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in he asserts, that " The form of the electrical atmosphere is
'* that of the body it surrounds." — ^This he proves by experi-
meJits, and from this principle has g'iven a probrible solution
of the operation of points, at a dlstaace from t!ie electrified
bodies.

10



110 ON COMETS.

may infer the repellency of its constituent particles
themselves.

This property is also largely treated of by Doctor
Franklin^* and is as necessary to most electrical ex-
periments, as the former is to ail ; and, doubtless, con-
tributes one half to the amazing rapidity of lightning,
to which nothing, short of that of the rays of light,
can be compared.

Profi. 3. When two small spherical bodies have
electrical atmospheres, condensed round them ; those
atmospheres are mutually repellent : As we have en-
deavoured to prove, from the known mutual repellen-
cy of the particles of air, that the atmospheres of the
heavenly bodies are, amongst themselves.

This proposition naturally results from the last, and
is, in some measure, involved in it ; but, as the expe-
riments now to be produced in support of it, may
shew us in what manner the electric atmospheres act
upon, and affect each other, it deserves a more parti-
cular consideration. For, as these atmospheres are

* See Franklin's letters, p. 37. § 5. where he says, " Every
** particle of matter electrified, is repelled by every other par-
«' tide, equally electrified. Thus the stream of a fountain,
*» naturally dense and continual, when electrified, will separate
«' and spread In the form of a brush, every drop endeavouring
« to recede from every other di-op. But on taking out the elec-
** trical fire, they close again." To which may be added, that,
if a small tin cup, filled with water, having a spout just big
enough to let out the water by distinct drops, be electrified, the
water will issue from the mouth of the spout in a diverging
mist, so long as the cup remains charged, but as soon as dis-
charged again, will fall in distinct drops as before.



ON COMETS. Ill

invisible, in themselves, and are discoverable, only by
their effects, it is necessary to charge them with some
substances vv^hich reflect the rays of light, in order to
render them proper subjects of observation. — But the
dust, powders, &c. used in the preceding experiment
will not answer that purpose, as they fly off, mstantly,
upon their receiving, and condensing round them^'
selves a certain portion of the fluid : Instead of which,
if fine limber threads are run through the balls, in
various directions, and their ends cut off at equal
lengths, these threads, as they cannot escape, shew,
by their several directions, the tendencies of the elec-
tric atmospheres of the bodies they adhere to.

This being premised, we proceed to the following

EXPERIMENT II.

Let a pellet of cork or pith, thus prepared, be sus-
pended, and electrified; the threads will diverge,
equally, every way, from its centre as at A Fig. 6.
the electric atmosphere being equally condensed, up-
on overy part of it, and equirepellent from its centre
outward. But if two such balls be suspended and
electrified, and caused to approach each other, the
threads of each, which happen to be next to the other,
instead of standing out every way from the centre, as
before, will be incurvated towards the line of opposi-
tion, as at B andC ; whereby the reciprocal repulsion
of their atmospheres is rendered visible, as the direc-
tions of the threads shew the tendencies of those at-
mospheres respectively -, from which it appears, that



112* ON COMETS.

they recede from each other, as far as the mutual at-
traction subsisting between each atmosphere and its
own ball, (which at first occasioned a condensation of
the former round the latter,) will permit. But that
the atmospheres do not wholly fly off, in consequence
of this repulsion, is evident, as the threads continue
in the same directions, until one, or both be discharged.

Quere, Does not this experiment abundantly con-
firm and illustrate the reasoning in page ^5^ relative
to the passage of two planets, or comets, attended
with large serial atmospheres, by each other ; whose
mutual effects are represented at C and D, Fig. 3 ?

We shall adduce one experiment more, before we.
close this subject, which may prove as entertaining
to him who will be at the trouble of making it, as it is
demonstrative of the principle under consideration.

EXPERIMENT III.

