Memoirs of Benjamin Franklin; Written by Himself. [Vol. 2 of 2] With his Most Interesting Essays, Letters, and Miscellaneous Writings; Familiar, Moral, Political, Economical, and Philosophical, Selected with Care from All His Published Productions, and Comprising Whatever Is Most Entertaining and Valuable to the General Reader

By Benjamin Franklin

Page 210

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 curved 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, _Fig. 2. in the plate_, forming a long and sharp cone.

In figure 1, which is a plan or groundplat of a whirlwind, the circle V
represents the central vacuum.

Between _a a a a_ and _b b b b_ I suppose a body of air, condensed
strongly by the pressure of the currents moving

Last Page Next Page

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

Page 34
_ Read at the Royal Society, July 8, 1756.
Page 90
I will not trouble you at present with my fancies concerning the manner of forming the rest of our system.
Page 103
You may possibly remember, that in or about the year 1758, you made for me a set of artificial magnets, six in number, each five and a half inches long, half an inch broad, and one eighth of an inch thick.
Page 115
Accordingly, about the middle of October last, I went with some friends to Portsmouth; and a day of wind happening, which made a lee-shore between Haslar-hospital and the point near Jillkecker, we went from the Centaur with the long-boat and barge towards that shore.
Page 145
the ship grind them as fine as mustard.
Page 148
| | | |----+-------+----+-----+----+------+-----+-----+-----+------------------| | Apr| | | | | | | | | | | 10| | | 62 | | | | | | | | 11| | | 61 | | | | | | | | 12| | | 64 | | | | | | | | 13| | | 65 | | | | | | | | 14| | | 65 | | | | ° ′| ° ′| | | 26| .
Page 164
| 80 | 77 | | 23 |35 35 |40 52| 7 | 77 | 78| 75 |North|W ¼ S | 100 | | omitted.
Page 176
But an old workman observing it advised me not to do so, telling me I might lose the use of my hands by it, as two of our companions had nearly done, one of whom, that used to earn his guinea a week, could not then make more than ten shillings, and the other, who had the dangles, but seven and sixpence.
Page 225
It is this.
Page 247
By a push with your tongs or poker, you turn it on its pin till it faces the back of the chimney, then turn it over on its axis gently till it again faces the room, whereby all the fresh coals will be found under the live coals, and the greater part of the smoke arising from the fresh coals will in its passage through the live ones be heated so as to be converted into flame: whence you have much more heat from them, and your red coals are longer preserved from consuming.
Page 270
I cannot but applaud your zeal for preserving the purity of our language both in its expression and pronunciation, and in correcting the popular errors several of our states are continually falling into with respect to both.
Page 279
| | z |(ez) Wages.
Page 287
_Questions discussed by the Junto forming the preceding Club[74].
Page 292
be read by the youth, and the difficulties, that may occur to them, be explained by the master.
Page 328
But I think the offence much greater in those who either directly or indirectly have been concerned in making the very laws they break.
Page 330
"Every man.
Page 340
Page 359
Page 367
_Flies_, drowned in America, brought to life in England, ii.
Page 393
Asterisks were used by the editor to indicate omitted text.