John Winthrop.

Two lectures on comets online

. (page 12 of 14)
Online LibraryJohn WinthropTwo lectures on comets → online text (page 12 of 14)
Font size
QR-code for this ebook


great beyond human conception ; consequently they
"Were at liberty to share amongst themselves, without
any molestation from the planets, all that part of the
fluid, which filled the vast spaces of the system, with-
out the planetary regions ; therefore if the hypothesis
be granted, they must necessarily have such atmos-
pheres, as, in fact, we find they have, and which, in
their descent through the planetary spheres, are, by
the (supposed) repulsion of the sun's atmosphere,
driven to such astonishing distances behind them, as
occasion me-y require. Ihose whose aphelion dis*
tances v.'ere greatest, being more solitary, would con*
dense round them the greatest atmospheres, and such,
their greater distance's from th.e sun would require,
upon the fcregoing principles, to make them com-
fortable habitLitions. As the lengths of their tails
14



158 AFPENJJIX.

would probably, at equal distances from the sun, be
proportional to the quantities of this repellent matter
contained in their atmospheres respectively, it may
not be impossible to form a rational conjecture of their
real aphelion distances, by observing the apparent
lengths of their tails, when at equal distances from
the sun, in their descent, and thence computing their
real lengths, and comparing those whose aphelion
distances are unknown with those which are alre:-.dy
determined ; and as nearly as we can by this method
Gome at their greatest distances from the sun, so
nearly may we (by comparing their computed tra-
jectories, with those distances,) determine their mean
distances and periodic revolutions. But this is hum-
bly submitted to better judges, and is designed only
as a hint for future inquiries.



/;... 6



IW L

-Q — e — I — \ — 1 — 'A — \ — ^-



A



Fio I



V









T



B






A^^^



Fio. I




4^=-



"s -^St-



SUPPLEMENT,

CONTAINING AN ACCOUNT OF THE COMET OF ^ "^
INCIDENTAL REMAKES.

JL HE Comet which we have had the grat.iACLf;on of
beholding, more than thiee months, 4ad^v:iich is still
faintly visible, [Dec 20] has been more biillianl and
striking than any which has been seen since 1769. In
Boston, it was first noticed on the 4th of September
by a gentleman riding into town in the evening. It
had been seen, some days previously, at Portland, in
the morning, by two gentlemen who rose, at an earlv
horn', to take seats in a stage. Its first appearance
was faint and nebulous. On the 6th of September it was
very conspicuous, and was ascertained to be a Comet.
Professor Farrar's first observation was made on that
evening, at Cambridge. It was then under the square
of Ursa Major. This Comet was seen at Vivieres in
France, on the 25th March last, by M. Flaugergues;
at Marseilles on the 11th of April by M. Pons ; and
at Paris on the 20th of May. It continued visible
there, till the end of May ; audit has been announced,
in some of our public papers, that a Comet was ob-
served in May, at Chilicoihe.



■160 s;l?PPLEMENT.

M. O'ibers, of Bremen, in a letter to Professor Bo-
den, which bus been published, announced that it
would re-appear before the end of August, that it
would be much more visible than in the spring-, that
its greatest brilliancy would be in October, and that
it would still be visible in December. Tliis has all
been veriBed. It w^as seen again, both in France and
in England, on the 21st of August. It then ''had
" the appearance" says Cujicl Lfft^ " of a large Ne-
'*■ bula. Fxcarly circular, and of about one degree in dia -
" meter, with a central light, like that of Andromeda,
^'- resembling a hazy star of the fourth or fifth mag-
<^ nitude. Right ascension, 149° or 150". North de-
" clination, nearly 36°.'* On the 6th of September,
it was considerably brighter, and M. Lofft observes,
that its train then, viewed with good glasses, was
" evidently divided by a darkish shade near the far-
" thest extremity.'' On the seventh of September,
he describes its train as about 6 degrees in length :
the breadth of the head, including the diffused Coma,
about \ or 4 of the moon's apparent diameter. Ob-
servations on this Comet, have been made, in differ-
ent parts of the United States, with laudable attention,
and have been occasionally published in the news-
papers. The elements of its orbit were given by
Nathaniel Rowditch, Esq. of Salem, in the following
communication, published October 11, in the Salem
Gazette.

" The geocentric longitudes and latitudes of the
Comet, used in fmding the elements of the orbit,



SUPPLEMENT. 161

were deduced from distances of the Comet from jiix-
turusi Lyj-a, and Diibhe^ observed at Cambridge by
Professor Farrar, and at Nantucket by the Hon. Wal-
ter Folger, jun. By combining the observations of
September 6, 9, 12, 15, 18, and 23, the elements of
the orbit were found by the method of La Place, and
corrected by the observations of September 6, 15 and
23.

