Meteorological Imaginations and Conjectures, [May 1784]
Meteorological Imaginations and Conjectures
The “dry fog” that blanketed much of Europe during the summer of 1783 had occasioned much scientific speculation, but its cause was as yet unknown. In this paper, written nearly a year after the fog first appeared, Franklin was less concerned with its cause (though he did propose a theory that would turn out to be correct) than with its effect, proposing a connection between the summer’s fog and the exceptionally cold winter that followed.1
Franklin docketed this essay “May 1784,” and we are unable to date it more precisely. He sent a fair copy to Benjamin Vaughan well before July 17, when he offered the piece to Thomas Percival for his newly formed Literary and Philosophical Society of Manchester and suggested that Percival get a copy from Vaughan.2 Percival read the essay to the Manchester society on December 22, and it was published in the second volume of the society’s memoirs.3
[May, 1784]
Meteorological Imaginations & Conjectures
There seems to be a Region high in the Air over all Countries, where it is always Winter, where Frost exists continually, since in the midst of Summer on the Surface of the Earth, Ice falls often from above in the Form of Hail.—
Hailstones of the great Weight we sometimes find them, did not probably acquire their Magnitude before they began to descend. The Air being 400 times rarer than Water,4 is unable to support it but in the Shape of Vapour, a State in which its Particles are separated. As soon as they are condensed by the Cold of the upper Regions so as to form a Drop, that Drop begins to fall. If it freezes into a Grain of Ice, that Ice descends. In descending both the Drop of Water and the Grain of Ice, are augmented by Particles of the Vapour they pass thro’ in falling, and which they condense by their Coldness and attach to themselves.
It is possible that in Summer, much of what is Rain when it arrives at the Surface of the Earth, might have been Snow when it began its Descent; but being thaw’d in passing thro’ the warm Air near that Surface, it is changed from Snow into Rain.
How immensely cold must be the original Particle of Hail, which forms the Center of the future Hailstone, since it is capable of communicating sufficient Cold, if I may so speak,5 to freeze all the Mass of Vapour condensed round it, and form a Lump of perhaps 6 or 8 ounces in weight!
When in Summer time the Sun is high, and long every Day above the Horizon, his Rays strike the Earth more directly & with longer Continuance than in Winter; hence the Surface is more heated, and to a greater Depth by the Effect of those Rays.
When Rain falls on the heated Earth, and soaks down into it, it carries down with it a great Part of the Heat, which by that means descends still deeper.
The Mass of Earth to the depth perhaps of 30 Feet, being thus heated, to a certain degree, continues to retain its Heat for some time. Thus the first Snows that fall in the Beginning of Winter, seldom lie long on the Surface, but are soon melted & absorbed. After which the Winds that blow over the Country on which the Snows had fallen are not rendred so cold as they would have been by those Snows if they had remained. The Earth too, thus uncovered by the Snow, which would have reflected the Sun’s Rays, now absorbs them, receiving and retaining the Warmth they afford.6 And thus the Approach of the Severity of Winter is retarded; and the extreme degree of its Cold is not always at the time we might expect it, viz. when the Sun is at its greatest Distance, and the Days shortest, but some Time after that Period, according to the English Proverb which says,
As the Day lengthens,
The Cold Strengthens.—
The Causes of refrigeration continuing to operate, while the Sun returns too slowly & his Force continues too weak, to counteract them.—
During several of the Summer Months of the Year 1783, when the Effect of the Suns Rays to heat the Earth in these northern Regions should have been greatest, there existed a constant Fog over all Europe; and great Part of North America.7 This Fog was of a permanent Nature; it was dry, & the Rays of the Sun seem’d to have little Effect towards dissipating it, as they easily do a moist Fog arising from Water. They were indeed rendred so faint in passing thro’ it, that when collected in the Focus of a Burning Glass they would scarce kindle brown Paper; Of course their Summer Effect in heating the Earth was exceedingly diminished.
Hence the Surface was early frozen.
Hence the first Snows remained on it unmelted, and received continual Additions.
Hence the Air was more chilled, & the Winds more severely cold.
Hence perhaps the Winter of 1783, 4, was more Severe than any that had happened for many Years.
The Cause of this Universal Fog is not yet ascertained.8 Whether it was adventitious to this Earth, and merely a Smoke proceeding from the Consumption by Fire of some of those great burning Balls or Globes which we happen to meet with in our rapid Course round the Sun, and which are sometimes seen to kindle & be destroy’d in passing our Atmosphere, and whose Smoke might be attracted and retain’d by our Earth:9 Or whether it was the vast Quantity of Smoke long continuing to issue during the Summer from Hecla in Iceland, and that other Volcano which arose out of the Sea near that Island;1 which Smoke might be spread by various Winds over the northern Part of the World; is yet uncertain.
It seems, however, worth the Enquiry, whether other hard Winters recorded in History, were preceded by similar permanent & widely-extended Summer Fogs.2 Because if found to be so, Men might from such Fogs conjecture the Probability of a succeeding hard Winter, & of the Damages to be expected by the breaking up of frozen Rivers at the Approach of Spring; and take such Measures as are possible & practicable to secure themselves and Effects from the Mischiefs that attended the last.—3
Notation by Franklin: Meteorological Paper May 1784
8. Also at the Library of Congress is a French translation in BFB’s hand with several minor corrections by BF, and a copy of that translation in the hand of Poullard, Morellet’s secretary, with corrections by BF and Cabanis. As far as we know, BFB’s translation was never published.
