have a right information, is for me to; it being then pretty cool for
the season and climate; and this is worth remark, because cool air
is weighty, and will not ascend; besides, when the air grows cool,
it shews that the upper region descends, and conveys this temper
down; and when the tempers are equal, no whirlwind can take place.
But spouts have been known, when the lower region has been really
cold. Gordon's spout in the Downs is an instance of this--(_Vide_
_Philosophical Transactions_)--where the upper region was probably
not at all cooler, if so cold as the lower: it was a cold day in the
month of March, hail followed, but not snow, and it is observable,
that not so much as hail follows or accompanies them in moderate
seasons or climes, when and where they are most frequent. However,
it is not improbable, that just about the place of descent may be
cooler than the neighbouring parts, and so favour the wonderful
celerity of condensation. But, after all, should we allow the under
region to be ever so much the hottest, and a whirlwind to take place
in it: suppose then the sea-water to ascend, it would certainly cool
the spout, and then, query, whether it would not very much, if not
wholly, obstruct its progress.
It commonly rains when spouts disappear, if it did not before, which
it frequently does not, by the best accounts I have had; but the
cloud encreases much faster after they disappear, and it soon rains.
The first shews the spout to be a contracted rain, instead of the
diffused one that follows; and the latter that the cloud was not
formed by ascending water, for then it would have ceased growing when
the spout vanished.
However, it seems that spouts have sometimes appeared after it began
to rain; but this is one way a proof of my hypothesis, viz. as
whirlwinds do not come under a cloud.
I forgot to mention, that the increase of cloud, while the spout
subsists, is no argument of an ascent of water, by the spout. Since
thunder-clouds sometimes encrease greatly while it rains very hard.
Divers effects of spouts seem not so well accounted for any other way
as by descent.
The bush round the feet of them seems to be a great spray of water
made by the violence of descent, like that in great falls of water
from high precipices.
The great roar, like some vast inland falls, is so different from the
roar of whirlwinds, by all acounts, as to be no ways compatible.
The throwing things from it with great force, instead of carrying
them up into the air, is another difference.
There seems some probability that the sailors traditionary belief,
that spouts may break in their decks, and so destroy vessels, might
originate from some facts of that sort in former times. This danger
is apparent on my hypothesis, but it seems not so on the other:
and my reason for it is, that the whole column of a spout from the
sea to the clouds, cannot, in a natural way, even upon the largest
supposition, support more than about three feet water, and from truly
supposeable causes, not above one foot, as may appear more plainly
by and by. Supposing now the largest of these quantities to rise, it
must be disseminated into drops, from the surface of the sea to the
region of the clouds, or higher; for this reason it is quite unlikely
to be collected into masses, or a body, upon its falling; but would
descend in progression according to the several degrees of altitude
the different portions had arrived at when it received this new
determination.
Now that there cannot more rise upon the common hypothesis than
I have mentioned, may appear probable, if we attend to the only
efficient cause in supposed ascending spouts, viz. whirlwinds.
We know that the rarefaction of the lower, and the condensation of
the upper region of air, are the only natural causes of whirlwinds.
Let us then suppose the former as hot as their greatest summer heat
in England, and the latter as cold as the extent of their winter.
These extremes have been found there to alter the weight of the air
one-tenth, which is equal to a little more than three feet water.
Were this case possible, and a whirlwind take place in it, it might
act with a force equal to the mentioned difference. But as this is
the whole strength, so much water could not rise; therefore to allow
it due motion upwards, we must abate, at least, one-fourth part,
perhaps more, to give it such a swift ascension as some think usual.
But here several difficulties occur, at least they are so to me. As,
whether this quantity would render the spout opaque? since it is
plain that in drops it could not do so. How, or by what means it may
be reduced small enough? or, if the water be not reduced into vapour,
what will suspend it in the region of the clouds when exonerated
there? And, if vapourized while ascending, how can it be dangerous by
what they call the breaking? For it is difficult to conceive how a
condensative power should instantaneously take place of a rarefying
and disseminating one.