^'Perihelion distance, 1.052. The mean distance of
the earth from the sun being 1.

"Timeof passing the perihelion September 6, 1811,
at 18h. Greenwich time.

" Place of the perihelion counted on the orbit of the
Comet, 2s. 2 Id.

" Longitude of the ascending node, 4s. 1 8d.

" Inclinalion of the orbit to the ecliptic, 74d,

" Motion retrograde.

" These elements will require "some corrections,
(perhaps two or three degrees) to be determined when
a greater number of observations, on a longer arch of
the orbit, shall be made. The observations made
early in September were Tuible to a small error, from
the uncertainty of the refraction, the Comet having
been observed near to the horizon.

"These elements differ from those of all the Comets
whose orbits have been calculated ; as may be seen
by examining the tables of La Lande and Vince, or
that in Rees's Cyclopedia under the article ' Comet.*
This Comet is therefore one that has been before un-
known to astronomers.



162



SUPPLEME^it,



*■ Wishing to estimate nearly the apparent course of
the Comet from these elements, I described a circle
on a stiff piece of paper to represent the orbit of the
earth, and a parabola corresponding to it, for the or-
bit of the Comet (similar to fig. 267. vol. 3. edit. 3.
of La Lande's Astronomy) and marked on these
curves the places of those bodies for each day of the
present year. A slit being cut through the circle in
the direction of the line of nodes, the parabola was in-
serted so as to be inclined to the ecliptic by an angle
of 74*^, the point representing the perihelion being
above the plane of the ecliptic, so as to make the
angle at the sun by the perihelion and node 57^. By
this apparatus, the following estimate of the appa-
rent course of the Comet and its distance from the
earth were made.

"In the month of February 1811, the Comet was
near to the eastern part of the constellation Argo. Its
motion was then west, inclining to the north. It pas-
sed a few degrees to the eastward of tlse Great Dog,
and its direction then became nearly north, being sta-
tionary in longitude in the month of May. It passed
near to the eastern part of the Lesser Dog, early in
June, inclining rather towards the east. On the 16ih.
of July it passed the ascending node in the longitude
of about 4 signs S degrees, and then moved northeast-
erly towards the feet of the Great Bear, where it
was first seen, after tl)c conjunction with the sun, on
the sixth of September. On the 5th of October it
was near the right hand of Bootes. It wil! be at its



SUPPLEMENT. 163

a'reatest north latitude about the middle of October,
near the right foot of Hercules, after whicii it will be-
gin to move towards the ecliptic, through the left knee
of Hercules, towards the Ecigle,the Dolphin, the Wa-
ter-Bearer, he. It will be near tlie Eagle about the
first of December. It is to be observed that the appa,-
pent positions thus roughly estimated, are liable to an
error of two or three degrees. The orbit of the
Comet falls without the earth's orbit.

" The distances of the Comet from the earth, ex-
pressed, Jn pans of the sun's distance from the earth,
estimated as 10, were found in February 1811, to be
30 ; in June, when visible at the Cape of Good Hope
and at other places south of the equator, 23 ; on the
6th of September, 17. About the middle of this month
(October) it will be at its least distance, 13; after
which it will increase, and in the month of Decem-
ber it will be about as far distant as in June. In the
latter part of January, and in February, 1812, the dis-
tance will be above 30 ; the latitude of the Comet
will then be small ; and as it will be nearly in con-
junction v/ith the sun, it will probably then be invisi-
ble. The least distance of the Comet from the earth
is about 120 millions of miles. The least distance of
the Comet from the sun, 100 millions of miles.

'^ The tail of the Comet has been observed to be 10
or 12 degrees in length, which would make its real
length nearly equal to half the dieitance of the earth
from the suii."



164 SU IMPLEMENT,

On the 1st of November, the following additional ol?-
servaiions were inserted, by Mr.Bowditch, in the same
paper.

" In the account of the Comet published in the Ga-
zettee of the lltii uit it was observed that each of
the elements might require a correction of two or
three degrees, on account of the shortness of the
arch described in the mterval between the observa-
tions used in those calculations. To determine nearly
those corrections, the observuiioi.s of September 6
and 30, and October 21, were combined, which fur-
nished the following corrected elements:

" Perihelion distance 1,032, the mean distance of
the sun from the earth being 1.

<' Time of passing the perihelion September 12th, 3h.
1811, Greenwich time.

