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The
WORKS
Of
BENJAMIN FRANKLIN, L.L.D.
VOL. 2.
[Illustration: (W & G Cooke Sculptor.)]
PRINTED,
for Longman, Hurst, Rees, & Orme, Paternoster Row, London.
THE
COMPLETE
WORKS,
IN
PHILOSOPHY, POLITICS, AND MORALS,
OF THE LATE
DR. BENJAMIN FRANKLIN,
NOW FIRST COLLECTED AND ARRANGED:
WITH
MEMOIRS OF HIS EARLY LIFE,
WRITTEN BY HIMSELF.
IN THREE VOLUMES.
VOL. II.
London:
PRINTED FOR J. JOHNSON, ST. PAUL'S CHURCH-YARD;
AND LONGMAN, HURST, REES AND ORME,
PATERNOSTER-ROW.
1806.
J. CUNDEE, PRINTER
LONDON
CONTENTS.
VOL. II.
LETTERS AND PAPERS ON PHILOSOPHICAL SUBJECTS.
Physical and meteorological observations, conjectures and
suppositions 1
On water-spouts 11
The same subject continued 13
Water-spouts and whirlwinds compared 19
Description of a water-spout at Antigua 34
Shooting stars 36
Water-spouts and whirlwinds 37
Observations on the meteorological paper; by a gentleman in
Connecticut 45
Observations in answer to the foregoing, by B. Franklin 49
Observations on the meteorological paper; sent by a gentleman in
New York to B. Franklin 51
Answer to the foregoing observations, by B. Franklin 55
Gentleman of New York in reply 58
Account of a whirlwind at Maryland 61
On the north east storms in North America 63
Meteorological imaginations and conjectures 66
Suppositions and conjectures towards forming an hypothesis, for
the explanation of the aurora borealis 69
On cold produced by evaporation 75
On the same subject 83
Concerning the light in sea-water 88
On the saltness of sea-water 91
On the effect of air on the barometer, and the benefits derived
from the study of insects 92
On the Bristol waters, and the tide in rivers 95
On the same subject 102
Salt-water rendered fresh by distillation.--Method of relieving
thirst by sea-water 103
Tendency of rivers to the sea.--Effect of the sun's rays on cloth
of different colours 105
On the vis inertiæ of matter 110
On the different strata of the earth 116
On the theory of the earth 117
New and curious theory of light and heat 122
Queries and conjectures relating to magnetism and the theory of
the earth 125
On the nature of sea coal 125
Effect of vegetation on noxious air 129
On the inflammability of the surface of certain rivers in America 130
On the different quantities of rain which fall at different
heights over the same ground 133
Slowly sensible hygrometer proposed, for certain purposes 135
Curious instance of the effect of oil on water 142
Letters on the stilling of waves by means of oil 144
Extract of a letter from Mr. Tengnagel to Count Bentinck, dated at
Batavia, the 5th of January, 1770 154
On the difference of navigation in shoal and deep water 158
Sundry maritime observations 162
Remarks upon the navigation from Newfoundland to New-York, in
order to avoid the Gulph Stream on one hand, and on the other
the shoals that lie to the southward of Nantucket and of St.
George's Banks 197
Observations of the warmth of the sea-water, &c. by Fahrenheit's
Thermometer, in crossing the Gulph Stream; with other remarks
made on board the Pensylvania packet, Capt. Osborne, bound
from London to Philadelphia, in April and May, 1775 199
Observations of the warmth of the sea-water, &c. by Fahrenheit's
thermometer; with other remarks made on board the Reprisal,
Capt. Wycks, bound from Philadelphia to France, in October
and November, 1776 200
A journal of a voyage from the Channel between France and England
towards America 202
On the art of swimming 206
On the same subject, in answer to some enquiries of M. Dubourg 210
On the free use of air 213
On the causes of colds 214
Dr. Stark, and Dr. Letsom 215
Number of deaths in Philadelphia by inoculation ibid
Answer to the preceding 217
On the effects of lead upon the human constitution 219
Observations on the prevailing doctrines of life and death 222
An account of the new-invented Pensylvanian fire-places 225
On the causes and cure of smoky chimneys 256
Description of a new stove for burning of pitcoal, and consuming
all its smoke 296
Method of contracting chimneys.--Modesty in disputation 317
Covering houses with copper 318
On the same subject 320
Paper referred to in the preceding letter 322
Magical square of squares 324
Magical circle 328
New musical instrument composed of glasses 330
Best mediums for conveying sound 335
On the harmony and melody of the old Scotch tunes 338
On the defects of modern music 343
Description of the process to be observed in making large sheets
of paper in the Chinese manner, with one smooth surface 349
On modern innovations in the English language and in printing 351
A scheme for a new alphabet and reformed mode of spelling; with
remarks and examples concerning the same; and an enquiry into
its uses, in a correspondence between Miss S---- and Dr. Franklin,
written in the characters of the alphabet 357
Rules for a club formerly established in Philadelphia 366
Questions discussed by the Junto forming the preceding club 369
Sketch of an English school; for the consideration of the trustees
of the Philadelphia Academy 370
Advice to youth in reading 378
PAPERS ON SUBJECTS OF GENERAL POLITICS.