The sudden fall of the spout, or rather, the sudden ceasing of it, I
accounted for, in my way, before. But it seems necessary to mention
something I then forgot. Should it be said to do so (_i. e._) to
fall, because all the lower rarefied air is ascended, whence the
whirlwind must cease, and its burden drop; I cannot agree to this,
unless the air be observed on a sudden to have grown much colder,
which I cannot learn has been the case. Or should it be supposed that
the spout was, on a sudden, obstructed at the top, and this the cause
of the fall, however plausible this might appear, yet no more water
would fall than what was at the same time contained in the column,
which is often, by many and satisfactory accounts to me, again far
from being the case.
We are, I think, sufficiently assured, that not only tons, but scores
or hundreds of tons descend in one spout. Scores of tons more than
can be contained in the trunk of it, should we suppose water to
ascend.
But, after all, it does not appear that the above-mentioned different
degrees of heat and cold concur in any region where spouts usually
happen, nor, indeed, in any other.
_Observations on the Meteorological Paper; by a Gentleman in
Connecticut._
Read at the Royal Society, Nov. 4, 1756.
"Air and water mutually attract each other, (saith Mr. F.) hence
water will dissolve in air, as salt in water." I think that he hath
demonstrated, that the supporting of salt in water is not owing to
its superficies being increased, because "the specific gravity of
salt is not altered by dividing of it, any more than that of lead,
sixteen bullets of which, of an ounce each, weigh as much in water
as one of a pound." But yet, when this came to be applied to the
supporting of water in air, I found an objection rising in my mind.
In the first place, I have always been loth to seek for any new
hypothesis, or particular law of nature, to account for any thing
that may be accounted for from the known, general, and universal law
of nature; it being an argument of the infinite wisdom of the author
of the world, to effect so many things by one general law. Now I
had thought that the rising and support of water in air, might be
accounted for from the general law of gravitation, by only supposing
the spaces occupied by the same quantity of water increased.
And, with respect to the lead, I queried thus in my own mind; whether
if the superficies of a bullet of lead should be increased four or
five fold by an internal vacuity, it would weigh the same in water
as before. I mean, if a pound of lead should be formed into a hollow
globe, empty within, whose superficies should be four or five times
as big as that of the same lead when a solid lump, it would weigh as
much in water as before. I supposed it would not. If this concavity
was filled with water, perhaps it might; if with air, it would weigh
at least as much less, as this difference between the weight of that
included air, and that of water.
Now although this would do nothing to account for the dissolution
of salt in water, the smallest lumps of salt being no more hollow
spheres, or any thing of the like nature than the greatest; yet,
perhaps, it might account for water's rising and being supported in
air. For you know that such hollow globules, or bubbles, abound upon
the surface of the water, which even by the breath of our mouths, we
can cause to quit the water, and rise in the air.
These bubbles I used to suppose to be coats of water, containing
within them air rarefied and expanded with fire, and that, therefore,
the more friction and dashing there is upon the surface of the
waters, and the more heat and fire, the more they abound.
And I used to think, that although water be specifically heavier than
air, yet such a bubble, filled only with fire and very rarefied air,
may be lighter than a quantity of common air, of the same cubical
dimensions, and, therefore, ascend; for the rarefied air inclosed,
may more fall short of the same bulk of common air, in weight, than
the watery coat exceeds a like bulk of common air in gravity.
This was the objection in my mind, though, I must confess, I know
not how to account for the watery coat's encompassing the air, as
above-mentioned, without allowing the attraction between air and
water, which the gentleman supposes; so that I do not know but
that this objection, examined by that sagacious genius, will be an
additional confirmation of the hypothesis.