*' Place of the perihelion, counted on the orbit of
the Comet, 2s. 15d. 14m.

"Longitude of the ascending node, 4s. 20d. 24m.

"Inclination of the orbit to the ecliptic, 73d. Om.

" Motion retrograde.

" These elements give the geocentric longitudes
and lattitudes of the Comet from September 6 to Oc-
tober 21, very nearly as they were observed. It may
however be necessary to apply some small corrections,
to be determined by repeating the calculation with a
greater number of observations.

" These small variations in the elements do not pro-
duce any great change in the apparent path, and in
the distances of the Comet from the earth given in
the ff;rmer paper.'*



SUPPLEMENT. 16d

The well known accuracy of Mr. Bowditch, in cal-
culations of this sort, induced a reliance on the cor-
rectness of these results, with the qualitications ex-
pressed ; and the public felt indebted to that gentle-
man for his early attention to the subject.

Mr. Bowditch's calculations of the Comet of 1807,
were published in about six weeks after its first ap-
pearance. They may be seen in the Memoirs of the
American Academy of Arts and Sciences, vol. iii.-
part 1.

In the Journal De Physique, for August 1808, the
elements of the same Comet are given by an Euro-
pean astronomer, Mr. Bessel, adjunct with Schroeter,
at the observatory near Bremen. The coincidence is
striking, and in every view gratifying, as it fixes our
confidence in calculations of this description. The
differences between the two calculations, is only thus:
In the time of passing the perihelion 2 hours 27' oA>^
In the longitude of the ascending node, 21'
In the place of the perihelion, i'

In the inclination of the orbit, 5'y*

In the perihelion distance, ,00314

. We fortunately have it in our power to compare
Mr. Bowditch's calculations, of the present Comet,
with those of another eminent calculator, in France,
M. Burckhardt. The elements of this Comet, a.s
published by him in Paris on the 20th September, are
as follow :

Perihelion distance, 1.0224



166 SUPPLEMENT.

Moment of passing the perihelion, Sep-
tember 12, 9 o'clock p. M. 48m.

Ascending node, 140° 13' or 4s. 20d 13m.

Inclination, 72° 48m.

Picxe of perihelion, 74« 12 or 2s. 14d. 12m.

The differences, it will be perceived, between the
American and French results are very trifling, and
leave no doubt of their near approximation to the
truth. Speaking of the perihelion, M. JBurckhardt
adds " since that time, the distance of the Comet
from the sun has increased, but the distance fi (.m
the earth will continue to diminish till towards the
middle of October. Then, the least distance from the
earth to the Comet will be upwards of 41 mi/iions of
leagues."

Mr. Bowditch's results have thus obtained most re-
spectable support, and are fully vindicated, if vindica-
tion were necessary, from the animadversions made
by Mr. John Wood, in the Richmond Inquirer. That
gentleman contends, that the Comet had not come to
its perihelion on the 1st of Octoberc To these re-
marks, Mr. Bowditch gave a brief, but satisfactory
reply in the Salem Gazette of November 15. Mr.
Wood's strictures are more exceptionable, as they
were hazarded without any calculations, from the
numerous observations which he had made with com-
mendable industry, and probably with correctness.
His conclusions are founded on appearances, in their
nature equivocal, and which were capable of a ready
sijlution, in perfect consistency with the results of M'.-.



SUPPLEMENT. 167

Bov/ditch's investigations. Mr. Wood, for instance,
contends, that the motion of the Comet was direct
2ii\Ci i\Q\. retrograde^ as stated by Mr. Bowditch ; and
that the inclination, instead of being 74 degrees, can-
not exceed 64 degrees. This remark is at once an-
swered by Mr. Bowditch, by observing, that he gives
the proper motion and angle of inclination, in refer-
ence to the sun, according to uniform practice. Mr.
Wood has reference to a view from the earth. It
may be here observed, that the same Comet during
its appearance, may be direct and retrograde at dif-
ferent times, as seen from the earth. The apparent
motion of the present Comet, in February and March
18 J I, was retrograde, but it is now direct. Mr. Wood
has observed that the method of La Place, and ail other
methods, leave great uncertainty in the results. " I
^m confident,*' says Mr. Bowditch," that this assertion
would not have been made, had he been acquainted
with that elegant method of calculation." And as to
the opinion expressed by Mr. Wood, that till a greater
number of observations should be obtained, any cal-
culations of the elements must be extremely errone-
ous, Mr. Bowditch observes, " In this Mr. Wood is
much mistaken. The Comet has now been visible
above two months ; and it is not unusual in Europe to
have the elements of the orbit of a Comet, to a con-
siderable degree of accuracy, in a week or ten days
after its first appearance."