9. The copy from which the press copy was made is in the hand of L’Air de Lamotte.
1. He was correct in this hypothesis, as well: G. R. Demarée and A. E. J. Ogilvie, “Bons Baisers d’Islande: Climatic, Environmental, and Human Dimensions Impacts of the Lakagigar Eruption (1783–1784) in Iceland,” in History and Climate: Memories of the Future?, ed. P. D. Jones et al. (New York, Boston, and Dordrecht, Netherlands, 2001), pp. 219–21.
2. BF’s cover letter has not survived. We only know of his sending it to Vaughan because of his July 17 letter to Percival.
3. Literary and Philosophical Society of Manchester Memoirs, II(1785), 357–61. JW, evidently unaware of this publication, submitted the MS to the APS in 1813. It was rejected on account of having been published by the Manchester society: Early Proc. of the APS (Philadelphia, 1884), pp. 440–1.
4. BF first wrote: “being rarer in the upper Regions”. When the essay was printed in the Society of Manchester’s Memoirs, the more accurate estimate of “eight hundred times rarer than Water” was substituted.
5. BF inserted an asterisk here, and in the margin wrote, “A Note * if I may so speak, because perhaps it is not by communicating Cold to the Particles of Vapour that it freezes them; but by depriving them of their Heat.—” This note was not included in the printed version but was incorporated in the French translations.
6. This sentence was added in the margin. It does not appear in the printed version but was included in the French translation.
7. The dry fog was observed in Paris for the first time c. June 18, 1783, and though its origin was then unknown, it is now believed to have been caused by the Lakagígar eruption in Iceland, which began on June 8. Much of Europe was covered by a thick haze from mid-June through at least September: XL, 353; Thorvaldur Thordarson and Stephen Self, “Atmospheric and Environmental Effects of the 1783–1784 Laki Eruption: a Review and Reassessment,” Jour. of Geophysical Research, Atmospheres, CVIII (2003), 2–3, 6–9, 21.
Scholars have searched for evidence that the haze was observable in North America. Though recent discoveries suggest that the higher latitudes of North America may have been affected, there is no proof that the haze appeared in the more populated regions to the south: Richard B. Stothers, “The Great Dry Fog of 1783,” Climatic Change, XXXII (1996), 81–2.
8. Speculation as to the cause of the dry fog began almost immediately, with earthquakes being the most common explanation. In August, Mourgue de Montredon presented a paper to the Académie royale de Montpellier in which he postulated that various subterranean events, including the emergence of a new volcanic island off the coast of Iceland (for which see below), were somehow connected to the appearance of the dry fog, but his explanation was far from being universally adopted. The year 1783 had been full of unusual events, and news of the Lakagígar eruption did not reach the continent until September: Demarée and Ogilvie, “Bons Baisers d’Islande,” pp. 221–30, 237–41; Thordarson and Self, “Atmospheric and Environmental Effects of the 1783–1784 Laki Eruption,” p. 2.
9. BFBF is referring to meteors, then known as “fireballs.” His language suggests that he subscribed to the theory advanced by both John Pringle and David Rittenhouse—a minority position at the time—that meteors were extraterrestrial in origin: XXXIV, 224–5; John G. Burke, Cosmic Debris: Meteorites in History (Berkeley, Los Angeles, and London, 1986), pp. 17–24.
1. Some contemporary reports put the Lakagígar eruption near Mt. Hekla: Mercure de France (Jour.politique de Bruxelles), Oct. 4, 1783, p. 4.
In May volcanic activity off the coast of Iceland created a new, shortlived island called Nyey (New Island). News of this eruption was reported in the Gaz. de Leyde on July 18, 1783, a month after the dry fog first appeared in Paris, and two months before news of the Lakagígar eruption reached France, leading many to assume a connection between the two events: Charles A. Wood, “Climatic Effects of the 1783 Laki Eruption,” in The Year Without a Summer?: World Climate in 1816, ed. C. R. Harington (Ottawa, 1992), p. 71.
2. While it is now accepted that volcanic activity can affect world weather patterns, the exact circumstances by which this occurs are still the subject of debate. The theory that BF advances here has been widely accepted as one possible explanation for how volcanic activity may affect climate: Demarée and Ogilvie, “Bons Baisers d’Islande,” pp. 240–1; Haraldur Sigurdsson, “Volcanic Pollution and Climate: the 1783 Laki Eruption,” Eos, LXIII (1982), 601–2; Wood, “Climatic Effects of the 1783 Laki Eruption,” pp. 69–74.
3. In late February, when the frozen Seine broke up and the winter snow began to melt, low-lying areas were inundated. In his diary, BFB describes two houses on the left bank of the Seine, opposite Passy, that were made a temporary island by the rising water: BFB’s journal, entries of Feb. 26 and 27. Similar flooding occurred all over Europe with disastrous consequences, including severe damage to infrastructure and crops: Rudolf Brázdil et al., “European Floods during the Winter 1783/1784: Scenarios of an Extreme Event during the ‘Little Ice Age,’” Theoretical and Applied Climatology, C (2010), 163, 169–81; Shelby T. McCloy, “Flood Relief and Control in Eighteenth-Century France,” Jour. of Modern History, XIII (1941), 7–12.