(For which Purpose, Iron-Rings with Spring-Swivels, which open by Pressure of the Fingers, and shut of themselves, might answer better than the leathern Thongs, as the former might be put, in an Instant, round the Cable, and woud run down quicker.)
These Parcels of Ballast are to be sent down, in Succession, till the Balloon has acquired such Degrees of false levity, as will be sufficient to counteract that Tendency which the Wind will have to depress the Car of the Balloon forcibly on the Surface, so long as it is connected with the Grapple on the Ground.
298. 7. When this Point is effected, the Balloon will remain suspended in the Air; and being acted upon by the Wind, will be pressed into a Direction approaching to an horizontal Line, in Proportion to the encreasing Power of the Wind.
And here the Necessity of having the Cable fastened to a Center above the Car, in order to retain its Perpendicularity, is most evident.
The Aironaut, in this Situation, may venture to wind up the Cable gradually, and descend, to the Grapple.
298. 8. Secondly: When the different Currents of Air, have been tried by Descent and Ascent of the Pioneer-Balloon,[99] and found to be all unfavourable; the Aironaut is to rise still higher, into a Calm, pursue his Course horizontally in the blue serene, by propulsive Machinery: estimating the Velocity, by the evident Resistance of the half Mile white Flag described in Section 12, 13. and 12, 15. hanging at a proper Distance below, and of that which hangs loosely at the Side of the Car, to shew a Change in the Direction of the Wind, (then made by a Resistance of the Air): or he may judge o£ the Velocity and Direction, by the Flight of a Feather, repeatedly let loose at certain Intervals of Time.
CHAPTER LVI.
NEW MODE OF ASCENT, TO DETERMINE THE INSTANT THE BALLOON IS ARRIVED AT ANY GIVEN HEIGHT: TO MEASURE THE HEIGHTS: AND TO ESTIMATE THE DENSITIES OF THE AIR AT THE GIVEN HEIGHTS. ALSO, A METHOD OF ASCENDING TO A FIXED BAROMETRIC HEIGHT: THERE TO REMAIN SUSPENDED IN EQUILIBRIO.
Section 299. PREVIOUS to the Ascent, provide a Cord, which shall have sufficient Strength to support twice its own Weight, when so great a Quantity of it is coiled together, as, if extended, woud measure half a Mile or a Mile.