Observations concerning the increase of mankind, peopling of
countries, &c 383
Remarks on some of the foregoing observations, showing particularly
the effect which manners have on population 392
Plan by Messieurs Franklin and Dalrymple, for benefiting distant
unprovided countries 403
Concerning the provision made in China against famine 407
Positions to be examined, concerning national wealth 408
Political fragments, supposed either to be written by Dr. Franklin,
or to contain sentiments nearly allied to his own 411
On the price of corn, and management of the poor 418
On luxury, idleness, and industry 424
On smuggling, and its various species 430
Observations on war 435
Notes copied from Dr. Franklin's writing in pencil in the margin of
Judge Foster's celebrated argument in favour of the impressing
of seamen 437
On the criminal laws, and the practice of privateering 441
A parable against persecution, in imitation of scripture language 450
A letter concerning persecution in former ages, the maintenance of
the clergy, American bishops, and the state of toleration in Old
England and New England compared 452
On the slave trade 459
Account of the highest court of judicature in Pensylvania, viz.
The court of the press 463
LIST OF THE PLATES
PLATE V. Water-Spouts facing page 16
PLATE VI. Maritime Observations 163
PLATE VII. A Chart of the Gulph Stream 197
PLATE VIII. Pensylvania Fire-Place 235
PLATE VIII*. Profile of the Pensylvania Chimnie 238
PLATE IX. Remedies for Smoky Chimnies 269
PLATE X. Stove for Burning Pit-Coal 297
PLATE XI. A Magic Square of Squares 327
PLATE XII. A Magic Circle of Circles 328
_ERRATA._
_Page._ _Line._
117 penult. for preceding day, read the preceding day.
254 17: for the annexed cut, read Plate VIII.
276 11: for Plate I, read Plate IX.
293 23: for Fig. 13, read Fig. 10.
318 9: for descent, read decent.
326 5: for Plate XI, read Plate V. Fig. 3.
LETTERS AND PAPERS
ON
_PHILOSOPHICAL SUBJECTS._
_LETTERS AND PAPERS_
ON
PHILOSOPHICAL SUBJECTS.
_Physical and Meteorological Observations, Conjectures and
Suppositions._
Read at the Royal Society, June 3, 1756.
The particles of air are kept at a distance from each other by their
mutual repulsion.
Every three particles, mutually and equally repelling each other,
must form an equilateral triangle.
All the particles of air gravitate towards the earth, which
gravitation compresses them, and shortens the sides of the triangles,
otherwise their mutual repellency would force them to greater
distances from each other.
Whatever particles of other matter (not endued with that repellency)
are supported in air, must adhere to the particles of air, and be
supported by them; for in the vacancies there is nothing they can
rest on.
Air and water mutually attract each other. Hence water will dissolve
in air, as salt in water.
The specific gravity of matter is not altered by dividing the
matter, though the superficies be increased. Sixteen leaden bullets,
of an ounce each, weigh as much in water as one of a pound, whose
superficies is less.
Therefore the supporting of salt in water is not owing to its
superficies being increased.
A lump of salt, though laid at rest at the bottom of a vessel of
water, will dissolve therein, and its parts move every way, till
equally diffused in the water; therefore there is a mutual attraction
between water and salt. Every particle of water assumes as many of
salt as can adhere to it; when more is added, it precipitates, and
will not remain suspended.
Water, in the same manner, will dissolve in air, every particle of
air assuming one or more particles of water. When too much is added,
it precipitates in rain.
But there not being the same contiguity between the particles of air
as of water, the solution of water in air is not carried on without a
motion of the air, so as to cause a fresh accession of dry particles.
Part of a fluid, having more of what it dissolves, will communicate
to other parts that have less. Thus very salt water, coming in
contact with fresh, communicates its saltness till all is equal, and
the sooner if there is a little motion of the water.
Even earth will dissolve, or mix with air. A stroke of a horse's hoof
on the ground, in a hot dusty road, will raise a cloud of dust, that
shall, if there be a light breeze, expand every way, till, perhaps,
near as big as a common house. It is not by mechanical motion
communicated to the particles of dust by the hoof, that they fly so
far, nor by the wind, that they spread so wide: but the air near
the ground, more heated by the hot dust struck into it, is rarefied
and rises, and in rising mixes with the cooler air, and communicates
of its dust to it, and it is at length so diffused as to become
invisible. Quantities of dust are thus carried up in dry seasons:
showers wash it from the air, and bring it down again. For water
attracting it stronger, it quits the air, and adheres to the water.
Air, suffering continual changes in the degrees of its heat, from
various causes and circumstances, and, consequently, changes in its
specific gravity, must therefore be in continual motion.
A small quantity of fire mixed with water (or degree of heat therein)
so weakens the cohesion of its particles, that those on the surface
easily quit it, and adhere to the particles of air.
A greater degree of heat is required to break the cohesion between
water and air.
Air moderately heated will support a greater quantity of water
invisibly than cold air; for its particles being by heat repelled
to a greater distance from each other, thereby more easily keep
the particles of water that are annexed to them from running into
cohesions that would obstruct, refract, or reflect the light.
