7. The month during which Le Roy and BF were discussing the aurora borealis. See above, under Dec. 7.

8. Denis Diderot, Pensées sur l’interprétation de la nature, (Paris, 1753). He posited that, as Buffon and Leibnitz had suggested, the earth’s core might be made of solid glass and covered with a layer of dust which, due to centrifugal force, would be thickest at the equatorial latitudes and negligible at the poles. Given that glass is the best conductor of electricity, one might attribute to this phenomenon the direction of the magnetic needle and the aurora borealis, which is probably no more than currents of electrical matter. (An earlier edition of the book, entitled De l’interprétation de la nature, added here: “comme on ne manquera pas de s’en assurer avec le cerf-volant du philosophe de Philadelphie.” Denis Diderot, Œuvres complètes, Jean Varloot, ed. [9 vols. to date, Paris, 1975–], XI, 52n.)

9. The work, by the eminent German botanist Johann Georg Gmelin (1709–1755), was his account of a monumental, ten-year-long scientific expedition to Siberia under the auspices of the Russian government. Originally entitled Reise durch Siberien von dem Jahr 1733 bis 1743, its four volumes were published in 1751. The chevalier de Kéralio translated the work, reducing it by half, and published Voyages en Sibérie . . . in 1767.

1. Gmelin detailed two types of auroral displays visible between the beginning of October and Christmas. The more spectacular of the two, he said, consists of pulsating rays converging towards the north, filling the entire sky like a veil of light studded with rubies, sapphires and gold. The phenomenon can be as terrifying as it is beautiful, on account of the crackling and whistling noises which accompany the rays and sound like an enormous display of fireworks. The townsfolk liken the din to a stampede of frenzied animals; foxhunters report that their frightened dogs sink to the ground and cower until the noise subsides.

2. The chaplain had been part of a ship’s crew that had built an air-tight barracks on the coast of the Arctic Sea in which to spend the winter. Their diet consisted of flour, gruel and salt. At the end of October, with the disappearance of the sun and the onslaught of bitter cold and fierce storms, scurvy attacked. By March, when the survivors were found and nursed by locals, there were only eight men left. The chaplain alone had remained healthy, which he attributed to the ventilating chimney he had constructed in his private cell. The scurvy, he claimed, was spread by pernicious vapors emanating from the moist wood of the walls and the clay of the wood-burning stoves.

BF had long believed in the salutary effects of ventilation; see, in particular, XXIII, 486–91.

3. Bookmark.

4. Gmelin reported that in 1685 a well-digging project had discovered that the earth was frozen to a depth of 13 toises, or fathoms, even in the middle of July. The abbé Chappe d’Auteroche of the Académie royale des sciences made a subsequent journey to Siberia by order of the king in 1761. His discussion of the depth of frozen earth in the region Gmelin had visited talks only in terms of pieds. Jean-Baptiste Chappe d’Auteroche, Voyage en Sibérie . . . (Amsterdam, 1769–70), pp. 169, 171–2.