CHAPTER XI.

Section 68. At 28 Minutes past II. the solid Weights before mentioned were thrown out.

At 29 Minutes the Barometer had fallen to 25 Inches.

[Sidenote: Balloon reascending.]

A Handful of Feathers were sent adrift, which fell quick: demonstrating _likewise_ the Ascent of the Balloon, a second Time: but, tho’ 12 Pounds lighter, it did not seem to regain its original Height: judging +merely+ from this Circumstance, that no more Gass escaped _visibly_ from the Mouth.

[Sidenote: Apparent Size and Situation of the _white_ Flag.]

69. It is somewhat remarkable, that, on repeated Enquiries from unprejudiced Persons, the _white_ Flag, when suspended from the Car above 440 Yards, appeared 4 Yards long: and when at the end of the _half Mile_ Twine, seemed about 8 Yards long, to Spectators from below, in different Places: that sometimes it appeared before, and sometimes behind the Balloon: while to the Observer in the Car, it seemed regularly to follow the Balloon: unless when a _new_ Motion was impressed upon the latter: at which Time the _white_ Flag was situated almost under the Car: or when the Balloon changed its Direction; the Flag being _then_ not always _discoverable_.

When seen _edgewise_ or _foreshortened_; it woud _appear_ to be _nearer_ the Car than it really was.

[Sidenote: Effect of the _white_ Flag on the Balloon.]

70. As there was a Peculiarity attending the Situation of the _half Mile_ Flag, which may prove of singular Use in Airostation; it ought not to be passed over in Silence.

The half Mile Flag hanging loosely from the Car; not perpendicularly under, but following it, frequently at an Angle of about 45 Degrees; shews that the Flag met a Resistance from the Air, unfelt by the Balloon: which out strip’d it, in Proportion to the _greater_ Surface which the Balloon exposed to the Wind.

Taking also into the Account, that the Balloon remained in Equilibrio; while the Flag was subject to the Force of Gravity: which Force was restrained from Exertion, otherwise than as a _Vis Inertiæ_, to keep it always in a perpendicular Situation.

The Resistance of the Air, acting in an horizontal Direction against the _Vis Inertiæ_ of the Flag, must have a Tendency to drive it back: which being ineffectual; the Flag must consequently _rise_; and in rising _will retard the Balloon_.

A Power may therefore be communicated to a Balloon, in the Direction of the Wind, which shall _retard_ its Progress throu’ the Air: a Subject which seems capable of farther Prosecution.