Hence when we breathe in warm air, though the same quantity of
moisture may be taken up from the lungs, as when we breathe in cold
air, yet that moisture is not so visible.
Water being extremely heated, _i.e._ to the degree of boiling, its
particles in quitting it so repel each other, as to take up vastly
more space than before, and by that repellency support themselves,
expelling the air from the space they occupy. That degree of
heat being lessened, they again mutually attract, and having no
air-particles mixed to adhere to, by which they might be supported
and kept at a distance, they instantly fall, coalesce, and become
water again.
The water commonly diffused in our atmosphere never receives such
a degree of heat from the sun, or other cause, as water has when
boiling; it is not, therefore, supported by such heat, but by
adhering to air.
Water being dissolved in, and adhering to air, that air will not
readily take up oil, because of the mutual repellency between water
and oil.
Hence cold oils evaporate but slowly, the air having generally a
quantity of dissolved water.
Oil being heated extremely, the air that approaches its surface will
be also heated extremely; the water then quitting it, it will attract
and carry off oil, which can now adhere to it. Hence the quick
evaporation of oil heated to a great degree.
Oil being dissolved in air, the particles to which it adheres will
not take up water.
Hence the suffocating nature of air impregnated with burnt grease, as
from snuffs of candles and the like. A certain quantity of moisture
should be every moment discharged and taken away from the lungs; air
that has been frequently breathed, is already overloaded, and, for
that reason, can take no more, so will not answer the end. Greasy
air refuses to touch it. In both cases suffocation for want of the
discharge.
Air will attract and support many other substances.
A particle of air loaded with adhering water, or any other matter, is
heavier than before and would descend.
The atmosphere supposed at rest, a loaded descending particle must
act with a force on the particles it passes between, or meets with,
sufficient to overcome, in some degree, their mutual repellency, and
push them nearer to each other.
[Illustration: (of air particles interacting)
A
O O O
F B C G
O O O O
O O O
D
O O O O
E
]
Thus, supposing the particles A B C D, and the other near them, to
be at the distance caused by their mutual repellency (confined by
their common gravity) if A would descend to E, it must pass between B
and C; when it comes between B and C, it will be nearer to them than
before, and must either have pushed them nearer to F and G, contrary
to their mutual repellency, or pass through by a force exceeding
its repellency with them. It then approaches D, and, to move it out
of the way, must act on it with a force sufficient to overcome its
repellency with the two next lower particles, by which it is kept in
its present situation.
Every particle of air, therefore, will bear any load inferior to the
force of these repulsions.
Hence the support of fogs, mists, clouds.
Very warm air, clear, though supporting a very great quantity of
moisture, will grow turbid and cloudy on the mixture of a colder air,
as foggy turbid air will grow clear by warming.
Thus the sun shining on a morning fog, dissipates it; clouds are seen
to waste in a sun-shiny day.
But cold condenses and renders visible the vapour; a tankard or
decanter filled with cold water will condense the moisture of warm
clear air on its outside, where it becomes visible as dew, coalesces
into drops, descends in little streams.
The sun heats the air of our atmosphere most near the surface of
the earth; for there, besides the direct rays, there are many
reflections. Moreover, the earth itself being heated, communicates of
its heat to the neighbouring air.
The higher regions, having only the direct rays of the sun passing
through them, are comparatively very cold. Hence the cold air on the
tops of mountains, and snow on some of them all the year, even in the
torrid zone. Hence hail in summer.
If the atmosphere were, all of it (both above and below) always of
the same temper as to cold or heat, then the upper air would always
be _rarer_ than the lower, because the pressure on it is less;
consequently lighter, and therefore would keep its place.
But the upper air may be more condensed by cold, than the lower air
by pressure; the lower more expanded by heat, than the upper for want
of pressure. In such case the upper air will become the heavier, the
lower the lighter.
The lower region of air being heated and expanded heaves up, and
supports for some time the colder heavier air above, and will
continue to support it while the equilibrium is kept. Thus water
is supported in an inverted open glass, while the equilibrium is
maintained by the equal pressure upwards of the air below; but the
equilibrium by any means breaking, the water descends on the heavier
side, and the air rises into its place.
The lifted heavy cold air over a heated country, becoming by any
means unequally supported, or unequal in its weight, the heaviest
part descends first, and the rest follows impetuously. Hence gusts
after heats, and hurricanes in hot climates. Hence the air of gusts
and hurricanes cold, though in hot climes and seasons; it coming from
above.
The cold air descending from above, as it penetrates our warm region
full of watry particles, condenses them, renders them visible,
forms a cloud thick and dark, overcasting sometimes, at once, large
and extensive; sometimes, when seen at a distance, small at first,
gradually increasing; the cold edge, or surface of the cloud,
condensing the vapours next it, which form smaller clouds that join
it, increase its bulk, it descends with the wind and its acquired
weight, draws nearer the earth, grows denser with continual additions
of water, and discharges heavy showers.
Small black clouds thus appearing in a clear sky, in hot climates,
portend storms, and warn seamen to hand their sails.
The earth, turning on its axis in about twenty-four hours, the
equatorial parts must move about fifteen miles in each minute; in
northern and southern latitudes this motion is gradually less to the
poles, and there nothing.
