302. The Aironaut, may, at any Height, marked by looking at the Barometer, when at 24 Inches for Example, or as soon as he finds his Balloon sufficiently expanded, pull up the Rope over a Pulley; or, wind it upon a Reel of two Feet Diameter, within the Car; and continue to do so; till he finds that the Barometer begins to _rise_, (which is a Sign that the Balloon _descends_), by the additional _Weight_ of the Balancer just brought into the Car: on which, by preconcerted Agreement, he may throw out a +white+ Flag, prepared to hang a Yard below the Car. On Sight of the Flag, the Person at the Reel _below_ is to cut the Rope: which Rope, or a Part of it, is to be drawn into the Car. The Balloon will rise no higher; but remain in _Equilibrio_ in the Air, at that Height. CHAPTER LVII. ON BALLOONS. THEIR DEFECTS AND FARTHER IMPROVEMENTS. Section 303. These Defects are best known from the History: a Detail of which is given to the World in an entertaining, elegant, and scientific Manner, by a celebrated Writer on other Subjects, _Mons. Faujas de Saint Fond_, in two Volumes, 12mo. for the two last Years, illustrated with Engravings by the best Masters. And he promises a Continuation, or annual Register of Experiments and Improvements. The Title of the Book is, “Description des Experiences de la Machine aërostatique, &c. &c.” 304. Mr. Cavallo has favoured the British Nation with a cursory tho’ clear Account of the same, in his “History of Airostation:” a Continuation of which it were to be wished he woud likewise publish annually. 305. It might contribute greatly to the Improvement of the Art; if Mr. Faujas woud give Engravings on a large Scale, of the different Machinery, already used or invented to direct the Balloon, with their Proportions: particularly the +moulinet+ of _Blanchard_: as well as that lately tried by Messrs. Auban and Vallet; whose Machinery is still _more distinguished_ and +effectual+. 306. The Titles and Sizes of all useful Books written on the Subject, also the Places where they are to be had, might likewise be inserted, at the End of each _annual_ Volume. 307. The principal Defects of the British Balloons are, in 1. The Construction. 2. Production of Gass. 3. Mode of Direction, and 4. Security of landing. First, Defects of the Construction are both in the Form, and Composition. The Form ought to be that of a +right+[101] _Cylinder_,[102] by which the _Capacity_ is doubled without encreasing the Resistance: ending above and below, each in a Hemisphere. A cylindrical Trunk, 2 Feet in Diameter, being added to convey the Gass _into_ the Balloon; and suffer it to escape, when too much expanded in the etherial Regions. It shoud also be furnished with a Valve, at the Bottom, of equal Diameter with the Trunk: keeping itself Air-tight; and opening outwards by a _given_ Resistance, (as that of ten Pounds Troy,) from the inside Gass.