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

By Benjamin Franklin

Page 102

shall have found the substance that has it in the
greatest perfection, there will still remain some uncertainty in the
conclusions to be drawn from the degree shown by the instrument,
arising from the actual state of the instrument itself as to heat and
cold. Thus, if two bottles or vessels of glass or metal being filled,
the one with cold and the other with hot water, are brought into
a room, the moisture of the air in the room will attach itself in
quantities to the surface of the cold vessel, while if you actually
wet the surface of the hot vessel, the moisture will immediately quit
it, and be absorbed by the same air. And thus, in a sudden change of
the air from cold to warm, the instrument remaining longer cold may
condense and absorb more moisture, and mark the air as having become
more humid than it is in reality, and the contrary in a change from
warm to cold.

But if such a suddenly changing instrument could be freed from
these imperfections, yet when the design is to discover the
different degrees of humidity in the air of different countries,
I apprehend the quick sensibility of the instrument to be rather
a disadvantage; since, to draw the desired conclusions from it, a
constant and frequent observation day and night in each country will
be necessary for a year or years, and the mean of each different
set of observations is to be found and determined. After all which
some uncertainty will remain respecting the different degrees of
exactitude with which different persons may have made and taken
notes of their observations.

For these reasons, I apprehend that a substance which, though capable
of being distended by moisture and contracted by dryness, is so
slow in receiving and parting with its humidity, that the frequent
changes in the atmosphere have not time to affect it sensibly, and
which therefore should gradually take nearly the medium of all
those changes and preserve it constantly, would be the most proper
substance of which to make such an hygrometer.

Such an instrument, you, my dear sir, though without intending it,
have made for me; and I, without desiring or expecting it, have
received from you. It is therefore with propriety that I address to
you the following account of it; and the more, as you have both a
head to contrive and a hand to execute the means of perfecting it.
And I do this with greater pleasure, as it affords me the opportunity
of renewing that antient correspondence and acquaintance with you,
which to me was always

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Text Comparison with Experiments and Observations on Electricity Made at Philadelphia in America

Page 7
--If you present the point in the dark, you will see, sometimes at a foot distance, and more, a light gather upon it like that of a fire-fly or glow-worm; the less sharp the point, the nearer you must bring it to observe the light; and at whatever distance you see the light, you may draw off the electrical fire, and destroy the repellency.
Page 8
We had even discovered and demonstrated its afflux to the electrical sphere, as well as its efflux, by means of little light windmill wheels made of stiff paper vanes, fixed obliquely and turning freely on fine wire axes.
Page 9
Page 10
As the vessel is just upon sailing, I cannot give you so large an account of American Electricity as I intended: I shall only mention a few particulars more.
Page 12
hook of the other; then there will be an explosion and shock, and both bottles will be discharged.
Page 17
If now the wire of a bottle electrified in the common way, be brought near the circumference of this wheel, it will attract the nearest thimble, and so put the wheel in motion; that thimble, in passing by, receives a spark, and thereby being electrified is repelled and so driven forwards; while a second being attracted, approaches the wire, receives a spark, and is driven after the first, and so on till the wheel has gone once round, when the thimbles before electrified approaching the wire, instead of being attracted as they were at first, are repelled, and the motion presently ceases.
Page 20
Take a bottle in each hand, one that is electrify'd through the hook, the other through the coating: Apply the giving wire to the shot, which will electrify it _positively_, and the cork shall be repelled: Then apply the requiring wire, which will take out the spark given by the other; when the cork will return to the shot: Apply the same again, and take out another spark, so will the shot be electrify'd _negatively_; and the cork in that case shall be repelled equally as before.
Page 22
Page 28
If they are much heated a small spark will do; if not, the spark must be greater.
Page 31
Page 34
and receive what is so discharged.
Page 36
The horizontal motion of the scales over the floor, may represent the motion of the clouds over the earth; and the erect iron punch, a hill or high building; and then we see how electrified clouds passing over hills or high buildings at too great a height to strike, may be attracted lower till within their striking distance.
Page 38
Hence we concluded that the pigeon also had been absolutely blinded by the shock.
Page 40
10 the upper corner.
Page 45
Page 46
So if a tube lined with a [11]non-electric, be rubb'd, little or no fire is obtained from it.
Page 47
You may lessen its whole quantity by drawing out a part, which the whole body will again resume; but of glass you can only lessen the quantity contain'd in one of its surfaces; and not that, but by supplying an equal quantity at the same time to the other surface; so that the whole glass may always have the same quantity in the two surfaces, their two different quantities being added together.
Page 50
Accordingly we find, that if the prime conductor be electrified, and the cork balls in a state of repellency before the bottle is charged, they continue so afterwards.
Page 52
Page 54
[8] See the first sixteen Sections of my former Paper, called _Farther Experiments_, &c.