If there was a general calm over the face of the globe, it must be by
the air's moving in every part as fast as the earth or sea it covers.
He that sails, or rides, has insensibly the same degree of motion as
the ship or coach with which he is connected. If the ship strikes
the shore, or the coach stops suddenly, the motion continuing in the
man, he is thrown forward. If a man were to jump from the land into
a swift sailing ship, he would be thrown backward (or towards the
stern) not having at first the motion of the ship.
He that travels by sea or land, towards the equinoctial, gradually
acquires motion; from it, loses.
But if a man were taken up from latitude 40 (where suppose the
earth's surface to move twelve miles per minute) and immediately set
down at the equinoctial, without changing the motion he had, his
heels would be struck up, he would fall westward. If taken up from
the equinoctial, and set down in latitude 40, he would fall eastward.
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 earth and air 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[1].
Thus, when we ride in a calm, it seems a wind against us: if we ride
with the wind, and faster, even that will seem a small wind against
us.
The air rarefied between the tropics, and rising, must flow in the
higher region north and south. Before it rose, it had acquired the
greatest motion the earth's rotation could give it. It retains some
degree of this motion, and descending in higher latitudes, where the
earth's motion is less, will appear a westerly wind, yet tending
towards the equatorial parts, to supply the vacancy occasioned by
the air of the lower regions flowing thitherwards.
Hence our general cold winds are about north west, our summer cold
gusts the same.
The air in sultry weather, though not cloudy, has a kind of haziness
in it, which makes objects at a distance appear dull and indistinct.
This haziness is occasioned by the great quantity of moisture equally
diffused in that air. When, by the cold wind blowing down among it,
it is condensed into clouds, and falls in rain, the air becomes purer
and clearer. Hence, after gusts, distant objects appear distinct,
their figures sharply terminated.
Extreme cold winds congeal the surface of the earth, by carrying off
its fire. Warm winds afterwards blowing over that frozen surface will
be chilled by it. Could that frozen surface be turned under, and
a warmer turned up from beneath it, those warm winds would not be
chilled so much.
The surface of the earth is also sometimes much heated by the sun:
and such heated surface not being changed heats the air that moves
over it.
Seas, lakes, and great bodies of water, agitated by the winds,
continually change surfaces; the cold surface in winter is turned
under by the rolling of the waves, and a warmer turned up; in summer,
the warm is turned under, and colder turned up. Hence the more equal
temper of sea-water, and the air over it. Hence, in winter, winds
from the sea seem warm, winds from the land cold. In summer the
contrary.
Therefore the lakes north-west of us[2], as they are
not so much frozen, nor so apt to freeze as the earth, rather
moderate than increase the coldness of our winter winds.
The air over the sea being warmer, and therefore lighter in winter
than the air over the frozen land, may be another cause of our
general N. W. winds, which blow off to sea at right angles from our
North-American coast. The warm light sea air rising, the heavy cold
land air pressing into its place.
Heavy fluids descending, frequently form eddies, or whirlpools, as
is seen in a funnel, where the water acquires a circular motion,
receding every way from a centre, and leaving a vacancy in the
middle, greatest above, and lessening downwards, like a speaking
trumpet, its big end upwards.
Air descending, or ascending, may form the same kind of eddies,
or whirlings, the parts of air acquiring a circular motion, and
receding from the middle of the circle by a centrifugal force, and
leaving there a vacancy; if descending, greatest above, and lessening
downwards; if ascending, greatest below, and lessening upwards; like
a speaking trumpet, standing its big end on the ground.
When the air descends with violence in some places, it may rise with
equal violence in others, and form both kinds of whirlwinds.
The air in its whirling motion receding every way from the centre or
axis of the trumpet leaves there a vacuum, which cannot be filled
through the sides, the whirling air, as an arch, preventing; it must
then press in at the open ends.
The greatest pressure inwards must be at the lower end, the greatest
weight of the surrounding atmosphere being there. The air entering
rises within, and carries up dust, leaves, and even heavier bodies
that happen in its way, as the eddy, or whirl, passes over land.
If it passes over water, the weight of the surrounding atmosphere
forces up the water into the vacuity, part of which, by degrees,
joins with the whirling air, and adding weight, and receiving
accelerated motion, recedes still farther from the centre or axis of
the trump, as the pressure lessens; and at last, as the trump widens,
is broken into small particles, and so united with air as to be
supported by it, and become black clouds at the top of the trump.
Thus these eddies may be whirlwinds at land, water-spouts at sea. A
body of water so raised, may be suddenly let fall, when the motion,
&c. has not strength to support it, or the whirling arch is broken so
as to admit the air: falling in the sea, it is harmless, unless ships
happen under it; but if in the progressive motion of the whirl it has
moved from the sea, over the land, and then breaks, sudden, violent,
and mischievous torrents are the consequences.
B. FRANKLIN.
FOOTNOTES:
[1] See a paper on this subject, by the late ingenious Mr. Hadley,
in the Philosophical Transactions, wherein this hypothesis for
explaining the trade-winds first appeared.
[2] In Pensylvania.
