They went on to others as the schooner rose and fell on the long swells, and the sails hung listless as parlor drapes and the booms swung with the creaky, banging racket that is the sound of a becalmed vessel. To find one’s actual position, Will lectured, you must first plot an assumed position, that is, where you think you are. Generally, the assumed position is taken from dead reckoning. You then make six visits to the Nautical Almanac and three to the Reduction Tables, and after doing twenty-one computations, plot your line of position by comparing the sextant reading at the time of the sight to the assumed position’s sextant reading.

Will led his pupil through the painstaking process, and the experience was like being in a dark room divided by numerous curtains of diminishing thickness. At first, all was opaque; then the first curtain rose and he saw a faint, faint light. Up went the next curtain, and the light grew a little brighter. He grappled with Greenwich hour angle, which was the same as a heavenly body’s longitude, and with local hour angle; with declination, dip corrections, refraction corrections, and other mysteries. He concentrated mightily and felt that his brain would suffer muscle strain in its efforts to lift all the curtains and bring the mysteries into the full radiance of comprehension.