CHAPTER XXVII

USEFUL CONCLUSIONS.

[Sidenote: Change in the _Form_ of the Balloon while descending: with Conclusions drawn from the Change.]

Section 159. It was remarkable that, the lower Parts of the Balloon regularly adopted a _similar_ Form at each Descent: not unlike a _Ship’s Bottom_; looking up, at the Head or Prow, while on the Stocks: the _Neck_ of the Balloon forming a beautiful _central_ Pillar; in Shape like that of a _Speaking Trumpet_ inverted.

[Sidenote: Time of Descent discovered by the Form of the Balloon.]

And hence may be derived a Piece of _useful_ Information: as the _precise_ Time of descending is discovered by bare _Inspection_ of the Machine.

[Sidenote: Balloon adopting the Form of an elliptic Solid.]

160. Another Conclusion seems likewise deducible from the above, that if the Balloon is so burdened, as to _descend_ while it retains the Form of an +elliptic solid+;[44] it will descend more rapidly, than if it contained less Gass: the Force of Descent in both Cases being supposed the same.

For if the Diminution of Gass be so great as _not_ to fill the upper Hemisphere of the _Balloon_; the Resistance of the atmospheric Air _below_ woud probably give _it_ the Appearance of a _Concave_ or Umbrella, which woud greatly _check_ the Descent: viz. in Proportion to the Square of the Number of Feet of which the Surface was composed.

[Sidenote: An equatorial Hoop prefered to a Parashute.]

161. Hence also the evident Utility of an +equatorial hoop+ for Balloons: in Preference to a Parashute, which woud be only an Incumbrance.