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. Weigh the whole _Coil_, or any Number of Yards, so as to obtain the whole Weight. Mark the whole Length of the Cord, with different _coloured_ Worsted, or otherways, at the Distance of every eight Yards: as a _sounding_ Line. Note the Marks in a Pocket-Book. These Things being done; give the Balloon, by +inflation+, a Power of Levity _at least_ equal to the known Weight of the Cord: which may be easily obtained by throwing into the Car, already _ballasted_ and prepared, a Weight equal to the Aironaut, together with that of the _Cord_. The Cord must also, previous to the Ascent, be rolled upon a Reel, (made fast in the Ground) whose Diameter shoud be +two+ Feet: each Turn of the Wheel may be called two Yards. A Barometer with an attached Thermometer fixed in the same Frame, also a second or detached Thermometer placed at the Distance of a Yard from the Frame, shoud remain upon the Ground during the Inflation. The same Apparatus of Barometer with attached and detached Thermometer, shoud be suspended in the Car. The Instant the Balloon ascends, an Observer below is to note in a Book the _Point_ at which the Quicksilver stands in each of the +three+ Tubes of the lower Apparatus, also the Time of Ascent: the Aironaut the same.