The Complete Works in Philosophy, Politics and Morals of the late Dr. Benjamin Franklin, Vol. 2 [of 3]

By Benjamin Franklin

Page 208

Suppose the distance to be half
an inch, and the door eight feet high, you find thence that your room
requires an entrance for air equal in area to ninety-six half inches,
or forty-eight square inches, or a passage of six inches by eight.
This however is a large supposition, there being few chimneys, that,
having a moderate opening and a tolerable height of funnel, will not
be satisfied with such a crevice of a quarter of an inch; and I have
found a square of six by six, or thirty-six square inches, to be a
pretty good medium, that will serve for most chimneys. High funnels,
with small and low openings, may indeed be supplied thro' a less
space, because, for reasons that will appear hereafter, the _force
of levity_, if one may so speak, being greater in such funnels, the
cool air enters the room with greater velocity, and consequently
more enters in the same time. This however has its limits; for
experience shows, that no increased velocity, so occasioned, has
made the admission of air through the key-hole equal in quantity to
that through an open door; though through the door the current moves
slowly, and through the key-hole with great rapidity.

It remains then to be considered how and where this necessary
quantity of air from without is to be admitted so as to be least
inconvenient. For if at the door, left so much open, the air thence
proceeds directly to the chimney, and in its way comes cold to your
back and heels as you sit before your fire. If you keep the door
shut, and raise a little the sash of your window, you feel the same
inconvenience. Various have been the contrivances to avoid this, such
as bringing in fresh air through pipes in the jams of the chimney,
which, pointing upwards, should blow the smoke up the funnel; opening
passages into the funnel above, to let in air for the same purpose.
But these produce an effect contrary to that intended: for as it
is the constant current of air passing from the room _through the
opening of the chimney_ into the funnel which prevents the smoke
coming out into the room, if you supply the funnel by other means or
in other ways with the air it wants, and especially if that air be
cold, you diminish the force of that current, and the smoke in its
effort to enter the room finds less resistance.

The wanted air must then _indispensably_ be admitted into the
room, to supply what goes off through the opening of the

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Text Comparison with Benjamin Franklin and the First Balloons

Page 0
Page 1
There it was held down by a Cord till 5 in the afternoon, when it was to be let loose.
Page 2
I thought it my Duty, Sir, to send an early Account of this extraordinary Fact, to the Society which does me the honour to reckon me among its Members; and I will endeavour to make it more perfect, as I receive farther Information.
Page 3
The great one of M.
Page 4
The Night was quite calm and clear, so that it went right up.
Page 5
Most is expected from the new one undertaken upon subscription by Messieurs Charles and Robert, who are Men of Science and mechanic Dexterity.
Page 6
_ When they were as high as they chose to be, they made less Flame and suffered the Machine to drive Horizontally with the Wind, of which however they felt very little, as they went with it, and as fast.
Page 7
The other Method of filling a Balloon with permanently elastic inflammable Air, and then closing it is a tedious Operation, and very expensive; Yet we are to have one of that kind sent up in a few Days.
Page 8
We should not suffer Pride to prevent our progress in Science.
Page 9
With great and sincere Esteem, I am, Dear Sir, Your most obed^t & most humble Servant, B.
Page 10
Several Bags of Sand were taken on board before the Cord that held it down was cut, and the whole Weight being then too much to be lifted, such a Quantity was discharg'd as to permit its Rising slowly.
Page 11
Charles hier a 10 heures 1/4 du Soir et a dit, Que les Voyageurs etoient descendus lentement et volontairement a trois heures 3/4 dans les Marais de Nesle et d'Hebouville, une lieue et demie apres l'Isle Adam.
Page 12
_ The hand-writing is in a more flowing style than the subsequent letters.
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The following possible mispellings have been retained: p.