Gershom Bradford II

“ It is here particularly shown that navigation becomes an art of estimating position and the better the navigator’s bump of locality, the greater his success. This is a peculiar gift and usually is born in the man, at least it cannot be learned from books. The process of finding latitude and longitude by dead reckoning is supposed to be already well known to the reader and will not be detailed at length. ”

“ In practical navigation a vessel commences her voyage and attempts to sail in a certain direction, but the well-known elements of compass error, variation and deviation, current, wind, seas and poor steering all divert the vessel from the projected course. In dead reckoning a navigator strives to keep track of his position by keeping a record of actual courses steered and distances run. ”

“ Middle latitude sailing is very similar to parallel sailing in that it is assumed, for the purpose of getting the difference of longitude, that the whole departure of the course or courses sailed has been made in the mean or middle latitude, because the greater value (in the northern hemisphere) in difference of longitude of a mile northward of the middle latitude is counteracted by the corresponding lesser value southward of the middle latitude. ”