DOCTOR ----[3] OF BOSTON, TO BENJAMIN FRANKLIN, ESQ. AT PHILADELPHIA.
_On Water-Spouts._
Read at the Royal Society, June 3, 1756.
_Boston, October 16, 1752_.
SIR,
I find by a word or two in your last[4], that you are willing to
be found fault with; which authorises me to let you know what I
am at a loss about in your papers, which is only in the article
of the water-spout. I am in doubt, whether water in bulk, or even
broken into drops, ever ascends into the region of the clouds _per
vorticem_; i. e. whether there be, in reality, what I call a direct
water-spout. I make no doubt of direct and inverted whirl-winds; your
description of them, and the reason of the thing, are sufficient.
I am sensible too, that they are very strong, and often move
considerable weights. But I have not met with any historical accounts
that seem exact enough to remove my scruples concerning the ascent
abovesaid.
Descending spouts (as I take them to be) are many times seen, as I
take it, in the calms, between the sea and land trade-winds on the
coast of Africa. These contrary winds, or diverging, I can conceive
may occasion them, as it were by suction, making a breach in a large
cloud. But I imagine they have, at the same time, a tendency to
hinder any direct or rising spout, by carrying off the lower part of
the atmosphere as fast as it begins to rarefy; and yet spouts are
frequent here, which strengthens my opinion, that all of them descend.
But however this be, I cannot conceive a force producible by the
rarefication and condensation of our atmosphere, in the circumstances
of our globe, capable of carrying water, in large portions, into the
region of the clouds. Supposing it to be raised, it would be too
heavy to continue the ascent beyond a considerable height, unless
parted into small drops; and even then, by its centrifugal force,
from the manner of conveyance, it would be flung out of the circle,
and fall scattered, like rain.
But I need not expatiate on these matters to you. I have mentioned
my objections, and, as truth is my pursuit, shall be glad to be
informed. I have seen few accounts of these whirl or eddy winds, and
as little of the spouts; and these, especially, lame and poor things
to obtain any certainty by. If you know any thing determinate that
has been observed, I shall hope to hear from you; as also of any
mistake in my thoughts. I have nothing to object to any other part
of your suppositions: and as to that of the trade-winds, I believe
nobody can.
I am, &c.
_P. S._. The figures in the _Philosophical Transactions_ show, by
several circumstances, that they all descended, though the relators
seemed to think they took up water.
FOOTNOTES:
[3] Dr. Perkins. _Editor._
[4] A Letter on Inoculation, which is transferred to a subsequent
part of this volume, that the papers on meteorological subjects may
not be interrupted. _Editor._
DR. PERKINS OF BOSTON, TO BENJAMIN FRANKLIN, ESQ. AT PHILADELPHIA.
_The same Subject continued._
Read at the Royal Society, June 24, 1756.
_Boston, October 23, 1752._
SIR,
In the inclosed, you have all I have to say of that matter[5]. It
proved longer than I expected, so that I was forced to add a cover to
it. I confess it looks like a dispute; but that is quite contrary to
my intentions.
The sincerity of friendship and esteem were my motives; nor do I
doubt your scrupling the goodness of the intention. However, I must
confess I cannot tell exactly how far I was acted by hopes of better
information, in discovering the whole foundation of my opinion,
which, indeed, is but an opinion, as I am very much at a loss about
the validity of the reasons. I have not been able to differ from you
in sentiment concerning any thing else in your _Suppositions_. In the
present case I lie open to conviction, and shall be the gainer when
informed. If I am right, you will know that, without my adding any
more. Too much said on a merely speculative matter, is but a robbery
committed on practical knowledge. Perhaps I am too much pleased with
these dry notions: however, by this you will see that I think it
unreasonable to give you more trouble about them, than your leisure
and inclination may prompt you to.
I am, &c.
Since my last I considered, that, as I had begun with the reasons of
my dissatisfaction about the ascent of water in spouts, you would not
be unwilling to hear the whole I have to say, and then you will know
what I rely upon.
What occasioned my thinking all spouts descend, is, that I found some
did certainly do so. A difficulty appeared concerning the ascent of
so heavy a body as water, by any force I was apprised of, as probably
sufficient. And, above all, a view of Mr. Stuart's portraits of
spouts, in the _Philosophical Transactions_.
Some observations on these last will include the chief part of my
difficulties. Mr. Stuart has given us the figures of a number
observed by him in the Mediterranean: all with some particulars which
make for my opinion, if well drawn.
The great spattering, which relators mention in the water where the
spout descends, and which appears in all his draughts, I conceive to
be occasioned by drops descending very thick and large into the place.
On the place of this spattering, arises the appearance of a bush,
into the centre of which the spout comes down. This bush I take to
be formed by a spray, made by the force of these drops, which being
uncommonly large, and descending with unusual force by a stream of
wind descending from the cloud with them, increases the height of
the spray: which wind being repulsed by the surface of the waters
rebounds and spreads; by the first raising the spray higher than it
otherwise would go; and by the last making the top of the bush appear
to bend outwards (_i. e._) the cloud of spray is forced off from the
trunk of the spout, and falls backward.
