volatile, salt remains fixed in the fire, and no heat can force it up to
any considerable height, or oblige the air to hold it. Hence, when salt
rises, as it will a little way, into air with water, there is instantly
a separation made; the particles of water adhere to the air, and the
particles of salt fall down again, as if repelled and forced off from
the water by some power in the air; or, as some metals, dissolved in a
proper _menstruum_, will quit the solvent when other matter approaches,
and adhere to that, so the water quits the salt and embraces the air;
but air will not embrace the salt and quit the water, otherwise our
rains would indeed be salt, and every tree and plant on the face of the
earth be destroyed, with all the animals that depend on them for
subsistence. He who hath proportioned and given proper quantities to all
things, was not unmindful of this. Let us adore Him with praise and
thanksgiving.
By some accounts of seamen, it seems the column of water W W sometimes
falls suddenly; and if it be, as some say, fifteen or twenty yards
diameter, it must fall with great force, and they may well fear for
their ships. By one account, in the _Transactions_, of a spout that fell
at Colne, in Lancashire, one would think the column is sometimes lifted
off from the water and carried over land, and there let fall in a body;
but this, I suppose, happens rarely.
Stuart describes his spouts as appearing no bigger than a mast, and
sometimes less; but they were seen at a league and a half distance.
I think I formerly read in Dampier, or some other voyager, that a spout,
in its progressive motion, went over a ship becalmed on the coast of
Guinea, and first threw her down on one side, carrying away her
foremast, then suddenly whipped her up, and threw her down on the other
side, carrying away her mizen-mast, and the whole was over in an
instant. I suppose the first mischief was done by the foreside of the
whirl, the latter by the hinderside, their motion being contrary.
I suppose a whirlwind or spout may be stationary when the concurring
winds are equal; but if unequal, the whirl acquires a progressive motion
in the direction of the strongest pressure.
When the wind that gives the progressive motion becomes stronger below
than above, or above than below, the spout will be bent, and, the cause
ceasing, straighten again.
Your queries towards the end of your paper appear judicious and worth
considering. At present I am not furnished with facts sufficient to
make any pertinent answer to them, and this paper has already a
sufficient quantity of conjecture.
Your manner of accommodating the accounts to your hypothesis of
descending spouts is, I own, in ingenious, and perhaps that hypothesis
may be true. I will consider it farther, but, as yet, I am not satisfied
with it, though hereafter I may be.
Here you have my method of accounting for the principal phenomena, which
I submit to your candid examination.
And as I now seem to have almost written a book instead of a letter, you
will think it high time I should conclude; which I beg leave to do, with
assuring you that I am, &c.,
B. FRANKLIN.
* * * * *
_Alexander Small, London._
ON THE NORTHEAST STORMS IN NORTH AMERICA.
May 12, 1760.
Agreeable to your request, I send you my reasons for thinking that our
northeast storms in North America begin first, in point of time, in the
southwest parts; that is to say, the air in Georgia, the farthest of our
colonies to the southwest, begins to move southwesterly before the air
of Carolina, which is the next colony northeastward; the air of Carolina
has the same motion before the air of Virginia, which lies still more
northeastward; and so on northeasterly through Pennsylvania, New-York,
New-England, &c., quite to Newfoundland.
These northeast storms are generally very violent, continue sometimes
two or three days, and often do considerable damage in the harbours
along the coast. They are attended with thick clouds and rain.
What first gave me this idea was the following circumstance. About
twenty years ago, a few more or less, I cannot from my memory be
certain, we were to have an eclipse of the moon at Philadelphia, on a
Friday evening, about nine o'clock. I intended to observe it, but was
prevented by a northeast storm, which came on about seven, with thick
clouds as usual, that quite obscured the whole hemisphere. Yet when the
post brought us the Boston newspaper, giving an account of the effects
of the same storm in those parts, I found the beginning of the eclipse
had been well observed there, though Boston lies N. E. of Philadelphia
about four hundred miles. This puzzled me, because the storm began with
us so soon as to prevent any observation; and being a northeast storm, I
imagined it must have begun rather sooner in places farther to the
northeastward than it did at Philadelphia. I therefore mentioned it in a
letter to my brother, who lived at Boston; and he informed me the storm
did not begin with them till near eleven o'clock, so that they had a
good observation of the eclipse; and upon comparing all the other
accounts I received from the several colonies of the time of beginning
of the same storm, and, since that, of other storms of the same kind, I
found the beginning to be always later the farther northeastward. I have
not my notes with me here in England, and cannot, from memory, say the
proportion of time to distance, but I think it is about an hour to every
hundred miles.
