i] Puitapeveuia, May 3, 1753.
Dear Sir,
I received your essay last post, and my presses being at
present engaged in some public work that will not admit of
delay, I have engaged Mr. Parker to print it out of hand at
New-York. You may expect to see it done in two or
three weeks. The pacquet was not sealed, and I observed
that the tables showing the culture of sundry fields were
not with the rest of Mr. Jackson’s papers. Perhaps you
did not design them for the press.
I wish the Barbary barley may grow. I have some of it
and sowed it; but it seemed to me to have been cut too
green. Ihave formerly heard it reckoned the finest barley
in the world, and that it makes a great part of the food of
the inhabitants.
I think I have never been more hurried in business than
at present ; yet I will steal a few minutes, to make an ob-
servation or two on Mr. Todd’s ingenious letter to you.
-
The supposing a mutual attraction between the par-
ticles of water and air, does not seem to me to be introdu-
cing a new law of nature ; such attractions taking place in
many other known instances.
-
Water is specifically eight hundred and fifty times
heavier than air. To render a bubble of water then spe-
cifically lighter than air, it seems to me that it must take
up more than eight hundred and fifty times the space it did
before it formed the bubble ; and within the bubble should
be either a vacuum, Or air rarified more than eight hundred
and fifty times. Ifa vacuum, would not the bubble be im-
mediately crushed by the weight of the atmosphere’. And
no heat we know of will rarify the 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. Be-
Original Letters of Dr. Franklin. 165
sides, water agitated ever so violently produces no heat, as
has been found by accurate experiments.
-
A hollow sphere of lead, has a firmness and consisten-
cy in it, that a hollow sphere of fluid unfrozen water cannot
be supposed to have. The lead may support the pressure
of the water ’tis immerged in, but the bubble could not sup-
port the pressure of the air if empty within.
-
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 them-
selves though filled with warm breath.
-
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, or
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 in-
spired and expired, (perhaps in a bladder) has, or has not
acquired more moisture than our common air in the damp-
est weather.
As to the precipitation of water in the air we breathe,
perhaps it is not always a mark of that air’s being overload-
ed. In the region of the clouds, indeed, the air must be
overloaded (its coldness considered) if it lets fall its water
in drops, which we call rain; but those drops may fall
through a dryer air near the earth; and accordingly we
find, that the hygroscope sometimes shows 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 on our wainscots, seems more cer-
tainly to denote an air overloaded with moisture, and yet
this is no sure sign. For after a long continued cold sea-
son, ifthe air grow suddenly warm, the walls, &c. continu-
ing their coldness longer, will for some time condense the
moisture of such air, ’till they grow equally warm; and
then they condense no more, although the air is not become
dryer. And on the other hand, after a warm spell, if the
air grow cold, though moister than before, the dew is not
166 Original Letters of Dr. Franklin.
so apt to gftes on the warm 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.
-
’Tis, I think, a mistake, that the trade winds blow on-
ly 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 coast indeed blow chiefly in
the afternoon. In the very long run from the west side of
America, to Guam among the Philippine islands, ships sel-
dom have occasion to hand their sails, and yet they make
it in about sixty days, which could not be if the wind biew
only in the afternoon.
-
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 N. E. or therea-
bouts, and it gradually grows more east as you approach the
line. The same observation is made of its changing from S,
E. to E. gradually, as you come from the south latitudes to
the equator.
I have not yet had time to transcribe my paper on the in-
crease of mankind, but hope to do it shortly, and shall be
lad of your and Mr. Todd’s sentiments on it. My re-
spects to that gentleman; and be assured that I am, very
affectionately, dear Sir,
Your most humble servant,
B. FRANKLIN.
|
|