The bush does the same where there is no appearance of a spout
reaching it; and is depressed in the middle, where the spout is
expected. This, I imagine, to be from numerous drops of the spout
falling into it, together with the wind I mentioned, by their
descent, which beat back the rising spray in the centre.
This circumstance, of the bush bending outwards at the top, seems not
to agree with what I call a direct whirlwind, but consistent with the
reversed; for a direct one would sweep the bush inwards; if, in that
case, any thing of a bush would appear.
The pillar of water, as they call it, from its likeness, I suppose
to be only the end of the spout immersed in the bush, a little
blackened by the additional cloud, and, perhaps, appears to the eye
beyond its real bigness, by a refraction in the bush, and which
refraction may be the cause of the appearance of separation, betwixt
the part in the bush, and that above it. The part in the bush is
cylindrical, as it is above (_i. e._) the bigness the same from the
top of the bush to the water. Instead of this shape, in case of a
whirlwind, it must have been pyramidical.
Another thing remarkable, is, the curve in some of them: this is
easy to conceive, in case of descending parcels of drops through
various winds, at least till the cloud condenses so fast as to come
down, as it were, _uno rivo_. But it is harder to me to conceive it
in the ascent of water, that it should be conveyed along, secure of
not leaking or often dropping through the under side, in the prone
part: and, should the water be conveyed so swiftly, and with such
force, up into the cloud, as to prevent this, it would, by a natural
disposition to move on in a present direction, presently straiten the
curve, raising the shoulder very swiftly, till lost in the cloud.
Over every one of Stuart's figures, I see a cloud: I suppose his
clouds were first, and then the spout; I do not know whether it be so
with all spouts, but suppose it is. Now, if whirlwinds carried up the
water, I should expect them in fair weather, but not under a cloud;
as is observable of whirlwinds; they come in fair weather, not under
the shade of a cloud, nor in the night; since shade cools the air:
but, on the contrary, violent winds often descend from the clouds;
strong gusts which occupy small spaces; and from the higher regions,
extensive hurricanes, &c.
Another thing is the appearance of the spout _coming from_ the cloud.
This I cannot account for on the notion of a direct spout, but in the
real descending one, it is easy. I take it, that the cloud begins
first of all to pour out drops at that particular spot, or _foramen_;
and, when that current of drops increases, so as to force down wind
and vapour, the spout becomes so far as that goes opaque. I take it,
that no clouds drop spouts, but such as make very fast, and happen
to condense in a particular spot, which perhaps is coldest, and
gives a determination downwards, so as to make a passage through the
subjacent atmosphere.
If spouts ascend, it is to carry up the warm rarefied air below, to
let down all and any that is colder above; and, if so, they must
carry it through the cloud they go into (for that is cold and dense,
I imagine) perhaps far into the higher region, making a wonderful
appearance at a convenient distance to observe it, by the swift rise
of a body of vapour, above the region of the clouds. But as this has
never been observed in any age, if it be supposeable that is all.
I cannot learn by mariners, that any wind blows towards a spout more
than any other way; but it blows towards a whirlwind, for a large
distance round.
I suppose there has been no instance of the water of a spout being
salt, when coming across any vessel at sea. I suppose too, that there
have been no salt rains; these would make the case clear.
I suppose it is from some unhappy effects of these dangerous
creatures of nature, that sailors have an universal dread on them of
breaking in their decks, should they come across them. I imagine
spouts, in cold seasons, as Gordon's in the Downs, prove the descent.
_Query._ Whether there is not always more or less cloud, first, where
a spout appears?
Whether they are not, generally, on the borders of trade-winds; and
whether this is for, or against me?
Whether there be any credible account of a whirlwind's carrying up
all the water in a pool, or small pond: as when shoal, and the banks
low, a strong gust might be supposed to blow it all out?
Whether a violent tornado, of a small extent, and other sudden
and strong gusts, be not winds from above, descending nearly
perpendicular; and, whether many that are called whirlwinds at sea,
are any other than these; and so might be called air-spouts, if they
were objects of sight?
I overlooked, in its proper place, Stuart's No. 11, which is curious
for its inequalities, and, in particular, the approach to breaking,
which, if it would not be too tedious, I would have observed a little
upon, in my own way, as, I think, this would argue against the
ascent, &c. but I must pass it, not only for the reason mentioned,
but want of room besides.
As to Mr. Stuart's ocular demonstration of the ascent in his great
perpendicular spout, the only one it appears in, I say, as to this,
what I have written supposes him mistaken, which, yet, I am far from
asserting.
The force of an airy vortex, having less influence on the solid drops
of water, than on the interspersed cloudy vapours, makes the last
whirl round swifter, though it descend slower: and this might easily
deceive, without great care, the most unprejudiced person.
FOOTNOTE:
[5] Water-Spouts.
TO DOCTOR ----[6], OF BOSTON.
_Water-Spouts and Whirlwinds compared._
Read at the Royal Society, June 24, 1756.
_Philadelphia, Feb. 4, 1753._
SIR,
I ought to have written to you, long since, in answer to yours of
October 16, concerning the water-spout; but business partly, and
partly a desire of procuring further information, by enquiry among my
seafaring acquaintance, induced me to postpone writing, from time to
time, till I am now almost ashamed to resume the subject, not knowing
but you may have forgot what has been said upon it.