Provide a wooden sphere, of four or five inches in
diameter (call it A ;) let it be gilt, as the metal will
better condense the electric fluid upon its surface ;
also a small pellet, of cork, or pith of elder (which
call B,) strung, as in the last experiment, with a few
threads, of three or four inches in length : Suppose
A to represent the sun, B, a comet; fix. A on the
wire of an electric bottle, and suspend B by a silken
thread from a point, directly over the centre of A, so
as that, when neither of them is electrified, B may
rest against A, a little bflow the level of its centre ;
and charge both ball and pellet. The mutual repel-



ON COMETS. 113

lency of their electric atmospheres is so great, as that
that of B is thrown off as far from A, as the mutual
attraction between the pellet and its atmosphere will
permit ; which attraction is at the same time so
strong, as that, rather than suffer a separation, the
pellet flies off" with its atmosphere, to a certain dis-
tance from A, where its natural gravitation to the
earth is just balanced by the repellent force of the
two atmospheres : There B remains at rest, while its
atmosphere retires as much farther as possible from
A, without quitting it wholly ; instead of which it un-
dergoes a longitudinal dilatation, in opposition to the
centre of A, as the atmospheres of comets do, with
regard to the sun : This is evident from the direc-
tions of the threads, which, observed in a side view,
bear a near resemblance to the tails of comets. When
the pellet is in this situation, blow it gently with a
bellows, in a direction perpendicular to the line con-
necting the centres ; this will give it a projectile mo-
tion, which will be regulated by its common gravita-
tion ; and as the centre of A is directly under the
point from which B is suspended, the latter will be
carried round the former, as the centre of its motion.
Thus will this little comet perform many revolutions
round its electric sun, and in every one, and through
every part of each, the tail of threads will constantly
maintain its opposition to it, as the tails of comets do
to the sun in the heavens.

This experiment was very agreeably repeated with
an artificial comet, consisting of a small, gilt cork
ball, with a tail of leaf-gold, about two inches and an
*10



'114



ON COMETS.



half in length ; when, during the whole time of the
experiment, in which it performed, at least, twenty-
revolutions, the tail, as nearly as the eye could judge,
was constantly projected in the line of the opposition
of the centres of the two balls ; the thread, by which
the smaller one was suspended, either twisting, or un-
twisting, the same way, during the whole time. When
thus in motion, if we raised the globe, the tail was
depressed ; when it was lowered, the tail was ele-
vated ; maintaining its opposition, in every situation.

But now, from these experiments, some may, per-
haps, be inclined to think, that the electric fluid is
the sole cause of the phaenomena of the tails of Com-
,ets : That the sun, as it is the grand source of light
and heat, throughout our system, may be the fountain,
from which this element, also, is somehow derived to
its several globes : That Comets, for wise ends, un-
known to us, have a larger share of this fluid than the
planets ; and that, when they approach the sun's elec-
trical atmosphere, their own are thereby repelled, as
in the foregoing experiments ; and appear as lucid,
diverging beams, like those which, in the dark, we
see streaming from electrified points.

This hypothesis might indeed solve the phasnomena
of the cometic tails, provided the electric atmospheres
of bodies, charged with that fluid, were visible in any
of our experiments, even when made in the dark :
But as that is never the case, unless the fluid be in
motion ; and as the proof of the existence of such at-
inos'Dheres, when at rest, depends solely upon their
effects upon other substances, the hypothesis cannot



ON COMETS. 115

be admitted. Were this indeed the true and sole
cause of the phaeiiomena, a planet, near which a Comet
might happen to pass, would be in a situation, truly
hazardous ; for it is evident that the planets (upon
that supposition) are not accommodated with such
vast electric atmospheres as attend the Comets ; con-
sequently, have not the same proportion of that fluid
condensed round them, but far short of it: — There-
fore, whenever the electric tail of a Comet passed
near a planet, it would be attracted by z7, be drawn
aside, from its opposition to the sun, towards zV, and
upon it discharge the mirfilussage of its fire, that both
might have equal, or proportional shares ; which dis-
charge, if we consider the snap of a small spark be-
tween two cork pellets, and enlarge the idea, propor-
tionably, to that instantaneous cataract of fire which
would necessarily take place between two worlds in
similar situations, we may well imagine would give
an explosion, which nothing could equal, short of the
final voice of an archangel ; and, if it were not suffi-
cient to rouse the ashes of the dead, might reduce
the living to their primitive dust. But such a catas-
trophe, we have not the least reason to dread, from
the neighbourhood of a Comet, unless we can sup-
pose, that infinite wisdom and goodness would create
one world, merely for the destruction of another;
as we cannot conceive of any other ends, to which
such huge electrical atmospheres could he adapted.
Indeed the discharge would be equally fatal to both
worlds ; as it is certain from electrical experiments,
that the effecis of a stroke of lightning are the same,



