For as the Effect of the Moon’s Attraction is to diminish the Weight of the Atmosphere (tho’ its Quantity be increased) by elevating the Column of Air in the Line of her Meridian; the Rarefaction of the Air is therefore encreased, first at the Top of the Atmosphere; afterwards it gradually descends to the Bottom, or Surface of the Earth: so that the incumbent Weight being diminished, the Air beneath will be greatly expanded.
At whatever Height therefore any Quantity of Vapour or superior Cloud rested, while the Moon was in her Quarter; it woud gradually descend at the Approach of the next New or Full: at which Times it woud remain suspended at a Height, where an Expansion took Place equivalent to the former Expansion, at the Moon’s Quarter: and, if the Height during the Moon’s Quarter was only equal to that of common Clouds; such Vapour woud, at the New and Full Moon, descend in Mist, Rain, Snow, or Wind.
293. Little Reliance is to be placed, in these Northern Climates, on the aggregate Weight (or elastic Power) of the Air, indicated by the Height of the Barometer, near the Times of the New and Full Moons: tho’, in general, it will descend about those Times.
These Things being so; it woud be improvident to undertake an aërial Excursion, either three Days before, or three Days after the Day, either of the New, or Full Moon: the Ascent shoud be forborne every other Week; at least till the ArtProper Days for Ascent. is a little more advanced.
The two remaining alternate Weeks in each Month, viz. when the Moon is in the Quarters, and the Tide of Air flowing throu’ the Atmosphere, is checked, counterbalanced, and equalized, by the lateral Attractions of the Moon and Sun, acting at right Angles, i. e. on different Parts of the Air, pendent on the Earth’s Surface;—more settled and regular Weather may be naturally expected; and particularly freer from the Extremes of Wind and Cold.
Moreover, as the Almanack, and Ephèmeris[96] may be always consulted; the Day fixed on shoud not be marked with Conjunctions of the Planets.[97] The Inequality of their united Attractions greatly deranges the Equilibrium of the upper Parts of the Atmosphere; producing sudden Squalls and Gusts of Wind: which, tho’ of short Continuance, perhaps a few Hours, are inauspicious to the successful Inflation and Ascent of a Balloon, during the Infancy of the Science. (See [Section 211].)
CHAPTER LIII.
ON THE MEANS OF SUSTAINING A BALLOON ABOVE THE SURFACE OF THE WATER, BY A TEMPORARY LOSS OF BALLAST: AND OF RECOVERING THE BALLAST.
Sect. 294. Art. 1.THE two Inconveniencies arising from a Discharge of Ballast, while the Balloon is under the Pressure of a mediocèanal Column of Air, are,