The gentleman observes, "that a certain quantity of moisture should
be every moment discharged and taken away from the lungs; and
hence accounts for the suffocating nature of snuffs of candles, as
impregnating the air with grease, between which and water there is
a natural repellency; and of air that hath been frequently breathed
in, which is overloaded with water, and, for that reason, can take
no more air. Perhaps the same observation will account for the
suffocating nature of damps in wells."
But then if the air can support and take off but such a proportion of
water, and it is necessary that water be so taken off from the lungs,
I queried with myself how it is we can breathe in an air full of
vapours, so full as that they continually precipitated. Do not we see
the air overloaded, and casting forth water plentifully when there is
no suffocation?
The gentleman again observes, "That the air under the equator, and
between the tropics, being constantly heated and rarefied by the
sun, rises; its place is supplied by air from northern and southern
latitudes, which, coming from parts where the air and earth had
less motion, and not suddenly acquiring the quicker motion of the
equatorial earth, appears an east wind blowing westward; the earth
moving from west to east, and slipping under the air."
In reading this, two objections occurred to my mind:
First, that it is said, the trade-wind doth not blow in the forenoon,
but only in the afternoon.
Secondly, that either the motion of the northern and southern air
towards the equator is so slow, as to acquire almost the same motion
as the equatorial air when it arrives there, so that there will be no
sensible difference; or else the motion of the northern and southern
air towards the equator, is quicker, and must be sensible; and then
the trade-wind must appear either as a south-east or north-east wind:
south of the equator, a south-east wind; north of the equator, a
north-east. For the apparent wind must be compounded of this motion
from north to south, or _vice versa_; and of the difference between
its motion from west to east, and that of the equatorial air.
_Observations in Answer to the foregoing, by B. Franklin._
Read at the Royal Society, Nov. 4, 1756.
1st. The supposing a mutual attraction between the particles of water
and air is not introducing a new law of nature; such attractions
taking place in many other known instances.
2dly. Water is specifically 850 times heavier than air. To render a
bubble of water, then, specifically lighter than air, it seems to me
that it must take up more than 850 times the space it did before it
formed the bubble; and within the bubble should be either a vacuum
or air rarefied more than 850 times. If a vacuum, would not the
bubble be immediately crushed by the weight of the atmosphere? And no
heat, we know of, will rarefy air any thing near so much; much less
the common heat of the sun, or that of friction by the dashing on
the surface of the water. Besides, water agitated ever so violently
produces no heat, as has been found by accurate experiments.
3dly. A hollow sphere of lead has a firmness and consistency in it,
that a hollow sphere or bubble of fluid unfrozen water cannot be
supposed to have. The lead may support the pressure of the water it
is immersed in, but the bubble could not support the pressure of the
air, if empty within.
4thly. Was ever a visible bubble seen to rise in air? I have made
many, when a boy, with soap-suds and a tobacco-pipe; but they all
descended when loose from the pipe, though slowly, the air impeding
their motion. They may, indeed, be forced up by a wind from below,
but do not rise of themselves, though filled with warm breath.
5thly. The objection relating to our breathing moist air seems
weighty, and must be farther considered. The air that has been
breathed has, doubtless, acquired an addition of the perspirable
matter which nature intends to free the body from, and which would be
pernicious if retained and returned into the blood; such air then may
become unfit for respiration, as well for that reason, as on account
of its moisture. Yet I should be glad to learn, by some accurate
experiment, whether a draft of air, two or three times inspired,
and expired, perhaps in a bladder, has, or has not, acquired more
moisture than our common air in the dampest weather. As to the
precipitation of water in the air we breathe, perhaps it is not
always a mark of that air's being overloaded. In the region of the
clouds, indeed, the air must be overloaded if it lets fall its water
in drops, which we call rain; but those drops may fall through a
drier air near the earth; and accordingly we find that the hygroscope
sometimes shews a less degree of moisture, during a shower, than
at other times when it does not rain at all. The dewy dampness,
that settles on the insides of our walls and wainscots, seems more
certainly to denote an air overloaded with moisture; and yet this is
no sure sign: for, after a long continued cold season, if the air
grows suddenly warm, the walls, &c. continuing longer their coldness,
will, for some time, condense the moisture of such air, till they
grow equally warm, and then they condense no more, though the air is
not become drier. And, on the other hand, after a warm season, if the
air grows cold, though moister than before, the dew is not so apt to
gather on the walls. A tankard of cold water will, in a hot and dry
summer's day, collect a dew on its outside; a tankard of hot water
will collect none in the moistest weather.