116 ON COMETS.

ivhether the flash proceeds from the cloud to the
earth, or is descharged from the earth mto the cloud,
both of which have happened during the same thun-
der-gust ; as appears from observations made by Mr.
Kinnttrsly and Doctor Franklin^* communicated to
the Royal Society. But to put this matter beyond all
reasonable doubt, we may further observe, that if the
phsenomena of Comet's tails arose from the same
cause, which renders the electric stream visible,
when proceeding from a steel point, these tails would
shine by their own light, as the electric fluid does,
when in motion ; whereas, an apparent obscuration or
defect, in one of those tails, has been observed, which
evidently arose from the shadow of its nucleus, which
occasioned a partial eclipse of the tail, by intercept-
ing the sun*s rays rf consequently, the tail, as well
as the head, shines with a borrowed light, and both
are visible, only by reflecting the rays of the sun.

As the consideration of the properties of the elec-
tric element was introduced, merely, to illustrate the
several propositions, and the conclusions resulting
from them, contained in the foregoing pages ; it was
thought proper to add thus much upon that subject,
in order to prevent the framing an hypothesis from
those properties, which, instead of removing the fears
of the timorous, upon the appearance of a Comet,
(which was one design of this essay,) would natu-

• Franklin's letter's, page 116 and 129.
^ f Hevelii Cometographia Lib, xii. pag-e 898, quoted by Mr.
Professor Wiothrop in his 2d Lecture on Comets.



ON COMETS. 117

rally tend to increase their apprehensions. Whereas,
upon the principles we have endeavoured to establish,
the tails of Comets appear to be nothing more than
air, immensely expanded and rarefied; through
which the earth might pass, with the utmost safety
to its inhabitants. And, instead of these bodies being
heralds, sent fourth to denounce the wrath of heaven,
in which light they have been considered by the ig-
norant and superstitious, of all ages ; or the imme-
diate executioners of divine vengeance, as others have
apprehended ; we shall endeavour to prove, in the
following pages, that comets deserve to be considered
in a more respectable light ; and that their tails, how-
ever awful and portentous they have been esteemed
by some ; may be designed for, and are wisely adapted
to, the truly god-like purposes, of rendering habita-
ble a vast variety of worlds ; and of affording a co7w-
fortable subsistence to innumerable species of beings,
by which they are, probably, inhabited.



ESSAY ON COMETS.



PART II.

As ancient geographers imagined the polar and
equatorial regions, or the frigid and torrid zones of
the earth, were uninhabitable, in consequence of the
extremes of heat and cold, to which those climates are
exposed : so, modern astronomers have passed a si-
milar judgment upon the superior and inferior planets,
especially on Saturn and Mercury ; concluding, that
our water would always boil upon the latter, and be
frozen upon the former ; and that merely in conse-
quence of their different distances from the sun.*
Whence it has been naturally concluded, that the
textures of their various fluids, and of their inhabi-
tants, to whose uses these fluids are adapted, are very-
different from what they are found to be upon our
earth : and, considering the near approaches of most
Comets /o, and the vast elongations of all their orbits
from the sun, it has been generally supposed, that no
material race of beings could subsist under such
amazing vicissitudes of heat and coid, as those bodies

* See Newt, princip. Book lii. Prop. viii. Cor. 4.



120 ON COMETS.

must, from their different situations, necessarily be
exposed to ; consequently that they are uninhabited.

But the conclusiveness of ihis reasoning depends
upon the truth of the following proposition ; advanced
indeed by Sir Isaac JVewton ; but not supported by
experiments, which were, with him, the criterion vc-
ritatis ; viz. that, " The heat of the sun is as the density
" of his rays^ that is recifirocally as the squares of the dis-
" tances from the sun."*

Here, we are again reduced to the disagreeable ne-
cessity, of dissenting from the opinion of the greatest
GENIUS that ever dignified human reason ; which,
considering the justly celebrated fame of that illus-
trious author, may be stigmatized as ignorance or va-
nity: but it is hoped that the reader will wave that
imputation, if he shall judge, upon the whole, that Sir
Isaac himself would have altered his opinion, upon
the evidence which we shall produce in support of the
contrary position : w^e may, however, lay down this as
a maxim, that, in the prosecution of any science, the
progress of the mind must necessarily be retarded,
in proportion to the implicit assent we give to the de-
cisions of any man, however great. We shall there-
fore, without further apology, endeavour to prove
that the heat of the sun, as perceived by us, and as
discoverable by its effects upon other substances ex-
posed to his rays, does not depend upon the density
of those rays onUj^ though they are necessary to the
very existence of that heat; but, equcdlij upon the

* Princip. under Prop. xli. Book iii.



