The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1859-01-22
Artronc mica Lecture by Professor o. M
Mitchell.
sup uoryoys ORBITS AND PHYSICAL CHAHACrEkiS-

yHE MOTIONS, ORBITS AM iH.s.oA~ S-~~
TICS OF COMETS
,.;,hs..rd,ny the severe storm OF rain last evening"
Aha Academy of Music filled with attentive audi
.pce Of ladies' and gentlemen to hearProf o. H. Mitchell
,.er his third lecture astronomy The subject spe
6cav discussed by the learned Professor was "The mo-
sous orbits and physical characteristics Of comets"
a coming forward the stage he was received with
tond appause by the audience The examinations, said
he which have been made thus far in regard to the pla
vets revolving around own central sun show those
bodes 10 be orderly their movements. We find them
rirenp about the sun with orbits which are nearly crcu
lar they are never sight through their entire
movements When the human eye is too weak TO follow
them the telescope TO its aid and gives us the ex
act position occupied by these worlds at all times We
know no clashing occur among them
We come TO night however, to very different class of
bodies moving in an irregular line, advancing from re-
xicps entirely unknown TO ussometmes with splendor
ht startes u.s. sometimes throwing out fiery banner for
,bousauds of miles, These bodies which We call comets,
h.ve Awakened the deepest interest in all ages of the
world Even now when science fills the world, no new
one appear in the heavens without causing us 70
feel may perhaps take such direction as 70 Involve
the world in destruction No science can anticipate or
yrase known the of these nery bodies We can
rot anticipate their returns or predict their movements
There doubtless an nnumerable number OF them CIR
natipr around the which have never appeared to
he eve OF man Permit me to direct your attention TO
he data which requisite TO determine the movements
II these wandering bodies In our solar system every
body which belongs is linked 10 every other body
Ard in considering their relation 10 COMETS let
us first refer to their weight. What Is the
quantity of matter contained IN the sun itself
How shall weigh this ponderoas central orb What
mighty scale shall be invented by human genius TO
weigh this mighty world and give to us its exact quan
gyY This be done before can compute the periods
of comets Then must weigh every planet belonging
80 our stem every satellite belonging thereto, anc
also determine the distance of every planet from tee
sun We must find the amount Of force that proPels
the planets in their orbits. We must go from planet to
planet and get this data before we can resolve tins pro-
blem of the comets Now we weigh the sun
he
earths-sod orbs like our own-placea IN one
W. oSer scale The amount of matter contained in any
world is this way Take any body and drop
let heavy body be dropped the earth, and 1t falls
s hodv At Venus and IL falls the same space in the
same tme Venus is as large or as heavy the earth
its velocity is only half as great then venus Us ony
half large the earth Well, We cannot go 70 the
papes and make this experiment; must determine the
weights planets another way The earth was propelled
INTO space right line but seized by the attraction OF
the sum- il broke away from the right line and moves in
circle So the propelled into space in right line,
rs diverged circular pathway by the attraction Of the
earth Let that the earth attracts the moon
with the same power the attracts the earth,
or that the influence Of the sun upon the eartn
is equal TO the influence OF the earth upon
the moon. Then the sun, it must be remem-
bered, is at a far greater distance from the
earth than the earth is from the moon. Know
ing the OF the earth and the greater distance or
the sun be calculated how much greater the size
of the the earth requires 1854 e36 orbs Of the
size OF the earth TO be large weigh as much as the
gun. The planets have all been weighed the quantity OF
matter which they contain has been ascetaned far as
the instruments in can decide It, The ancients thought
that the comets generated in our own atmosphere
though Of them to have had more correct de
and 10 have prophesied that the time would come when
their orbits aud periods would be known. Can the
mighty power Of attraction which guides the planets ex
tend itself over the comets? Assuredy does. Is il posi-
bic 20 determine the figure Of comets orbits
the distance they sweep through space and point
for ali time 10 come their movements? Newton examined
The orbit Of the great OF 1880 and found that it
would return in 5i5 years, and that swept out into
IF of, no That
very Ike IT, had appeared from the earliest annals at