6thly. It is, I think, a mistake that the trade-winds blow only in
the afternoon. They blow all day and all night, and all the year
round, except in some particular places. The southerly sea-breezes
on your coasts, indeed, blow chiefly in the afternoon. In the very
long run from the west side of America to Guam, among the Philippine
Islands, ships seldom have occasion to hand their sails, so equal
and steady is the gale, and yet they make it in about 60 days, which
could not be if the wind blew only in the afternoon.
7thly. That really is, which the gentleman justly supposes ought to
be on my hypothesis. In sailing southward, when you first enter the
trade-wind, you find it north-east, or thereabouts, and it gradually
grows more east as you approach the line. The same observation is
made of its changing from south-east to east gradually, as you come
from the southern latitudes to the equator.
_Observations on the Meteorological Paper; sent by a Gentleman[10]
in New-York to B. Franklin._
Read at the Royal Society, Nov. 4, 1756.
That power by which the air expands itself, you attribute to a mutual
repelling power in the particles which compose the air, by which
they are separated from each other with some degree of force: now
this force, on this supposition, must not only act when the particles
are in mutual contact, but likewise when they are at some distance
from each other. How can two bodies, whether they be great or small,
act at any distance, whether that distance be small or great, without
something intermediate on which they act? For if any body act on
another, at any distance from it, however small that distance be,
without some medium to continue the action, it must act where it is
not, which to me seems absurd.
It seems to me, for the same reason, equally absurd to give a mutual
attractive power between any other particles supposed to be at a
distance from each other, without any thing intermediate to continue
their mutual action. I can neither attract nor repel any thing at a
distance, without something between my hand and that thing, like a
string, or a stick; nor can I conceive any mutual action without some
middle thing, when the action is continued to some distance.
The encrease of the surface of any body lessens its weight, both in
air, and water, or any other fluid, as appears by the slow descent of
leaf-gold in the air.
The observation of the different density of the upper and lower
air, from heat and cold, is good, and I do not remember it is taken
notice of by others; the consequences also are well drawn; but as to
winds, they seem principally to arise from some other cause. Winds
generally blow from some large tracts of land, and from mountains.
Where I live, on the north side of the mountains, we frequently have
a strong southerly wind, when they have as strong a northerly wind,
or calm, on the other side of these mountains. The continual passing
of vessels on Hudson's River, through these mountains, give frequent
opportunities of observing this.
In the spring of the year the sea-wind (by a piercing cold) is always
more uneasy to me, accustomed to winds which pass over a tract of
land, than the north-west wind.
You have received the common notion of water-spouts, which, from my
own ocular observation, I am persuaded is a false conception. In a
voyage to the West-Indies, I had an opportunity of observing many
water-spouts. One of them passed nearer than thirty or forty yards to
the vessel I was in, which I viewed with a good deal of attention;
and though it be now forty years since I saw it, it made so strong
an impression on me, that I very distinctly remember it. These
water-spouts were in the calm latitudes, that is, between the trade
and the variable winds, in the month of July. That spout which passed
so near us was an inverted cone, with the _tip_ or _apex_ towards
the sea, and reached within about eight feet of the surface of the
sea, its basis in a large black cloud. We were entirely becalmed. It
passed slowly by the vessel. I could plainly observe, that a violent
stream of wind issued from the spout, which made a hollow of about
six feet diameter in the surface of the water, and raised the water
in a circular uneven ring round the hollow, in the same manner that a
strong blast from a pair of bellows would do when the pipe is placed
perpendicular to the surface of the water; and we plainly heard the
same hissing noise which such a blast of wind must produce on the
water. I am very sure there was nothing like the sucking of water
from the sea into the spout, unless the spray, which was raised in a
ring to a small height, could be mistaken for a raising of water. I
could plainly distinguish a distance of about eight feet between the
sea and the tip of the cone, in which nothing interrupted the sight,
which must have been, had the water been raised from the sea.