ON COMETS. 121

concurrent operation of another cause, which we shall
presently consider; from whence it will follow, that
these causes, wherever they co-exist, whether upon
the earth, or upon the heavenly bodies, will naturally
produce similar effects.

In the mean time, before we engage in the discussion
of planetary heat, as depending upon th& several dis-
tances of the planets from the sun ; it may throw some
light upon this subject if we consider the portion of
that heat which falls to our own share, and the distribu-
tion of it throughout the various climates of the earth.

The surface of the earth has, by geographers, been
divided into five zones, viz. one torrid^ including all the
regions between the tropics, upon every part of which
the sun shines perpendicularly twice every year: Two
frigid^ which are situated between the polar-circles
and the poles, and endure the rigours of perpetual
winter, as the former is always basking in a summer
sun; And two tcmjierate^ which experience the vicis-
situdes of winter and summer, and, in some parts of
them, in their extremes ; these are situated between
the frigid and to'rrid zontSy in both hemispheres. In
the first of these, the seasons are much more uniform
than in the others, the days and nights being nearly
of equal lengths, the year round; and although the
heat may, for a constancy, be greater therein than in
any other climate, yet it is not lie^ble to such great and
sudden changes as are experienced in the temperate
zones ; for, during a whole annual revolution of the
earth, the difference of the degrees of heat, expe-
II



122 ON COMETS.

rienced in the torrid zone, as determined by the ther-
mometer, are not so great as those which, sometimes,
happen in the temjierate zones, within the compass of
a few hours :* Much more do they fall short of the
extremes which are endured in the latter, in the op-
posite seasons of the year.f But what is above assert-
ed of the torrid zone is to be understood only of the

* One morning, in the winter of 1768, the mercury in Faren- ^
Zie/«'j thermometer was 5*^ below 0°; by 11 o'clock the same day
it had risen to 30°, and the next day to above 60*^ ; the diffe-
rence being 65° in little more than 24 hours. Again, May 30,
1764, when the general election for the choice of counsellors,
for this province, was held at Concordy (a town about 20 miles
west from Boston) the weather was (for the season) extremely
hot J but on the morning of the 1st June following, a severe frost
cut off' all the Indian corn, beans and other tender annual vege-
tables, in that and the towns adjacent, for miles round. And
on one Sunday morning, in the winter of 1759-60, a transition
was made, instantaneously, from severe cold to summer heat ;
to the great surprise of every one, and to the no small terror
of many. The buildings suddenly smoked to such a degree,
that, in some of the worshipping assemblies at Boston^ the peo-
ple suspected that the neighbouring houses were on fire ; and
there was scarely a person, who did not recoil from the heat,
at the church doors, at the close of the service.

f One summer's afternoon in the year 1760, the thermome-
ter, being exposed to the open air, in the shade, the mercury
stood at 102°. At another time, viz. in the winter of 1766-67,
the sun being an hour high in the morning, it was at 9° below
0°. These were probably, as great extremes as have been ob-
served In this climate, the difference being 111° by the ther-
mometer.



ON COMETS. 123

low, inhabited and cultivated countries, the mountain-
ous regions with which those climates abound being
excepted, for reasons which will hereafter appear.