From thence I formed an idea of the cause of these storms, which I would
explain by a familiar instance or two. Suppose a long canal of water
stopped at the end by a gate. The water is quite at rest till the gate
is open, then it begins to move out through the gate; the water next the
gate is first in motion, and moves towards the gate; the water next to
that first water moves next, and so on successively, till the water at
the head of the canal is in motion, which is last of all. In this case
all the water moves, indeed, towards the gate, but the successive times
of beginning motion are the contrary way, viz., from the gate backward
to the head of the canal. Again, suppose the air in a chamber at rest,
no current through the room till you make a fire in the chimney.
Immediately the air in the chimney, being rarefied by the fire, rises;
the air next the chimney flows in to supply its place, moving towards
the chimney; and, in consequence, the rest of the air successively,
quite back to the door. Thus, to produce our northeast storms, I suppose
some great heat and rarefaction of the air in or about the Gulf of
Mexico; the air, thence rising, has its place supplied by the next more
northern, cooler, and, therefore, denser and heavier air; that, being in
motion, is followed by the next more northern air, &c., in a successive
current, to which current our coast and inland ridge of mountains give
the direction of northeast, as they lie N. E. and S. W.
This I offer only as an hypothesis to account for this particular fact;
and perhaps, on farther examination, a better and truer may be found. I
do not suppose all storms generated in the same manner. Our northwest
thunder-gusts in America, I know, are not; but of them I have written my
opinion fully in a paper which you have seen.
B. FRANKLIN.
* * * * *
_To Dr. Lining, at Charleston._
ON COLD PRODUCED BY EVAPORATION.
New-York, April 14, 1757.
It is a long time since I had the pleasure of a line from you; and,
indeed, the troubles of our country, with the hurry of business I have
been engaged in on that account, have made me so bad a correspondent,
that I ought not to expect punctuality in others.
But, being about to embark for England, I could not quit the continent
without paying my respects to you, and, at the same time, taking leave
to introduce to your acquaintance a gentleman of learning and merit,
Colonel Henry Bouquet, who does me the favour to present you this
letter, and with whom I am sure you will be much pleased.
Professor Simpson, of Glasgow, lately communicated to me some curious
experiments of a physician of his acquaintance, by which it appeared
that an extraordinary degree of cold, even to freezing, might be
produced by evaporation. I have not had leisure to repeat and examine
more than the first and easiest of them, viz.: wet the ball of a
thermometer by a feather dipped in spirits of wine which has been kept
in the same room, and has, of course, the same degree of heat or cold.
The mercury sinks presently three or four degrees, and the quicker if,
during the evaporation, you blow on the ball with bellows; a second
wetting and blowing, when the mercury is down, carries it yet lower. I
think I did not get it lower than five or six degrees from where it
naturally stood, which was at that time sixty. But it is said that a
vessel of water, being placed in another somewhat larger, containing
spirit, in such a manner that the vessel of water is surrounded with the
spirit, and both placed under the receiver of an airpump; on exhausting
the air, the spirit, evaporating, leaves such a degree of cold as to
freeze the water, though the thermometer in the open air stands many
degrees above the freezing point.
I know not how this phenomena is to be accounted for, but it gives me
occasion to mention some loose notions relating to heat and cold, which
I have for some time entertained, but not yet reduced into any form.
Allowing common fire, as well as electrical, to be a fluid capable of
permeating other bodies and seeking an equilibrium, I imagine some
bodies are better fitted by nature to be conductors of that fluid than
others; and that, generally, those which are the best conductors of the
electric fluid are also the best conductors of this; and _è contra_.