Nothing certainly, can be more improving to a searcher into nature,
than objections judiciously made to his opinion, taken up, perhaps,
too hastily: for such objections oblige him to re-study the
point, consider every circumstance carefully, compare facts, make
experiments, weigh arguments, and be slow in drawing conclusions.
And hence a sure advantage results; for he either confirms a truth,
before too slightly supported; or discovers an error, and receives
instruction from the objector.
In this view I consider the objections and remarks you sent me, and
thank you for them sincerely: but, how much soever my inclinations
lead me to philosophical enquiries, I am so engaged in business,
public and private, that those more pleasing pursuits are frequently
interrupted, and the chain of thought, necessary to be closely
continued in such disquisitions, is so broken and disjointed, that it
is with difficulty I satisfy myself in any of them: and I am now not
much nearer a conclusion, in this matter of the spout, than when I
first read your letter.
Yet, hoping we may, in time, sift out the truth between us, I will
send you my present thoughts, with some observations on your reasons
on the accounts in the _Transactions_, and on other relations I have
met with. Perhaps, while I am writing, some new light may strike me,
for I shall now be obliged to consider the subject with a little more
attention.
I agree with you, that, by means of a vacuum in a whirlwind, water
cannot be supposed to rise in large masses to the region of the
clouds; for the pressure of the surrounding atmosphere could not
force it up in a continued body, or column, to a much greater height,
than thirty feet. But, if there really is a vacuum in the centre, or
near the axis of whirlwinds, then, I think, water may rise in such
vacuum to that height, or to a less height, as the vacuum may be less
perfect.
I had not read Stuart's account, in the _Transactions_, for many
years, before the receipt of your letter, and had quite forgot it;
but now, on viewing his draughts, and considering his descriptions, I
think they seem to favour _my hypothesis_; for he describes and draws
columns of water, of various heights, terminating abruptly at the
top, exactly as water would do, when forced up by the pressure of the
atmosphere into an exhausted tube.
I must, however, no longer call it _my hypothesis_, since I find
Stuart had the same thought, though somewhat obscurely expressed,
where he says, "he imagines this phenomenon may be solved by suction
(improperly so called) or rather pulsion, as in the application of a
cupping glass to the flesh, the air being first voided by the kindled
flax." In my paper, I supposed a whirlwind and a spout to be the
same thing, and to proceed from the same cause; the only difference
between them being, that the one passes over land, the other over
water, I find, also, in the _Transactions_, that M. de la Pryme was
of the same opinion; for he there describes two spouts, as he calls
them, which were seen at different times, at Hatfield, in Yorkshire,
whose appearances in the air were the same with those of the spouts
at sea, and effects the same with those of real whirlwinds.
Whirlwinds have generally a progressive, as well as a circular
motion; so had what is called the spout, at Topsham--(_See the
account of it in the Transactions_) which also appears, by its
effects described, to have been a real whirlwind. Water-spouts have,
also, a progressive motion; this is sometimes greater, and sometimes
less; in some violent, in others barely perceivable. The whirlwind at
Warrington continued long in Acrement-Close.
Whirlwinds generally arise after calms and great heats: the same
is observed of water-spouts, which are, therefore, most frequent
in the warm latitudes. The spout that happened in cold weather, in
the Downs, described by Mr. Gordon in the _Transactions_, was, for
that reason, thought extraordinary; but he remarks withal, that the
weather, though cold when the spout appeared, was soon after much
colder; as we find it, commonly, less warm after a whirlwind.
You agree, that the wind blows every way towards a whirlwind,
from a large space round. An intelligent whaleman of Nantucket,
informed me that three of their vessels, which were out in search
of whales, happening to be becalmed, lay in sight of each other,
at about a league distance, if I remember right, nearly forming a
triangle: after some time, a water-spout appeared near the middle
of the triangle, when a brisk breeze of wind sprung up, and every
vessel made sail; and then it appeared to them all, by the setting
of the sails, and the course each vessel stood, that the spout was
to the leeward of every one of them; and they all declared it to
have been so, when they happened afterwards in company, and came to
confer about it. So that in this particular likewise, whirlwinds and
water-spouts agree.
But, if that which appears a water-spout at sea, does sometimes,
in its progressive motion, meet with and pass over land, and there
produce all the phenomena and effects of a whirlwind, it should
thence seem still more evident, that a whirlwind and a spout are the
same. I send you, herewith, a letter from an ingenious physician of
my acquaintance, which gives one instance of this, that fell within
his observation.
A fluid, moving from all points horizontally, towards a centre, must,
at that centre, either ascend or descend. Water being in a tub, if a
hole be opened in the middle of the bottom, will flow from all sides
to the centre, and there descend in a whirl. But, air flowing on and
near the surface of land or water, from all sides, towards a centre,
must, at that centre ascend; the land or water hindering its descent.