The axes of the several planets whose diurnal ro-
tations have been discovered are inclined, more or
less, to the planes of their respective orbits ; conse-
quently, their superficies are divisible into zones and
climates, corresponding with those of the earth : And
it is, at least, highly probable, that the various cli-
mates of each globe, during its periodical revolution
round the sun, experience as great vicissitudes of heat
and cold as those of the earth : Nor is it unlikely that,
in the equatorial regions of the different planets, there
maybe at the same time as great varieties in the
degrees of heat they respectively enjoy, as there are
in the temperate zones of the earth in the different
seasons of the year; but supposing all this, the ine-
qualities in the distribution of heat to the several pla-
nets and their various climates would vanish, when
compared with those extremes which they would ne-
cessarily be exposed to, at their several distances
from the sun, upon the supposition that the sun's heat
were as the density of his rays ; for were that really
the case, the heat of summer upon Mercury would be.
about seven times as great as upon the earth, and
above twice as hot as boiling water with us. On the
other hand our summer heat would be above ninety
times greater than that of Saturn^ the difference being-
more than seven times as great as that between our



124 ON COMETS.

summer heat and the heat of red hot iron :* For it is
undoubtedly certain, that the density of the sun's
rays is reciprocally as the squares of the distances
from the sun ; from whence the above conclusions
must necessarily follow, if the heat be proportional to
that density.

It is certainly then a question well deserving a phi-
losophical inquiry; whether there be not some me-
dium provided in nature, which, being distributed in
different proportions to the several planets, may so
attemper the heat of the sun to their respective dis-
tances from him, as that the inhabitants of all may be
equally happy in the enjoyment of it; and that one
globe may receive as much benefit, and be exposed
to as little injury, from that heat, as any other through-
out the system. This indeed seems to be an object
so worthy of the attention and providence of the great
PARENT of the universe, that a philosophic mind would
naturally embrace such an hypothesis, had it, but, the
most slender evidence to support it. This medium,
we shall find, is actually provided in the element of
air, which is, in various proportions, condensed round,
and constitutes the atmospheres of the earth and the
heavenly bodies.

As air is an element, to which we, and probably
the inhabitants of the other planets, are more indebt-
ed than is generally imagined ; a short dissertation

* Sh' /. Ncivton concludes from experiments thr.t boiling
water is tiirec times, and red iiot iron about twelve times liot-
ter than our summer beat. Frincip. Prop. XLI. Book HI,



ON COMETS. 125

upon some of the advantages which accrue to us, and
probably to them, from its presence, may be accepta-
ble to the reader.

Air is a grand medium in nature, through which
an all-bountiful providence conveys to us many of the
conveniences, comforts, and delights of life. Upon
air depends the ascent of vapours, and their conden-
sation into clouds, whence they descend in dews and
grateful showers, to refresh and fructify the earth.—
Upon air we depend for the twilight, which affords
us an agreeable gradation of shades from day to night ;
without which we should instantaneously plunge from
the light of the sun to midnight darkness ; and again
emerge from total darkness to the full lustre of day;
which would be insufferable to our organs of sight,
upon their present constructure. Air is also the ve-
hicle of sounds, whether articulate or inarticulate ;
consequently without it, we should not only be de-
prived of the artless melody of the woods, and of the
raptures which accompany the masterly execution of
musical composition ; but, (which is of infinitely
greater importance to us) there could be no language,
no communication of ideas, but by dumb signs ; no
liberal arts nor sciences in the world. Therefore if
we could subsist without this element, all mankind
would be like the unhappy few among us who are
said to be born deaf and dumb.

It has already been shewn from experiments, that
air is necessary both to the support of animal life, and
to the subsistance of flame : and how far the very
*11



126 ON COMETSi

being- of fire, in any shape, and even of heat itself,
may depend upon it, the reader may judge from the
following experiments and observations of Mr. Boyle,
related in Shaiv^s abridgement of his works.

" Coals," says Mr. Boyle, " being put glowing into a
" receiver, in three minutes after beginning to pump,
" the fire totally disappeared. — Other coals being
*' suspended, in the open air, at the same time, con-
" tinued burning until a great part was reduced to
^' ashes,* Lighted match was found more difficult
*' to put out by exhausting the air than kindled
'' charcoal, nevertheless in about seven minutes the
" fire was extinguished, beyond the possibility of re-
" covery by re-admitting fresh air." Here we see
that air is necessary to the subsistance, not only of
flame, but of fire that emits no flame at all. To these
we may add an easy experiment, which any person
may try at his leisure, without the assistance of a
pneumatic engine, viz. A composition may be made


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Online LibraryJohn WinthropTwo lectures on comets → online text (page 9 of 14)