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Atlantic Ship Crossings and the Motion of the Earth

To Cadwallader Colden


I receiv’d yours with others enclos’d for Mr. Bertram and Mr. Armit, to which I suppose the enclos’d are Answers. The Person who brought yours said he would call for Answers, but did not; or, if he did, I did not see him.

I understand Parker has begun upon your Piece. A long Sitting of our Assembly has hitherto hinder’d me from beginning the Miscellany. I shall write to Dr. Gronovius as you desire.

I wish I had Mathematics enough to satisfy my self, Whether the much shorter Voyages made by Ships bound hence to England, than by those from England hither, are not in some Degree owing to the Diurnal Motion of the Earth; and if so, in what Degree? ‘Tis a Notion that has lately entred my Mind; I know not if ever any other’s. Ships in a Calm at the Equator move with the Sea 15 Miles per minute; at our Capes suppose 12 Miles per Minute; in the British Channel suppose 10 Miles per Minute: Here is a Difference of 2 Miles Velocity per Minute between Cape Hinlopen and the Lizard! no small Matter in so Weighty a Body as a laden Ship swimming in a Fluid! How is this Velocity lost in the Voyage thither, if not by the Resistance of the Water? and if so, then the Water, which resisted in part, must have given Way in part to the Ship, from time to time as she proceeded continually out of Parallels of Latitude where the Earths Motion or Rotation was quicker into others where it was slower. And thus as her Velocity tends eastward with the Earth’s Motion, she perhaps makes her Easting sooner. Suppose a Vessel lying still in a Calm at our Cape, could be taken up and the same Instant set down in an equal Calm in the English Channel, would not the Difference of Velocity between her and the Sea she was plac’d in, appear plainly by a violent Motion of the Ship thro’ the Water eastward? I have not Time to explain my self farther, the Post waiting, but believe have said enough for you to comprehend my Meaning. If the Reasons hinted at should encline you to think there is any Thing in this Notion, I should be glad of an Answer to this Question, (if it be capable of a precise Answer) viz.

Suppose a Ship sails on a N. East Line from Lat. 39 to Lat. 52 in 30 Days, how long will she be returning on the same Line, Winds, Currents, &c. being equal?

Just so much as the East Motion of the Earth helps her Easting, I suppose it will hinder her Westing.

Perhaps the Weight and Dimensions or Shape of the Vessel should be taken into the Consideration, as the Water resists Bodies of different Shapes differently.

I must beg you to excuse the incorrectness of this Scrawl as I have not time to transcribe. I am Sir Your most humble Servant

February, 1746