The device was finished in the spring of 1662, almost twenty years to the day after Galileo's death and a fortnight into Isaac Newton's most recent round of not sleeping, although its completion had nothing to do with the former and everything to do with the latter.

Despite the length of time it had taken from beginning to end, the building of the device itself had not been trying; two round boxes, equal in weight, size, and shape, now hung from cords in their room where beds and desks and endless paper stacks had once stood. Both boxes and cords had been purchased by Daniel, although Isaac had maintained that building everything by hand would allow more complete control of the variables. Daniel had eventually overridden him on the grounds that cord-making was a loud and messy process, and that such activities would probably put an end to their already lukewarm welcome in the college dorms.

So no, the building had not been difficult in the end. The difficult part, the part that had consumed Daniel's nights and days for nearly four months, was the collecting of the materials. Isaac had demanded nine substances, carefully measured and weighed to ensure that each was equal to the last, and what Isaac demanded, Daniel found himself bound to produce, out of helpless curiosity if nothing else.

There was one of wood and one of wheat piled on the floor near the south-western corner of Daniel's bed; on Isaac's desk, in small containers – whose own weights had been measured, compared, and subtracted – were sand, salt, and water respectively. Finally, spaced out on the window ledge for lack of any other available flat space, were slim cylindrical cores of glass, lead, silver and of course, gold. There they caught the sunlight, bent it and released it again until patterns appeared on the far wall like waves on an ocean.

On this morning, when Daniel really ought to have been in class, they took each substance and, like some philosophical Noah, placed them two by two in the boxes and swung them back and forth like pendulums: first wood and wheat, then wood and sand, and on and on until each had been compared with the next. All the while, Isaac sat hunched like gargoyle over his notebook, timing each swing.

Daniel had been, grudgingly, allowed to handle the swinging itself, and even that was due largely to the great cosmic oversight which had allowed Isaac Newton to be born with only two hands and not six or seven. As it was, he was allowed to raise the two boxes to an equal height and release them at precisely the same moment, and then listen patiently as Isaac explained what he had done wrong.

And so the morning progressed into afternoon and evening and when Daniel went to bed that night, it was to the sound of Isaac's pen scratching out calculations nearby: M1 over M2 equals...

It would be years before Daniel understood fully the importance of that early spring morning, before it would become more than one of those formless notions that grabbed hold of Isaac so regularly, always part madness and part brilliance. It would be more years still before Daniel would look back and see trouble already taking root, for when he had ask Isaac, half in jest, "Would you like a measure of mercury as well?," Isaac had replied blankly, as if the answer should have been apparent, "What use is measuring a bible to find the weight of faith?"