Thus a body which is a good conductor of fire readily receives it into
its substance, and conducts it through the whole to all the parts, as
metals and water do; and if two bodies, both good conductors, one
heated, the other in its common state, are brought into contact with
each other, the body which has most fire readily communicates of it to
that which had least, and that which had least readily receives it, till
an equilibrium is produced. Thus, if you take a dollar between your
fingers with one hand, and a piece of wood of the same dimensions with
the other, and bring both at the same time to the flame of a candle, you
will find yourself obliged to drop the dollar before you drop the wood,
because it conducts the heat of the candle sooner to your flesh. Thus,
if a silver teapot had a handle of the same metal, it would conduct the
heat from the water to the hand, and become too hot to be used; we
therefore give to a metal teapot a handle of wood, which is not so good
a conductor as metal. But a China or stone teapot, being in some degree
of the nature of glass, which is not a good conductor of heat, may have
a handle of the same stuff. Thus, also, a damp, moist air shall make a
man more sensible of cold, or chill him more than a dry air that is
colder, because a moist air is fitter to receive and conduct away the
heat of his body. This fluid, entering bodies in great quantity, first
expands them, by separating their parts a little; afterward, by farther
separating their parts, it renders solids fluid, and at length
dissipates their parts in air. Take this fluid from melted lead or from
water, the parts cohere again; the first grows solid, the latter becomes
ice: and this is sooner done by the means of good conductors. Thus, if
you take, as I have done, a square bar of lead, four inches long and
one inch thick, together with three pieces of wood planed to the same
dimensions, and lay them on a smooth board, fixed so as not to be easily
separated or moved, and pour into the cavity they form as much melted
lead as will fill it, you will see the melted lead chill and become firm
on the side next the leaden bar some time before it chills on the other
three sides in contact with the wooden bars, though, before the lead was
poured in, they might all be supposed to have the same degree of heat or
coldness, as they had been exposed in the same room to the same air. You
will likewise observe, that the leaden bar, as it has cooled the melted
lead more than the wooden bars have done, so it is itself more heated by
the melted lead. There is a certain quantity of this fluid, called fire,
in every living human body; which fluid being in due proportion, keeps
the parts of the flesh and blood at such a just distance from each
other, as that the flesh and nerves are supple, and the blood fit for
circulation. If part of this due proportion of fire be conducted away,
by means of a contact with other bodies, as air, water, or metals, the
parts of our skin and flesh that come into such contact first draw more
near together than is agreeable, and give that sensation which we call
cold; and if too much be conveyed away, the body stiffens, the blood
ceases to flow, and death ensues. On the other hand, if too much of this
fluid be communicated to the flesh, the parts are separated too far, and
pain ensues, as when they are separated by a pin or lancet. The
sensation that the separation by fire occasions we call heat or burning.
My desk on which I now write, and the lock of my desk, are both exposed
to the same temperature of the air, and have, therefore, the same degree
of heat or cold: yet if I lay my hand successively on the wood and on
the metal, the latter feels much the coldest; not that it is really so,
but, being a better conductor, it more readily than the wood takes away
and draws into itself the fire that was in my skin. Accordingly, if I
lay one hand part on the lock and part on the wood, and after it had
laid on some time, I feel both parts with my other hand, I find the part
that has been in contact with the lock very sensibly colder to the touch
than the part that lay on the wood. How a living animal obtains its
quantity of this fluid, called fire, is a curious question. I have shown
that some bodies (as metals) have a power of attracting it stronger than
others; and I have sometimes suspected that a living body had some power
of attracting out of the air, or other bodies, the heat it wanted. Thus
metals hammered, or repeatedly bent, grow hot in the bent or hammered
part. But when I consider that air, in contact with the body, cools it;
that the surrounding air is rather heated by its contact with the body;
that every breath of cooler air drawn in carries off part of the body's
heat when it passes out again; that, therefore, there must be in the
body a fund for producing it, or otherwise the animal would soon grow
cold; I have been rather inclined to think that the fluid _fire_, as
well as the fluid _air_, is attracted by plants in their growth, and
becomes consolidated with the other materials of which they are formed,
and makes a great part of their substance; that, when they come to be
digested, and to suffer in the vessels a kind of fermentation, part of
the fire, as well as part of the air, recovers its fluid, active state
again, and diffuses itself in the body, digesting and separating it;
that the fire, so reproduced by digestion and separation, continually
leaving the body, its place is supplied by fresh quantities, arising
from the continual separation; that whatever quickens the motion of the
fluids in an animal quickens the separation, and reproduces more of the
fire, as exercise; that all the fire emitted by wood and other
combustibles, when burning, existed in them before in a solid state,
being only discovered when separating; that some fossils, as sulphur,
seacoal, &c., contain a great deal of solid fire; and that, in short,
what escapes and is dissipated in the burning of bodies, besides water
and earth, is generally the air and fire that before made parts of the
solid. Thus I imagine that animal heat arises by or from a kind of
fermentation in the juices of the body, in the same manner as heat
arises in the liquors preparing for distillation, wherein there is a
separation of the spirituous from the watery and earthy parts. And it is
remarkable, that the liquor in a distiller's vat, when in its best and
highest state of fermentation, as I have been informed, has the same
degree of heat with the human body: that is, about 94 or 96.
