From Jean-Baptiste Le Roy
AL: American Philosophical Society
Thursday Morning [August, 1778?]8
I send you Dr. Forster’s Observations made during a voyage round the World and I have marked the page wherein he explains the formation of Those Ilands I spoke to you of and That are hardly higher than high water mark.9 I have marked equally The page wherein he speaks of that curious observation They made aboard a ship at Tahity where they saw the fire running down the chain into the water &c.1 Since I left you my Dear Doctor I reflected on your explanation of the splitted wood in sundry pieces by the Lightning but Tho’ it seemed to me at first to give a good reason of that curious Phaenomenon nevertheless in considering afterwards more attentively of it I thought there was two very strong objections against it.
1st That it splits not only trees but even dry very dry wood such as laths and Beams of roofs in which there seem to remain but very few particles of Water.
2dly That in the wood the water is so disseminated and so spread amongst all its particles of it That the action of that Water must be very Weak and So little able, to produce such violent effects for if the force of the water reduced in Vapour is very strong it is when there is a certain collection of particles together as the Canon Powder of which a certain number collected in a Heap and lighted at once may blow up a House for instance but when spread and disseminated if I may say so, in the whole Mass of the House so that There be a grain of powder there and There you might light the whole I believe without a great effect and I have some notion that amongst the different fire Works there are some made upon that Principle viz. to produce a great fire but with a small explosion.
You know furthermore with what force the water freezing spreads and Breaks Glasses, earthen and China Pots, and even green Barrels and that those violent effects are produced only by the different particles of the air disseminated in the water that unite together and by that Mean acquire The force of Breaking and tearing all that opposes Their action. And a great proof of this is That if you lett the small particles of air go out as they are expelled of the intervals of the particles of water all Those violent effects of the water freezing do not take place and the freezing goes on quietly without any explosion. But your Superior Genius My Dear friend will may be answer these objections and Dispell The Cloud that This Seems to spread upon your Explanation.
Addressed: A Monsieur / Monsieur Franklin deputé / du Congrès / à Passy
8. On July 30, Forster sent his book to BF who must have received it some time in August, and lent it to Le Roy, who is now returning it. See also Vaughan to BF, Aug. 1.
9. The formation of what Cook called the “half-drowned islands,” known today as the Tuamotu Archipelago, was the subject of lively scientific speculation. Forster’s son George, who accompanied his father on Cook’s expedition, wrote: “It remains a subject worthy the investigation of philosophers, to consider from what probable principles these islands are so extremely numerous, and form so great an archipelago to windward of the Society islands. …” George Forster, A Voyage Round the World … (2 vols., London, 1777), II, 46. The father’s theory, offered on pp. 150–1 of his Observations, was that they were fundamentally the product of coral-like animals called lithophytes, and that decomposing organic material from the sea had formed on them a thin layer of soil sufficient to sustain vegetation.
1. “The isles in the South-Sea are … subject to lightening and thunder storms; for we experienced some at different places and seasons, in the several parts of our voyage over this ocean; and we were now and then obliged to fix the electric chain, to prevent fatal accidents. Once at O-Taheitee, the man who was sent up to the main top-gallant mast head, had scarcely fixed the chain, and another man was still clearing it of the main-chains and shrouds, when the latter received an electric shock, and the fire was seen running down the chain into the water, without doing any damage.” Forster, Observations, p. 119.