In the London Courier of October 9, we find the
elements of this con^et given by Andrew Ure, from



168 SUPPLEMENT.

observations made at the Glasgow Observatory. The
calculations are from five observaiions, made on the
1st, 8th, 15th, 23d, and 30th of September, the for-
mula of La Place were pursued, and Mr. Ure was
assisted by Mr. Cross, his mathematical associate in
the Andersonian Institution. These gentlemen give,
as the result of their calculations, the peiihelion dis-
tance 94,724,260 miles.

Time of the perihelion, September 9.

Comet's distance from the earth, September 15^
. 142,500,000 miles.

Comet's distance from the sun on the same day,
95,258,840 miles.

Distance of the earth from the sun, at that time,
^^505,9 32 miles.

Length of the tail 33,000,000 of miles.

Motion of the comet retrograde.

According to this calculation the perihelion dis-
tance was about 170,000 miles nearer to the sun, than
the mean distance of the earth from that luminary.
There is a difference of three days in time from that
given by Messrs. Burckhardt and Bowditch. The
pluce of perihelion, longitude of the ascending node,
and inclination of the comet's orbit, are not given.

Mr. Ure, having afterward seen M. Burckhardt's
account, thought it necessary to add some explana-
tory remarks. " The talents of M. Burckhardt as a
computer," he observes, " are well known, and highly
appreciated by the learned world;" but he still ex-
presses a confidence in the elements he had comn'.Ur-



SUPPLEMENT. 169

mcated. " The time of the perihelion passage,"
he says, " may be pretty accurately fixed either for
Sepiember 12, or 9, or, as is more probable, at some
intermediate period."

It was g-ratifying to find the elements of this comet
presented to the committee of the overseers of the
University in Cambridge, at an -exhibition on the 2 2d
of October, calculated by one of the students of the
senior class, and accompanied with a neat graphical
representation. The following were the results as
given in that young gentleman's performance.

1. Perihelion distance 1.1, the earth*s mean dis-
tance being 1.

2. Time of passing the perihelion, September 6. •

3. Place of perihelion, 2s. 22^.

4. Place of ascending node, 4s. 15.

5. Inclination, 77*'.

6. Motion retrograde.

7. Passed the ascending node July 27.

8. Distance from the earth's path when on the node,
34,600,000 miles.

Diameter of the comet, including the coma imme-
diately surrounding it, 132,200 miles. The appctrent
diameter, as measured by a micrometer, being 2' 46''.

Diameter of the nucleus, estimated at about half
the diameter of the earth. Its apparent diameter could
not be measured by the micrometer, the nucleus be-
ing too indistinct.

The length of th e tail, 70,000,000 miles; the angle
Ainder which it was seen, October 19, being U^^ 30'.
15



i7# SUPPLEMENT.

These results have been obligingly communicated
by Professor Farrar, upon request. He observes that
they were obtained by the graphical method, " six
" geocentric latitudes and longitudes being employed,
« viz. those for the 6th, 14th, 20th, 24th, and 30th of
" September, and 17th of October. A paper was
<' stretched upon a plain board, to represent the eclip-
"^.tic, on which was drawn the path of the earth, and
" its place for the above times : From these several
<' points were set off the elongations of the comet,
" and threads raised to represent the latitude. This
*' being done, different parabolas, divided into days,
" were applied, the focus being kept in the sun, until
" one was found which gave, nearly, the observed
*' places of the comet."

" Great accuracy," he adds, " is npt to be expected
** from this method, particularly in the time of pass-
im ing the perihelion, when no very considerable ine-
" quality in the motion of the comet takes place, dur-
" ing the several intervals between the observations.**

To Professor Farrar we are indebted also for the
following communication.

" From September 6, to December 10, the comet
" described an arc of about 121°, as seen from the
<' earth. When it first appeared, it moved at the rate
"of about 1° per day. Its velocity increased till it
" amounted to a little more than l^° per day, and
" then began to decrease till about the middle of No-
" vember, when it returned to its former rate of I*' ;
" and now, lOth December, it is about three fourth?