Thus, as by a constant supply of fuel in a chimney you keep a warm room,
so by a constant supply of food in the stomach you keep a warm body;
only where little exercise is used the heat may possibly be conducted
away too fast; in which case such materials are to be used for clothing
and bedding, against the effects of an immediate contact of the air, as
are in themselves bad conductors of heat, and, consequently, prevent its
being communicated through their substance to the air. Hence what is
called _warmth_ in wool, and its preference on that account to linen,
wool not being so good a conductor; and hence all the natural coverings
of animals to keep them warm are such as retain and confine the natural
heat in the body by being bad conductors, such as wool, hair, feathers,
and the silk by which the silkworm, in its tender embryo state, is first
clothed. Clothing, thus considered, does not make a man warm by _giving_
warmth, but by _preventing_ the too quick dissipation of the heat
produced in his body, and so occasioning an accumulation.
There is another curious question I will just venture to touch upon,
viz., Whence arises the sudden extraordinary degree of cold,
perceptible on mixing some chymical liquors, and even on mixing salt and
snow, where the composition appears colder than the coldest of the
ingredients? I have never seen the chymical mixtures made, but salt and
snow I have often mixed myself, and am fully satisfied that the
composition feels much colder to the touch, and lowers the mercury in
the thermometer more than either ingredient would do separately. I
suppose, with others, that cold is nothing more than the absence of heat
or fire. Now if the quantity of fire before contained or diffused in the
snow and salt was expelled in the uniting of the two matters, it must be
driven away either through the air or the vessel containing them. If it
is driven off through the air, it must warm the air, and a thermometer
held over the mixture, without touching it, would discover the heat by
the raising of the mercury, as it must and always does in warm air.
This, indeed, I have not tried, but I should guess it would rather be
driven off through the vessel, especially if the vessel be metal, as
being a better conductor than air; and so one should find the basin
warmer after such mixture. But, on the contrary, the vessel grows cold,
and even water, in which the vessel is sometimes placed for the
experiment, freezes into hard ice on the basin. Now I know not how to
account for this, otherwise than by supposing that the composition is a
better conductor of fire than the ingredients separately, and, like the
lock compared with the wood, has a stronger power of attracting fire,
and does accordingly attract it suddenly from the fingers, or a
thermometer put into it, from the basin that contains it, and from the
water in contact with the outside of the basin; so that the fingers have
the sensation of extreme cold by being deprived of much of their natural
fire; the thermometer sinks by having part of its fire drawn out of the
mercury; the basin grows colder to the touch, as, by having its fire
drawn into the mixture, it is become more capable of drawing and
receiving it from the hand; and, through the basin, the water loses its
fire that kept it fluid; so it becomes ice. One would expect that, from
all this attracted acquisition of fire to the composition, it should
become warmer; and, in fact, the snow and salt dissolve at the same time
into water, without freezing.
B. FRANKLIN.
* * * * *
_Peter Franklin, Newport, Rhode Island._
ON THE SALTNESS OF SEAWATER.
London, May 7, 1760.