In the same voyage I saw several other spouts at a greater distance,
but none of them whose tip of the cone came so near the surface of
the water. In some of them the axis of the cone was considerably
inclined from the perpendicular, but in none of them was there the
least appearance of sucking up of water. Others of them were bent
or arched. I believe that a stream of wind issued from all of them,
and it is from this stream of wind that vessels are often overset,
or founder at sea suddenly. I have heard of vessels being overset
when it was perfectly calm, the instant before the stream of wind
struck them, and immediately after they were overset; which could not
otherwise be but by such a stream of wind from a cloud.
That wind is generated in clouds will not admit of a dispute. Now if
such wind be generated within the body of the cloud, and issue in
one particular place, while it finds no passage in the other parts
of the cloud, I think it may not be difficult to account for all the
appearances in water-spouts; and from hence the reason of breaking
those spouts, by firing a cannon-ball through them, as thereby a
horizontal vent is given to the wind. When the wind is spent, which
dilated the cloud, or the fermentation ceases, which generates the
air and wind, the clouds may descend in a prodigious fall of water
or rain. A remarkable intestine motion, like a violent fermentation,
is very observable in the cloud from whence the spout issues. No
salt-water, I am persuaded, was ever observed to fall from the
clouds, which must certainly have happened if sea-water had been
raised by a spout.
FOOTNOTE:
[10] Mr. Cadwallader Colden. _Editor._
_Answer to the foregoing Observations, by B. Franklin._
Read at the Royal Society, NOV. 4, 1756.
I agree with you, that it seems absurd to suppose that a body can act
where it is not. I have no idea of bodies at a distance attracting or
repelling one another without the assistance of some medium, though
I know not what that medium is, or how it operates. When I speak of
attraction or repulsion, I make use of those words for want of others
more proper, and intend only to express _effects_ which I see, and
not _causes_ of which I am ignorant. When I press a blown bladder
between my knees, and find I cannot bring its sides together, but my
knees feel a springy matter, pushing them back to a greater distance,
or repelling them, I conclude that the air it contains is the cause.
And when I operate on the air, and find I cannot by pressure force
its particles into contact, but they still spring back against the
pressure, I conceive there must be some medium between its particles
that prevents their closing, though I cannot tell what it is. And
if I were acquainted with that medium, and found its particles to
approach and recede from each other, according to the pressure they
suffered, I should imagine there must be some finer medium between
them, by which these operations were performed.
I allow that increase of the surface of a body may occasion it
to descend slower in air, water, or any other fluid; but do not
conceive, therefore, that it lessens its weight. Where the increased
surface is so disposed as that in its falling a greater quantity
of the fluid it sinks in must be moved out of its way, a greater
time is required for such removal. Four square feet of sheet-lead
sinking in water _broadways_, cannot descend near so fast as it
would _edgeways_, yet its weight in the hydrostatic balance would,
I imagine, be the same, whether suspended by the middle or by the
corner.
I make no doubt but that ridges of high mountains do often interrupt,
stop, reverberate, or turn the winds that blow against them,
according to the different degrees of strength of the winds, and
angles of incidence. I suppose, too, that the cold upper parts of
mountains may condense the warmer air that comes near them, and so by
making it specifically heavier, cause it to descend on one or both
sides of the ridge into the warmer valleys, which will seem a wind
blowing from the mountain.