Note 99 — Chapter LV
Reading edition
To find the Direction of an upper Current, without the Inconvenience of rising above the Level which the Aironaut has fixed on.
This the Abbé Bertholon has hinted at, by Means of a smaller Balloon.
The Dimensions of which, must however be so large; that, allowing for the Evaporation of Gass, it will just rise with the Weight of a Quantity of Cord, a Mile and half, for Instance, in Length: and have sufficient Room left within, to admit of the Expansion of Gass without Rupture.
The Pioneer-Balloon may be taken up, empty, and filled with Gass necessarily escaping from the mouth of the great Balloon, when stationary: and may be sent up with a Cord, fastened to the Center above the Car of the great Balloon, to reconnoitre the superior Currents: or it may be only filled in Part; and made to descend, and discover the lower Currents.
See “Des Avantages de Ballons, &c. Page 72.”