I laid the reins upon the neck of my lusts.

-John Bunyan,The Pilgrim’s Progress

DANIEL WAS AWAKENEDone morning by a stifled boom, and supposed it was a piece being tested in the Artillery Yard outside of town. Just as he was about to fall back to sleep he heard it again: thump, like the period at the end of a book.

Dawn-light had flooded the turret of Bedlam and was picking its way down through struts and lashings, plank-decks and scaffolds, dangling ropes and angling braces, to the ground floor where Daniel lay on a sack of straw. He could hear movements above: not blunderings of thieves or vermin, but the well-conceived, precisely executed maneuvers of birds, and of Robert Hooke.

Daniel rose and, leaving his wig behind, so that the cool air bathed his stubbled scalp, climbed up toward the light, ascending the masons’ ladders and ropes. Above his head, the gaps between planks were radiant, salmon-colored lines, tight and parallel as harpsichord-strings. He hoisted himself up through a hatch, rousting a couple of swallows, and found himself within the dome of the turret, sharing a hemispherical room with Robert Hooke. Dust made the air gently luminous. Hooke had spread out large drawings of wings and airscrews. Before the windows he had hung panes of glass, neatly scored with black Cartesian grids, plotted with foreshortened parabolae-the trajectories of actual cannonballs. Hooke liked to watch cannonballs fly from a stand-point next to the cannon, standing inside a contraption he had built, peering through these sheets of glass and tracing the balls’ courses on them with a grease-pencil.

“Weigh out five grains of powder for me,” Hooke said. He was paying attention to part of a rarefying engine: one of many such piston-and-cylinder devices he and Boyle used to study the expansion of gases.

Daniel went over to a tiny scale set up on a plank between two sawhorses. On the floor next to it was a keg branded with the coat of arms of the Silver Comstocks. Its bung was loose, and peppered with grains of coarse powder. Next to it rested a small cylindrical bag of linen, about the diameter of a fist, plump and round as a full sack of flour. This had once been sewn shut, but Hooke had snipped through the uneven stitches and teased it open. Looking in among the petals of frayed fabric, Daniel saw that it, too, was filled with black powder.

“Would you prefer I take it from the keg, or the little bag?” Daniel asked.

“As I value my eyes, and my Rarefying Engine, take it from the keg.”

“Why do you say so?” Daniel drew the loose bung out and found that the keg was nearly full. Taking up a copper spoon that Hooke had left near the scale (copper did not make sparks), he scooped up a small amount of powder from the bung-hole and began sprinkling it onto one of the scale’s frail golden pans. But his gaze strayed towards the linen bag. In part this was because Hooke, who feared so little, seemed to think it was a hazard. Too, there was something about this bag that was familiar to him, though he could not place it in his memory.

“Rub a pinch between your fingers,” Hooke suggested. “Come, there is no danger.”

Daniel probed into the linen bag and got a smudge of the stuff on his fingertips. The answer was obvious. “This is much finer than that in the keg.” And that was the clew that reminded him where he had seen such a bag before. The night that Roger Comstock had blown himself up in the laboratory, he had been grinding gunpowder very fine, and pouring it into a bag just like this one. “Where did this come from? A theatre?”

For once Hooke was flummoxed. “What a very odd question for you to ask. Why do you phant’sy such a thing should come from a theatre, of all places?”

“The nature of the powder,” Daniel said. “Ground so exceedingly fine.” He nodded at the bag, for his hands were busy. Having weighed out five grains of powder from the keg, he poured them from the scale-pan into a cupped scrap of paper and carried it over to Hooke. “Such powder burns much faster than this coarse stuff.” He shook the paper for emphasis and it made a sandy rasp. He handed it to Hooke, who poured it into the cylinder of the Rarefying Engine. Some of these engines were wrought of glass, but this was a heavy brass tube about the size of a tobacco-canister: a very small siege-mortar, in effect. Its piston fit into it like a cannonball.

“I am aware of it,” Hooke said. “That is why I do not wish to put five grains of it into the Rarefying Engine. Five grains of Comstock’s powder burns slow and steady, and drives the piston up in a way that is useful to me. The same weight of that fine stuff from yonder bag would burn in an instant, and explode my apparatus, and me.”

“That is why I supposed the bag might have come from a theatre,” Daniel said. “Such powder may be unsuitable for the Rarefying Engine, but on the stage it makes a pretty flash and bang.”

“That bag,” said Hooke, “came from the magazine of one of His Majesty’s Ships of War. The practice used to be, and still is on some ships, that powder is introduced into the bore of a cannon by scooping it up out of a keg and pouring it in. Similar to how a musketeer charges the barrel of his weapon. But in the heat of battle, our gunners are prone to mis-measure and to spill the powder on the deck. And to have open containers of powder near active cannon is to tempt disaster. A new practice is replacing the old. Before the battle, when it is possible to work calmly, the powder is carefully measured out and placed into bags, such as that one, which are sewn shut. The bags are stockpiled in the ship’s magazine. During battle, as they are needed, they are ferried one at a time to the guns.”

“I see,” Daniel said, “then the gunner need only slash the bag open and pour its contents into the bore.”

Hardly for the first time, Hooke was a bit irked by Daniel’s stupidity. “Why waste time opening it with a knife, when fire will open it for you?”

“I beg your pardon?”

“Behold, the diameter of the bag is the same as the bore of the gun. Why open it then? No, the entire bag, sewn shut, is introduced into the barrel.”

“The gunners never even see what is inside of it!”

Hooke nodded. “The only powder that the gunners need concern themselves with is the priming-powder that is poured into the touch-hole and used to communicate fire to the bag.”

“Then those gunners are trusting the ones who sew up the bags-trusting them with their lives,” Daniel said. “If the wrong sort of powder were used-” and he faltered, and went over and dipped his fingers once more into the bag before him to feel the consistency of the powder inside. The difference between it and the Comstock powder was like that between flour and sand.

“Your discourse is strangely like that of John Comstock when he delivered that bag and that keg to me,” Hooke said.

“He brought them around in person?”

Hooke nodded. “He said he no longer trusted anyone to do it for him.”

Whereat Daniel must have looked shocked, for Hooke held up a hand as if to restrain him, and continued: “I understood his state of mind too well. Some of us, Daniel, are prone to a sort of melancholy, wherein we are tormented by phant’sies that other men are secretly plotting to do us injury. It is a pernicious state for a man to fall into. I have harbored such notions from time to time about Oldenburg and others. Your friend Newton shows signs of the same affliction. Of all men in the world, I supposed John Comstock least susceptible to this disorder; but when he came here with this bag, he was very far gone with it, which grieved me more than anything else that has happened of late.”

“My lord believes,” Daniel guessed, “that some enemy of his has been salting the magazines of Navy ships with bags filled with finely milled powder, such as this one. Such a bag, sewn shut, would look the same, to a gunner, as an ordinary one; but when loaded into the bore, and fired-”