If these concentring currents of air be in the upper region, they
may, indeed, descend in the spout or whirlwind; but then, when the
united current reached the earth or water, it would spread, and,
probably, blow every way from the centre. There may be whirlwinds
of both kinds, but from the commonly observed effects, I suspect
the rising one to be the most common: when the upper air descends,
it is, perhaps, in a greater body, extending wider, as in our
thunder-gusts, and without much whirling; and, when air descends in a
spout, or whirlwind, I should rather expect it would press the roof
of a house _inwards_, or force _in_ the tiles, shingles, or thatch,
force a boat down into the water, or a piece of timber into the
earth, than that it would lift them up, and carry them away.
It has so happened, that I have not met with any accounts of spouts,
that certainly descended; I suspect they are not frequent. Please to
communicate those you mention. The apparent dropping of a pipe from
the clouds towards the earth or sea, I will endeavour to explain
hereafter.
The augmentation of the cloud, which, as I am informed, is generally,
if not always the case, during a spout, seems to shew an ascent,
rather than a descent of the matter of which such cloud is composed;
for a descending spout, one would expect, should diminish a cloud.
I own, however, that cold air descending, may, by condensing the
vapours in a lower region, form and increase clouds; which, I think,
is generally the case in our common thunder-gusts, and, therefore, do
not lay great stress on this argument.
Whirlwinds and spouts, are not always, though most commonly, in
the day time. The terrible whirlwind which damaged a great part of
Rome, June 11, 1749, happened in the night of that day. The same was
supposed to have been first a spout, for it is said to be beyond
doubt, that it gathered in the neighbouring sea, as it could be
tracked from Ostia to Rome. I find this in Pere Boschovich's account
of it, as abridged in the Monthly Review for December 1750. In that
account, the whirlwind is said to have appeared as a very black,
long, and lofty cloud, discoverable, notwithstanding the darkness of
the night, by its continually lightning or emitting flashes on all
sides, pushing along with a surprising swiftness, and within three
or four feet of the ground. Its general effects on houses, were
stripping off the roofs, blowing away chimneys, breaking doors and
windows, _forcing up the floors, and unpaving the rooms_ (some of
these effects seem to agree well with a supposed vacuum in the centre
of the whirlwind) and the very rafters of the houses were broken and
dispersed, and even hurled against houses at a considerable distance,
&c.
It seems, by an expression of Pere Boschovich's, as if the wind blew
from all sides towards the whirlwind; for, having carefully observed
its effects, he concludes of all whirlwinds, "that their motion is
circular, and their action attractive."
He observes, on a number of histories of whirlwinds, &c. "that a
common effect of them is, to carry up into the air, tiles, stones,
and animals themselves, which happen to be in their course, and all
kinds of bodies unexceptionably, throwing them to a considerable
distance, with great impetuosity."
Such effects seem to shew a rising current of air.
I will endeavour to explain my conceptions of this matter by figures,
representing a plan and an elevation of a spout or whirlwind.
I would only first beg to be allowed two or three positions,
mentioned in my former paper.
1. That the lower region of air is often more heated, and so more
rarefied, than the upper; consequently, specifically lighter. The
coldness of the upper region is manifested by the hail which
sometimes falls from it in a hot day.
2. That heated air may be very moist, and yet the moisture so equally
diffus'd and rarefied, as not to be visible, till colder air mixes
with it, when it condenses, and becomes visible. Thus our breath,
invisible in summer, becomes visible in winter.
Now let us suppose a tract of land, or sea, of perhaps sixty miles
square, unscreened by clouds, and unfanned by winds, during great
part of a summer's day, or, it may be, for several days successively,
till it is violently heated, together with the lower region of air
in contact with it, so that the said lower air becomes specifically
lighter than the superincumbent higher region of the atmosphere, in
which the clouds commonly float: let us suppose, also, that the air
surrounding this tract has not been so much heated during those days,
and, therefore, remains heavier. The consequence of this should be,
as I conceive, that the heated lighter air, being pressed on all
sides, must ascend, and the heavier descend; and, as this rising
cannot be in all parts, or the whole area of the tract at once,
for that would leave too extensive a vacuum, the rising will begin
precisely in that column that happens to be the lightest, or most
rarefied; and the warm air will flow horizontally from all points to
this column, where the several currents meeting, and joining to rise,
a whirl is naturally formed, in the same manner as a whirl is formed
in the tub of water, by the descending fluid flowing from all sides
of the tub, to the hole in the centre.
And, as the several currents arrive at this central rising column,
with a considerable degree of horizontal motion, they cannot suddenly
change it to a vertical motion; therefore as they gradually, in
approaching the whirl, decline from right to curve or circular lines,
so, having joined the whirl, they _ascend_ by a spiral motion, in the
same manner as the water _descends_ spirally through the hole in the
tub before-mentioned.
Lastly, as the lower air, and nearest the surface, is most rarefied
by the heat of the sun, that air is most acted on by the pressure
of the surrounding cold and heavy air, which is to take its place;
consequently, its motion towards the whirl is swiftest, and so the
force of the lower part of the whirl, or trump, strongest, and the
centrifugal force of its particles greatest; and hence the vacuum
round the axis of the whirl should be greatest near the earth or
sea, and be gradually diminished as it approaches the region of the
clouds, till it ends in a point, as at P in Fig. II. Plate V. forming
a long and sharp cone.
In Fig. I. which is a plan or ground-plat of a whirlwind, the circle
V. represents the central vacuum.