periods Of about o'5 years apart the exact
predicted, because they subject TO disturbing
causes, and do not always complete their orbits
in exactly the time Shortly after the celebrated
astronomer Edward Haley arose. and by his science an
skill added much to our knowledge of the orbits Of comets
Aer rigorous examination OF the comet which he behed
when returning from St Helena, he found 70 his great
delight that IL mad an orbit of very limited period
namely, seventy five years. He then turned 10 history
aud found that comet answering TO It's description, had
at stated intervals Of about seventy five years
apart He found that the elements Of those supposed
different comets were very nearly similar He announced
world that at the end OF seventy five years tim,
the inhabitants that tnen lived should behold tne return
OF that blazing wanderer and, true 70 his prediction,
thus returned. With great pathos he told them to re
member that the prophecy Of the comets return was hrs
told by an En.hman Seventeen years after his dealt
the comet appeared All the science of the world was
employed just before its appearance to tell in what par
81 tie heavens and at what exact time II would appear
Three Distinguished geometrieans finally solved the pro
HEM and announced that the 17n of April, 1889, thu
TOO much for the exact date of the of
cennot be predicted because Of disturbing causes
hut il did apge December OF that year. To oreel 81
nearly the period Of that fery wanderers return from
distant space coming back true to the law of attraction
was DO small triumph for science. But they did no
that Jupiter had delayed il 10 its return us day
aad Saturn l00 days Thirty days the ouly il
seventy years and the would not have been
rrea, had Jupiter weight been known well then
Then that error would have shrunk into nneteei
days
all that have appeared since the telescope ha
been directed towards the heavens wnat are the OBJ
IN nlfa mo nThff Cnr1qf
Is possible by looking at of these bodies in the hen
you tell anything about ir If the telescope
directed at comet to night, and Us place fixed exactly
with reference TO fixed star you have obseva
zion; "a IS hours Afterwards note the exact posi-
ton Of the comet with relation TO some xed STAR and tn
exact tu is there 70 second. Three such observa
tons sufficient to determine everything about tn
orbit and velocity Of the comet How that is Sufficient
tel you cannot here enter into explanation
the calculation. You will have to take the statement 81
credit
VIII low refer to the physical consultation Of the.
bodes they entirely different from the physcal
of the other heavenly bodies far know
le.ge of them extends Their aspects always chang
ing; planets aEa& appear the same with well deanet
dsk ou, comets iser nave a wen defined disk, y
apowerfa telescope u is true that some Of the comets
they the face OF the sum- appear dark
black, but is not therefore, certain that they solid
We know that most Of the comets nebulous and thai
the of matter that they contain is exceedingly
small. There has never yet comet passed through
system containing sufficient TO affect in the leas
the periods orbits o. any Of the planets satellites
Comets nave passed right among tae satellites Of Jupiter
but they did not affect them in the least The decacy
the equilibrium Of the rings of Saturn very great IN
slightest interference OF influence would have siecte
their movements and position. Those rings have del
cacy that might be called equilibrium Of instability
We know that for hundreds and thousands Of the
have been sweeping through space, their equi brium d
in the least destroyed affected. any comet had
fcted our system it would have destroyed the elul
brum OF those rings
What the Of those vast trails Of light which
call tails thrown of INTO spacey Here acknowledge
amystery know not how 10 solve this mystery. Thes
trails Of light have been examined with all the th
Is possible, but cannot explain Their phenomena I'll
great comet OF 1850 threw out tail 100 900 Of mile
So length. Waat comprises ~ what directs tY This ira
Of light thrown on with velocity almost beyond con
prehenson; hfoows the comet toward the but wbe
the comets or into space tese trains of light pre-
oede them. What IS il that throws OF these trains
lighty You may ask II gray iation does accour
for il. answer no. think grayittton cannot accout
Tor any 81 10. How could gravtaton exert a power
drive material matter in direction directly opposite
the attraction itsefY We mus; look 10 the comets then
solves for some power 10 throw out drive G
these trains OF light. You all watched the com
which recently approached system vii
great interest. II for tho IA