At the end of the fifth century, celestial navigation was just being developed in Europe, primarily by the Portuguese. Prior to the development of celestial navigation, sailors navigated by "deduced" (or "dead") reckoning, hereafter called DR. This was the method used by Columbus and most other sailors of his era. In DR, the navigator finds his position by measuring the course and distance he has sailed from some known point. Starting from a known point, such as a port, the navigator measures out his course and distance from that point on a chart, pricking the chart with a pin to mark the new position. Each day’ s ending position would be the starting point for the next day’s course-and-distance measurement.
41._______________________.
The ship’s speed was measured by throwing a piece of flotsam over the side of the ship. There were two marks on the ship’s rail a measured distance apart. When the flotsam passed the forward mark, the pilot would start a quick chant, and when it passed the aft mark, the pilot would stop chanting. The pilot would note the last syllable reached in the chant, and he had a mnemonic that would convert that syllable into a speed in miles per hour. This method would not work when the ship was moving very slowly, since the chant would nm to the end before the flotsam had reached the aft mark.
42.____________________.
Columbus was the first sailor (that we know of) who kept a detailed log of his voyages, but only the log of the first voyage survives in any detail. It is by these records that we know how Columbus navigated, and how we know that he was primarily a DR navigator.
43.___________________. If Columbus had been a celestial navigator, we would expect to see continuous records of celestial observations; but Columbus’s log does not show such records during either of the transatlantic portions of the first voyage.
It has been supposed by some scholars that Columbus was a celestial navigator anyway, and was using unrecorded celestial checks on his latitude as he sailed west on his first voyage. 44.______________________ In other words, if Columbus were a celestial navigator, we would expect to see a sense of small intermittent course corrections in order to stay at a celestially determined latitude. These corrections should occur about every three or four days, perhaps more often.
But that is not what the log shows. 45.________________. Only three times does Columbus depart from this course: once because of contrary winds, and twice to chase false signs of land southwest. In none of these cases does he show any desire to return to a celestially-determined latitude . This argument is a killer for the celestial hypothesis.
[A] Since DR is dependent upon continuous measurements of course and distance sailed, we should expect that any log kept by a DR navigator would have these records; and this is exactly what Columbus’s log looks like.
[B] On his return voyage in 1493, Columbus started from Samaria Bay on the north coast of Hispaniola, and he made landfall at Santa Maria Island in the Azores. We know his entire DR courses and distances between these two points, since they’re recorded in his log.
[C] In order for this method to work, the navigator needs a way to measure his course, and a way to measure the distance sailed. Course was measured by a magnetic compass. Distance was determined by a time and speed calculation: the navigator multiplied the speed of the vessel (in miles per hour) by the time traveled to get the distance.
[D] On the first voyage westbound, Columbus sticks doggedly to his magnetic westward course for weeks at a time.
[E] Could Columbus has corrected his compasses by checking them against the stars and thus avoids the need for course corrections This would have been possible in theory, but we know that Columbus could not have actually done this.
[F] Speed (and distance) was measured every hour. The officer of the watch would keep track of the speed and course sailed every hour by using a peg-board with holes radiating from the center along every point of the compass. The peg was moved from the center along the course traveled, for the distance made during that hour. After four hours, another peg was used to represent the distance made good in leagues during the whole watch. At the end of the day, the total distance and course for the day was transferred to the chart.
[G] In that case, as magnetic variation pulled his course southward from true west, he would have noticed the discrepancy from his celestial observations, and he would have corrected it.

41（）

At the end of the fifth century, celestial navigation was just being developed in Europe, primarily by the Portuguese. Prior to the development of celestial navigation, sailors navigated by "deduced" (or "dead") reckoning, hereafter called DR. This was the method used by Columbus and most other sailors of his era. In DR, the navigator finds his position by measuring the course and distance he has sailed from some known point. Starting from a known point, such as a port, the navigator measures out his course and distance from that point on a chart, pricking the chart with a pin to mark the new position. Each day’ s ending position would be the starting point for the next day’s course-and-distance measurement.
41._______________________.
The ship’s speed was measured by throwing a piece of flotsam over the side of the ship. There were two marks on the ship’s rail a measured distance apart. When the flotsam passed the forward mark, the pilot would start a quick chant, and when it passed the aft mark, the pilot would stop chanting. The pilot would note the last syllable reached in the chant, and he had a mnemonic that would convert that syllable into a speed in miles per hour. This method would not work when the ship was moving very slowly, since the chant would nm to the end before the flotsam had reached the aft mark.
42.____________________.
Columbus was the first sailor (that we know of) who kept a detailed log of his voyages, but only the log of the first voyage survives in any detail. It is by these records that we know how Columbus navigated, and how we know that he was primarily a DR navigator.
43.___________________. If Columbus had been a celestial navigator, we would expect to see continuous records of celestial observations; but Columbus’s log does not show such records during either of the transatlantic portions of the first voyage.
It has been supposed by some scholars that Columbus was a celestial navigator anyway, and was using unrecorded celestial checks on his latitude as he sailed west on his first voyage. 44.______________________ In other words, if Columbus were a celestial navigator, we would expect to see a sense of small intermittent course corrections in order to stay at a celestially determined latitude. These corrections should occur about every three or four days, perhaps more often.
But that is not what the log shows. 45.________________. Only three times does Columbus depart from this course: once because of contrary winds, and twice to chase false signs of land southwest. In none of these cases does he show any desire to return to a celestially-determined latitude . This argument is a killer for the celestial hypothesis.
[A] Since DR is dependent upon continuous measurements of course and distance sailed, we should expect that any log kept by a DR navigator would have these records; and this is exactly what Columbus’s log looks like.
[B] On his return voyage in 1493, Columbus started from Samaria Bay on the north coast of Hispaniola, and he made landfall at Santa Maria Island in the Azores. We know his entire DR courses and distances between these two points, since they’re recorded in his log.
[C] In order for this method to work, the navigator needs a way to measure his course, and a way to measure the distance sailed. Course was measured by a magnetic compass. Distance was determined by a time and speed calculation: the navigator multiplied the speed of the vessel (in miles per hour) by the time traveled to get the distance.
[D] On the first voyage westbound, Columbus sticks doggedly to his magnetic westward course for weeks at a time.
[E] Could Columbus has corrected his compasses by checking them against the stars and thus avoids the need for course corrections This would have been possible in theory, but we know that Columbus could not have actually done this.
[F] Speed (and distance) was measured every hour. The officer of the watch would keep track of the speed and course sailed every hour by using a peg-board with holes radiating from the center along every point of the compass. The peg was moved from the center along the course traveled, for the distance made during that hour. After four hours, another peg was used to represent the distance made good in leagues during the whole watch. At the end of the day, the total distance and course for the day was transferred to the chart.
[G] In that case, as magnetic variation pulled his course southward from true west, he would have noticed the discrepancy from his celestial observations, and he would have corrected it.