CHAPTER XXXXII.
Section 230. THREE Causes seem generally to concur in producing the Effect of Descent, over Water.
1. The Water itself.
2. The Air above it.
3. Change of Temperature,
Section 231. Article 1. So long as Gass escapes from the Balloon; it will be instantly and reciprocally attracted, throu’ the Crevices, by the Moisture contained in the Air, particularly over Rivers: its specific Gravity within the Balloon, woud be encreased,[52] and consequently the Balloon itself rendered less buoyant:
The Gass woud, on the contrary, be repelled by electric Air: which woud lessen its Tendency to escape, throu’ the Pores of the Silk.
But it is presumed that Air-tight Balloons will be little affected by external Moisture.
231. 2. Moist Air over Water being generally cooler than over the adjacent Land, will, so long as the Gass continues at its former Temperature, assist and raise the Balloon thus moving into a denser Stratum: but no sooner is the Balloon contracted by the external Cold, than it descends into a Medium of Air, whose specific Gravity is proportionable to the contracted Bulk of the Balloon, and rests when equal to it.
231. 3. Water is also a Conductor of Electricity, tho’ a feeble one: and there is moreover a strong chemical Affinity between water, inflammable Air, Gasses, Floguiston, and Electricity.[53]
231. 4. Water will therefore conduct the Gass to itself: i. e. will draw the Balloon downwards, and with accelerating Velocity; as the Attraction is stronger, the nearer the Water.
231. 5. But if the Air over the Water be warmer than that over Land; then the Balloon, moving into a warmer Medium, as over the Sea in frosty Weather, most undoubtedly descends: till the included Gass has received the additional Encrease of Temperature from that of the Air, at which Time it will have a Tendency to re-ascend, and will rest suspended in Equilibrio, as in the former Case.
The above Causes however may be considered, as trivial.
The first may be avoided by making the Balloon Air-tight: and the second easily guarded against by throwing out a little Ballast.
The only formidable one, if any, is
the depression of the atmosphere.
This it will be necessary to consider with some Degree of Attention.
