Pagee 159

…therefore, with certainty, that his ship at noon was at that exact spot, on the chart where the 73rd meridian of W. long. crossed the 40th parallel of N. lat., because he is on both at once, and can be nowhere except at their intersection. (page 146). If his position happened to come in odd minutes instead of even degrees, he could find the place with a little measuring.

This, as you've read it, gives the theory and the actual practice in its simplest form. The real operation of "working out a sight" is not so easy, as what you've read, for there are many allowances and conditions to understand and figure out.

But with experience, skill, care and knowledge, and with a sky that will allow him frequent sights at the sun or the stars – for the stars are also used, a captain can take his steamer across the ocean as accurately as you can stear a bicycle across a park, and he can keep in the center of a narrow “steamship lane” as exactly as you can keep your wheel to the center of the gravel walk. Finis