oyo In tho northwestern sky (no other
description will be noaded), With tail about +
deg. In length. On succeeding evenings tile
ta win lncreaso In longth. so as to bring itesx.
tremity graiuaily. northward. On tho 14th Of
July the Ioad Of tho comet will have reached the
horizon In tho northwest as tho cad OF twilight,
50 that 1t will not ensily be- Visible aftor TINT
dato but tho tail will extend nearly to the polo
star -,
Donatis comet had q retrogrado motion, and
whom tho earth mot 1t, aud tho tail was most
brilliant. u was placed nearly at right angos with
ct, whose porihoon tliatanoe IL very little great
or, coming just within tho orbit Of Venus, ndyea
III the sRno direction with tho Garth, md nearly
with tho samo velocity (reduced to tho plane Of
tho equntor), In consequence Of which tho tail,
Of vision. will gradually turn toward us, still ap
parontly pointing nearly IN Tho samo direction.
It will DO remembered t!sat pouati'a aonlet wes
curved like l. soldiers plumo, but oogga's is now
curvature will be drootly from us, md therefore
inporceptiblo.. Another striking difference from
tho tails Of comets gencrally ia, TINT 1t will be 50
foreshortoncd ab to DO remarkably wide at Tho
end. 's
On July 1e, thu tail will extent. far beyond tho
OF rapidly toward the end. Within thfoo or four
daya after tho 18th, tho tail will hayo become 30
expanded in tile noighborhood Of tho polo an to
fill lnreo part of tho northern hoRvonH. Yct
It viii not DO conspicuous object. because il
will bo 30 faint % to look rhther like m Immense
cloud. or noN nlly-wnY, tllan what 1t really IL.
BY tlals time VIC ellall hare solved tho question
whether tho tail ia hollow, Or haa Fqdiatod
Of tho way in which this viii ontl, 1t Is not
aafo got TO- aponk with dctinitenosa; for al
though, ii tho tail woro straight. We shoull be
n1moat certainly noar the mlaalo Of 1t on July 2O
yet ita curvature will probably delay it two or
three dayg, aud even until tho eartl, las paused
heyornl its path. Taking tho bost vauo / can
from the records Of previous comets, / should
otxpeot tho oayth on jlly y 70 be wholly within
aesumo this to bo the caBc. Tho comet will then
1iHnppear to uH; but tlon tho Inhabitants OF aho
Southern Hemiaphoro, who may ba Ignorant Of
tho caugo Of tho luminosity Of tho eYoning sky,
will SEQ it gradually rise aud pass away, mud will
bB amazod by tile sudden appnration Of comet
OF extraordinary size md Hnal britliancy, which
will burst upon their vision az unforoaoen na the
grcnt comet of 1901. Tho gradunl din,lnutlon
nnd iinal disappearance Of tile oomct will bo 80
ncarly, tho conyorho Of wllat wo shall haye wit
noahcu hero TINT it needs 10 description.
What Will bo tho effect upon the earth 2 dare
not predict tho effoct upon tho ninta OF mon,
especially Of tho ignorant; but do not antiei-
pate any approclablo physical o1tout furtAor than
posBib!o electrical phenomena like tho aurora.
It will, OF courHo, loayo uH portion Of ita ut
uloHphore wl.on 1t dopnrtA, but, probably, not
/ enough TO affect the barometer, or to como
| within tho ougnt2ance Of scientists. But tl,era
/ may ho, by possibility, one pormauont otfoct OF
eoiontito Interest and curiosity. II tho oartl,
| should not ertlrc1y oBonpo, the moon will also
probably bo involved, al1d It will alao rotain q
portion OF tho coMotary substance. AH tho
amount Ct tho atmosphere upon tho moons s,ir-
fac0 ID now no amal, IT, Indeed, tAoro IL any at
AI that It a unrocognlza1le by tho nlcoBt astro-
lloM!cal SCRUTINY, perAapB after tho paHsage Of
the comet wo shall find TINT Ao,cotorth tho
| moon will 4ayo al Atmosphere, ii groator or
| loss density, which viii ,natoyla1ly modify tho
pAanomona Of ocoultatlonB aud solar oclipsos /
Will Rda that Venus Ia aufoly out of tia war, 80
tl,as tho transit expedition will NOT DO iutorfored
| with by tic gr0at comet Of 1874.
In Gfoud's Astronontica! Journal, Prof. Pierce
hnH doyolopoa means Of computing, with groas
accurpcy, from obseryod phonomcua, the form
| OF tho tall OF comet. 1intond, al soon as ]
nh6 y a