Free Longitude by Dava Sobel

Graham wrote this endorsement of H-1 and its maker:
John Harrison, having with great labour and expense, contrived and executed a Machine for measuring time at sea, upon such Principle, as seem to us to Promise a very great and sufficient degree of Exactness. We are of Opinion, it highly deserves Public Encouragement, In order to a thorough Tryal and Improvement, of the sever-all Contrivances, for preventing those Irregularityes in time, that naturally arise from the different degrees of Heat and Cold, a moist and drye Temperature of the Air, and the Various Agitations of the ship.
    Despite the hoopla, the Admiralty dragged its feet for a year in arranging the formal trial. And then, instead of sending H-1 to the West Indies, as the Longitude Act required, the admirals ordered Harrison to take his clock down to Spithead and board H.M.S. Centurion , bound for Lisbon. The first lord of the Admiralty, Sir Charles Wager, sent the following letter of introduction to Captain Proctor, commander of the Centurion, on May 14, 1736:
Sir, The Instrument which is put on Board your Ship, has been approved by all the Mathematicians in Town that have seen it, (and few have not) to be the Best that has been made for measuring Time; how it will succeed at Sea, you will be a Judge; I have writ to Sir John Norris, to desire him to send home the Instrument and the Maker of it (who I think you have with you) by the first Ship that comes . . . [T]he Man is said by those who know him best, to be a very ingenious and sober Man, and capable of finding out something more than he has already, if he can find Encouragement; I desire therefore, that you will let the Man be used civilly, and that you will be as kind to him as you can.
Captain Proctor wrote back right away to say,
[T]he Instrument is placed in my Cabbin, for giving the Man all the Advantage that is possible for making his Observations, and I find him to be a very sober, a very industrious, and withal a very modest Man, so that my good Wishes can’t but attend him; but the Difficulty of measuring Time truly, where so many unequal Shocks, and Motions, stand in Opposition to it, gives me concern for the honest Man, and makes me fear he has attempted Impossibilities; but Sir, I will do him all the Good, and give him all the Help, that is in my Power, and acquaint him with your Concern for his Success, and your Care that he shall be well treated . . .
    Proctor needn’t have worried about the performance of Harrison’s machine. It was the man’s stomach that gave him grief. The rough crossing kept the clockmaker hanging over the rail much of the time, when he wasn’t in the captain’s cabin, tending his timekeeper. What a pity Harrison couldn’t fit his own insides with the two dumbbell-shaped bar balances and four helical balance springs that helped H-1 keep its equanimity throughout the journey. Mercifully, the strong winds blew the Centurion swiftly to Lisbon within one week.
    The good Captain Proctor died suddenly as soon as the ship reached harbor, before he’d written up any account of the voyage in his log. Only four days later, Roger Wills, master of H.M.S. Orford , received instructions to sail Harrison back to England. The weather, which Wills recorded as “very mixed with gales and calms,” made for a monthlong voyage home.
    When the ship neared land at last, Wills assumed it to be the Start, a well-known point on the south coast around Dartmouth. That was where his reckoning placed the ship. Harrison, however, going by his sea clock, countered that the land sighted must be the Lizard on the Penzance peninsula, more than sixty miles west of the Start. And so it was.
    This correction greatly impressed Master Wills. Later, he swore out an affidavit admitting his own mistake and praising the accuracy of the timekeeper. Wills gave this certificate, dated June 24, 1737, to Harrison as an official pat on the back. It marked the start of a banner week for Harrison, because on the