335. The Abbée Bertholon wrote in 1784: and has particularly mentioned the following Points, as capable of ample Investigation, and. Discussion. Sect. 336. Art. 1. _The Temperature of the Air at different Heights._ Which will determine whether the Atmosphere be _practically Navigable_, at all Times and Places. 336. 2. _The dissolvent Power of the Air by Means of an Atmometer for Evaporation._ Probably the Height may be determined, to which Clouds commonly ascend in order to find the proper horizontal Level, in which Balloons can move with the greatest Ease, Safety, and Expedition. 336. 3. _Variations of the Barometer._ This will ascertain the exact Height, without Mensuration. 336. 4. _The_ +densities+ _at different Heights_. A principal Object in de Luc’s abstruse and scientific Researches: not only useful but necessary to determine the Laws of Refraction; without which, Astronomy, and consequently +navigation+, must remain defective. 336. 5. _The different Effects of Tastes and Odors, at different Heights_: _Experiments on Plants and Animals: also of_ +sound+.[111] These may produce new and salutary Effects on the human Body: and determine how far a Change from hot, putrid, and impure, to cool pure Air, impregnated with the invigorating aërial Acid, may contribute, without the Aid of Drugs, to the Recovery of the Sick, and Invalid: or promote Longevity. 336. 6. _The Direction and Velocity of the Wind._ The different Currents and their different Heights, the Limitation of each Stratum of Wind, together with their different Temperatures at the same Time, will point out the proper Paths for the Balloon to move in, at all Times, and _possibly_ without the Necessity of accurate Direction: the Mode of Ascent and Descent being _already_ known, and proper Instructions given for a secure Landing. 336. 7. _Electricity of the Air_, +meteors+. This may lead to the Birth Place of Lightening, and Methods how to avoid its Effects in the Air. Tho’ it be already known, that little Danger is to be apprehended, on Account of the mutual Repellency between the electric Fluid, inflammable Gass, and oiled Silk. The Irides, the Coronaes, Haloes, and other Phenomena of Colours: the Generation and Solution of which may be investigated on the Spot. 336. 8. _Geography may become a new Science._ 336. 9. _Use of the Balloon for Signals in the calm Air, above Molestation; above Winds still blowing below: to discover the Positions of an Army, or Navy._[112] 336. 10. _To throw principal Men into a Town: and convey others out of it._ 336. 11. With the Montgolfier Balloon, to try Experiments on Light, and Fire: to transport great Weights: raise them out of the Water: draw up Piles, raise Trees, Vessels, &c.