_____We meet the Veery brothers, Cosmo and Damian, who make beeswax effigies to be hanged and burned at political rallies -- sometimes, if the effigies are to be decapitated, using spare parts from the neighborhood abattoir. They're so lifelike, Damian says, that "you'd enter any darken'd Room our lads and lasses happen'd to be in, only upon ill advice indeed." Mason and Dixon have discovered that the back rooms of taverns in Philadelphia tend to be reserved for members of various secret societies, and in one of them he finds some of the Veery brothers' creations: heads of the commissioners for the boundary line. So he's creeped out when he attends a meeting of the commissioners. "Those waxen Faces that gaz'd at him with such a midnight Intent, -- here are their daytime counterparts to greet him, with the same, O God in thy Mercy, the same look ... as if deliberately to recall the other night."
Mason finds it hard to sleep in Philadelphia, what with the street noises and the bedbugs, though Dixon has no problem doing so. One insomniac night he goes to the Orchid Tavern, where he has the complexities of Pennsylvania politics -- the reason the Veery brothers can make a living off of effigies -- explained to him. "Religious bodies here cannot be distinguished from Political Factions. These are Quaker, Anglican, Presbyterian, German Pietist. Each prevails in its own area of the Province." The Penns, he is told "tho' Quaker by ancestry are Anglican in Praxis, -- some even say, Tools of Rome." But the political lesson is interrupted by the appearance of Franklin, who gives a demonstration of electricity with the help of volunteers from the audience.
Mason and Dixon's work on their eponymous line begins with the establishment of the southernmost boundary of Philadelphia. The boundary between Pennsylvania and Maryland is to be drawn fifteen miles south of this. The commissioners have chosen the northern wall of a house to be the southernmost boundary, because the south wall is in private property. Nearby, "Mr. Benjamin Loxley and his Crew have been busily erecting an Observatory." Dixon, who is in charge of the compass, visits a coffee house, the Flower-de-Luce, which is "frequented by those with an interest in the Magnetick." There he meets "Dr. Franklin's friend Dolly," who turns out to be interested in compasses and maps. She tells him that the Calverts are interested in him and that Cecilius Calvert "believes you a Wizard, a Dowser of Iron.... They imagine, that you and your Instrument will make of them Nabobs, like Lord Lepton, to whose ill-reputed Plantation you must be drawn, upon your way West, resistlessly as the Needle. Then, Sailor among the Iron Isles, -- Circumferentor Swab, -- Beware."
Late in December they awaken to silence outside, which they find eerie, so they set out to find out what has happened to everyone. At the Restless Bee, a coffee house, they learn that the vigilantes known as the Paxton Boys have massacred a group of peaceful Indians and are now marching on Philadelphia. "Mason and Dixon look at each other bleakly. 'Well. If I'd known 'twould be like this in America....' Mason did note as peculiar, that the first mortal acts of savagery in America after their Arrival should have been committed by Whites against Indians." They also worry about the kind of people they will encounter as they move west. "What must we look like? A sizable Band of Arm'd Pioneers, working for the Proprietors? ... mystical Machinery they've never seen ...? Up far too late at night, gazin' at the Heavens...?"
They also recall the Second Jacobite Rising of 1745, although Mason, who was seventeen at the time, while Dixon was twelve, claims to recall it better. Which leads them into a quarrel about the difference of their backgrounds, with Mason asserting, "You, simple Geordie, inhabit a part of England where ancient creatures may yet move in the Dusk, and the animals fly, and the dead pop in now and then for coffee and a chat. Upon my home soil, the Ground for growing any such Wonders has been cruelly poison'd, with the coming of the hydraulick Looms.... My home's no more."
Pitt and Pliny are excited by the notion that Mason and Dixon might have come to blows over their differences, but Cherrycoke doesn't give them that satisfaction, assuring them that they remained friends "till something ... something occurr'd between them, in 'sixty-seven or 'sixty-eight, that divided their Destinies irremediably...." Tenebrae announces that it's bedtime for the boys, but Cherrycoke promises them "Indians tomorrow." After they depart, he tells the remaining audience about the watch that Emerson presented to Dixon before he sailed, telling him to "be vigilant, to the point of Folly, if Folly it takes, in your care of this Watch, for within it lies a secret mechanism, that will revolutionize the world of Horology." In short, it's a perpetual motion machine, which Emerson has always told Dixon is impossible. But when Dixon goes to wind it, he can't find a way of doing so.
Mason is skeptical about this impossible watch, even though Dixon assures him that he never has to wind it. "You might be winding it while I'm asleep, or when screen'd, as we so often are one from the other, by Trees." Then one night Dixon has a dream in which Emerson appears to him and charges him with breaking his contract and threatens terrible consequences. After he awakes, "Tho' sworn to guarantee the Watch's safety, he soon finds his only thoughts are of ways to rid himself of it." As it happens, a land-surveyor named R.C., who is working with them, has been shown the watch and wants it, thinking it might be worth something to the men who are trying to solve the problem of determining longitude. So one night R.C. swallows the watch.
In the months, and then the years, after he swallows the Watch, as the days of ceaseless pulsation pass one by one, R.C. learns that a small volume within him is, and shall be, immortal. His wife moves to another Bed, and soon into another room altogether, after persuading him first to build it onto the House. "Snoring's one thing, R.C., I can always do something about that," brandishing her Elbow, "-- but that Ticking..."Dixon reluctantly reports the loss of the watch to Emerson, who is surprisingly jubilant at the news. He has to dictate his reply to Dixon's letter because he injures himself celebrating the news of the lost watch, but Mrs. Emerson writes that her husband "wishes me to say, 'Felicitations, Fool, for it hath work'd to Pefection.'" But the only explanation of that remark from Emerson comes in a postscript: "Time is the Space that may not be seen, --"