SU1»PLEMENT. 171

"•^ of a degree. It came within the circle of perpetual
" apparition, about the 20th of September, and con-
" tinued about 20 days. It reached its greatest nor-
" thern declination, 50°, near the 2d of October, and
" its greatest northern latitude, 63|-*, about the 17th.
" At this time also its motion in longitude was at its
" maximum On the 6th of September, when it was
" first seen, it was about 18*, west of the sun in
" longitude. After continuing for some time at about
<' the same distance, it gained upon the sun, and about
" the 1 1th it came up with it, and passing it, arrived
" at its greatest elongation, 53', about the 10th No-
" vember. From this time it has been continually
" falling back, with respect to the sun. It loses now
" at the rate of more than half a degree per day ; and
" this quantity is increasing, and of course must soon
" reduce its present direct distance, 46**, within the
" compass of the twilight, when the comet will dis-
" appear, again to come into conjunction with the sun.
" After which the sun will move on to the east of the
" comet, leaving the comet behind, to pass off into
" the southern hemisphere. The comet will now rise
" in the morning before the sun ; and, when it gets
" out of the twilight, may perhaps be seen again by the
" help of the best glasses. Its present distance, from
'' the earth, is about double what it was when in pe-
" rigee."

M. Burckhardt, in his communication above men-
tioned, makes the following interesting remarks.
" The nucleus of this comet appears separated from



172 SUPPLEMENT.

" its coma^ which surrounds it in the form of a para-
" bolic ring. This appearance, which has not yet
" been observed in other comets, is ascertained by
" the observations of all the astronomers of Paris,
*' and will doubtless be confirmed by those of other
" astronomers. Probably, however, it does not at all
'• follow, that the body is absolutely detached from the
'' coma , as the space, which appears void, may be filled
" with particles much less luminous than the rest of
" the coma."^

The description given by M. Burckhardt is con-
firmed by Professor Farrar's observations, as will ap-
pear by an extract from his minutes. " September
*' 18, observed a kind of dark ground, round the head,
" for the space of four or five times its diameter, and
^^ then a luminous appearance, somewhat resembling
*' a halo, on the side opposite to the tail, very appa-
*' rent, even through an achromatic refractor. It
*' struck me as a peculiarity, and I called several per-
*' sons to look at the comet, and to describe to me its
" appearance. They made the same observation ; and
" one compared the form of this light to that of a cur-
" rent of water, flowing round a stick, or other obsta-
" cle. A slight sketch was copied upon paper ; but,
" upon looking into Hevelius, I found that some of the
" representations, which he had drawn from mere
*' verbal descriptions, agreed so far with what I had
" remarked in this comet, that I ceased to regard it
<' as altogether new."

The Rev. Dr. Piincc, of Salem, who made repeat-
ed observations on the comet with an excellent night



SUPPLEMENT. 173

gksSj makes the following remarks in a letter to a
friend. " I saw it more distinctly about the middle
" of October, than at any other time. The tail was
" very much forked, the light being very strong on
" the two sides of the tail, and very faint towards the
" middle. In some part, included between the head
" and two points of the tail, the space appeared as
" dark as on the outside of the comet, or the unillu-
" minated part of the heavens. The forks were taper-
" ing to a point. I could discern a little more light in
" the space about the axis of the cone, which formed
** the tail, when I moved the glass, than when it was
" at rest, but the light was gradually diminished from
" the two inner sides of the forked tail, till it wholly
" disappeared, near the axis toward the end. This is
" what is called a bifurcated comet, and appears in
" my night-glass more pointed or angular than when
" seen with the naked eye. Its appearance is different
" from the comet seen here in 1807, the tail of which
" spread with a uniform light."

La Lande's table comprehends 78 comets, the ele-
ments of whose orbits have been ascertained. It
ends January 1790. In the Journal De Physique for
August 1808, a supplementary table is given, pre-
senting the elements of 19 more, all subsequent to
January 7, 1790, and many of them calculated by the
celebrated Olbers. This table ends with the comet
of 1807, which, of course, combining the numbers of
the two tables, is the 97th comet, and the comet of
1811 is the 98th.
*15



174 StJPPLEMENT.

The table inserted in Dr. Rees' New Cyclopsedia
(American edition) includes three comets not con-
tained in La Lande's table. One of 539, A. C. one
of 1097, AD and one of 1351. Of the last the ele-
ments are only partially given. In De La Lande's
tables, also, the comet of 1532, and 1661, are consi-
dered as one ; and that of 1556, the same as that of
1264. This makes a difference oi Jive^ between the
two tables, in their enumeration. Dr. Rees* num-
bers are more conformable to the opinion expressed
by La Place, and other, astronomers of eminence, that
the return of but one comet is ascertained — that of
17'59, which corresponds with the elements of three
preceding appearances, at intervening periods very


1 2 3 4 5 6 7 8 9 10 12 14

Online LibraryJohn WinthropTwo lectures on comets → online text (page 12 of 14)