Benjamin Franklin Papers

To Benjamin Franklin from Isaac L. Winn, 12 August 1772

From Isaac L. Winn8

LS: the Royal Society

Winn was a pioneer in this attempt to apply observations on the aurora borealis to forecasting the weather. His hypothesis was related, no doubt accidentally, to two earlier observations: that high winds follow an auroral display, and that a storm moves in an opposite direction from the winds it creates.9 His theory, when Franklin had it published and added comments of his own, attracted considerable scientific attention.1 But it was not, and is not yet, firmly established; evidence of the effect of the aurora on turbulence in the lower air is still slender and conflicting.2 The ship captain, in short, was formulating a problem that the next two centuries have not settled.

Spithead 12 August. 1772


I have often wished that somebody would carefully Collate a sufficient number of Meteorological Journals with intent to observe and Class the several appearances in the Atmosphere before great Changes in the weather, particularly before great Storms. I am perswaded from my own observation that in general sufficient indications of impending Tempests preceed them a Considerable Time, did we but carefully note them. The phaenomenon which I am going to mention is one of those Indications which not only portend an approaching Tempest, but Ascertain from what Quarter it will come; a Circumstance that may render it of Essential Service to seamen. I believe the Observation is new, that the Aurora Borealis is constantly succeeded by hard Southerly or South West Winds, attended with Hazy Weather and Small Rain. I think I am warranted from Experience to say Constantly for in Twenty Three Instances that have occurr’d since I first made the Observation, it has invariably obtain’d. However I beg leave to request you will recommend it to the Notice of the Royal Society, as a matter which when confirmed by Further Observations and Generally known may be of more Consequence than at first Appears. To shew that it may, give me leave to recite the Circumstances which first occasiond my taking Notice of it. Sailing down the English Channel in 1769, a few days before the Autumnal Equinox we had a remarkably Bright and Vivid Aurora the whole Night. In shore the Wind was fluctuating between N.N.W. and N.W. and farther out W.N.W. Desirous of benefiting by the Land Wind and also of taking advantage of earlier Ebb Tyde, I dispensed with the good old Marine Adage (i.e. Never to approach too near a Weather Shore, lest it should prove a Lee Shore) and by short Tacks clung close along the English Coast. Next day the Wind veered to the S.W. and soon after to S.S.W. and sometimes S. We were then in that dangerous Bay between portland and the Start Point and Carried a pressing Sail with hopes of reaching Torbay before dark,3 but Night fell upon us with thick Haze and small Rain, in so much that we could not have seen the Land at the distance of a Ships Length. The Gale was now increased to a storm. In this dilemma nothing remained but to endeavor to keep off the Shore till the Wind should change. Luckily our Ship was a Stout One and well rigged.

Reflecting sometime after on the Circumstances of this Storm and the Phanomena that preceded it, I determined to have particular attention to future Aurora and the Weather that should succeed them and, as I have observed above, in Twenty three Instances have found them uniform except in degree, the Gale generally Commencing between Twenty four and Thirty Hours after the first Appearance of the Aurora. More time and Observation will probably discover whether the Strength of the succeeding Gale is proportionate to the Splendor and Vivacity of the Aurora and the distance of Time between them. I only suspect that the more Brilliant and Active the first is, the sooner will the latter occur, be more Violent, but of shorter duration, than when the Light is languid and dull. Perhaps too the Colour of the Aurora may be some guide in forming a Judgment of the coming Gale. That which preceeded the Storm I have mentiond was exceedingly Splendid. The Tempest succeeded it in Less than Twenty Four Hours, was Violent, but of short (about Eight Hours) Continuance. In June last a little without soundings we had for Two Nights following faint inactive Aurora; the Consequent Gale was not hard but lasted near Three Days, the First day attended with Haze and small rain, the Second with Haze only and the last day Clear.

The Benefit which this observation on the Aurora Borealis when further confirmd and known may be of to Seamen is obvious in Navigating near Coasts which tend East and West, particularly in the British Channel. They may, when warnd by the Aurora Borealis, get into port, and Evade the impending Storm, or, by Stretching over to the Southward, facilitate their Passage, by that very Storm, which might have destroyed them; for no Winds are so dangerous in the Channel as Southerly and South West. In a word, since I have made this observation, I have got out of the Channel, when other Men as alert, and in faster Sailing Ships, but unapprized of this Circumstance, have not only been driven back, but with difficulty have escaped Shipwreck. Perhaps the observation, that Southerly Gales constantly succeed these Phaenomena, may help to account for the Nature of the Aurora Borealis: my own thoughts on that Subject I shall sometime beg leave to lay before you. I am with great Respect Sir, Your Obliged Humble Servant

I L Winn

Addressed: Benjamin Franklin LLD London

[Note numbering follows the Franklin Papers source.]

8For the merchant captain see above, XVII, 49 n.

9The first hypothesis was expounded by Henry Beighton in Phil. Trans., XL (1737–8), 263–4; the second was BF’s: above, III, 149, 392 n, 463–5; IX, 110–12. For BF’s long-standing interest in the aurora see above, II, 185–6; IV, 268, 298–9; VII, 358.

1The publication was in Phil. Trans., LXIV (1774), 128–32; BF’s comments are the following document. For the attention subsequently given the theory see Richard Kirwan, “An Essay on the Variations of the Barometer,” Royal Irish Academy Trans., II (1788), 62–5, 70–2; Alexander McAdie, The Aurora in Its Relations to Meteorology (Washington, 1885), pp. 13, 15, 18–21.

2J. Alan Chalmers, Atmospheric Electricity (2nd ed., Oxford, etc., [1967]), pp. 45–6, 173–4.

3In southerly gales Lyme Bay, near Portland, was exposed, whereas Torbay offered a sheltered anchorage.

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