* * It has, indeed, as you observe, been the opinion of some very great
naturalists, that the sea is salt only from the dissolution of mineral
or rock-salt which its waters happen to meet with. But this opinion
takes it for granted that all water was originally fresh, of which we
can have no proof. I own I am inclined to a different opinion, and
rather think all the water on this globe was originally salt, and that
the fresh water we find in springs and rivers is the produce of
distillation. The sun raises the vapours from the sea, which form
clouds, and fall in rain upon the land, and springs and rivers are
formed of that rain. As to the rock-salt found in mines, I conceive
that, instead of communicating its saltness to the sea, it is itself
drawn from the sea, and that, of course, the sea is now fresher than it
was originally. This is only another effect of nature's distillery, and
might be performed various ways.
It is evident, from the quantities of seashells, and the bones and teeth
of fishes found in high lands, that the sea has formerly covered them.
Then either the sea has been higher than it now is, and has fallen away
from those high lands, or they have been lower than they are, and were
lifted up out of the water to their present height by some internal
mighty force, such as we still feel some remains of when whole
continents are moved by earthquakes In either case it may be supposed
that large hollows, or valleys among hills, might be left filled with
seawater, which, evaporating, and the fluid part drying away in a course
of years, would leave the salt covering the bottom; and that salt,
coming afterward to be covered with earth from the neighbouring hills,
could only be found by digging through that earth. Or, as we know from
their effects that there are deep, fiery caverns under the earth, and
even under the sea, if at any time the sea leaks into any of them, the
fluid parts of the water must evaporate from that heat, and pass off
through some volcano, while the salt remains, and, by degrees and
continual accretion, becomes a great mass. Thus the cavern may at length
be filled, and the volcano connected with it cease burning, as many, it
is said, have done; and future miners, penetrating such cavern, find
what we call a salt-mine. This is a fancy I had on visiting the
salt-mines at Northwich with my son. I send you a piece of the rock-salt
which he brought up with him out of the mine.
B. FRANKLIN.
* * * * *
_To Miss Stephenson._
SALT WATER RENDERED FRESH BY DISTILLATION.--METHOD OF RELIEVING THIRST
BY SEAWATER.
Craven-street, August 10, 1761.
We are to set out this week for Holland, where we may possibly spend a
month, but purpose to be at home again before the coronation. I could
not go without taking leave of you by a line at least when I am so many
letters in your debt.
In yours of May 19, which I have before me, you speak of the ease with
which salt water may be made fresh by distillation, supposing it to be,
as I had said, that in evaporation the air would take up water, but not
the salt that was mixed with it. It is true that distilled seawater will
not be salt, but there are other disagreeable qualities that rise with
the water, in distillation; which, indeed, several besides Dr. Hales
have endeavoured by some means to prevent, but as yet their methods have
not been brought much into use.
I have a singular opinion on this subject, which I will venture to
communicate to you, though I doubt you will rank it among my whims. It
is certain that the skin has _imbibing_ as well as _discharging_ pores;
witness the effects of a blistering-plaster, &c. I have read that a man,
hired by a physician to stand, by way of experiment, in the open air
naked during a moist night, weighed near three pounds heavier in the
morning. I have often observed myself, that however thirsty I may have
been before going into the water to swim, I am never long so in the
water. These imbibing pores, however, are very fine; perhaps fine
enough, in filtering, to separate salt from water; for though I have
soaked (by swimming, when a boy) several hours in the day, for several
days successively, in salt water, I never found my blood and juices
salted by that means, so as to make me thirsty or feel a salt taste in
my mouth; and it is remarkable that the flesh of seafish, though bred in
salt water, is not salt. Hence I imagined that if people at sea,
distressed by thirst, when their fresh water is unfortunately spent,
would make bathing-tubs of their empty water-casks, and, filling them
with seawater, sit in them an hour or two each day, they might be
greatly relieved. Perhaps keeping their clothes constantly wet might
have an almost equal effect; and this without danger of catching cold.
Men do not catch cold by wet clothes at sea. Damp, but not wet linen,
may possibly give colds; but no one catches cold by bathing, and no
clothes can be wetter than water itself. Why damp clothes should then
occasion colds, is a curious question, the discussion of which I reserve
for a future letter or some future conversation.