Dear dail-list-ists, I visited Cabrillo National Monument Saturday and talked with Ranger George about the Spanish attempts to finish what Columbus started. I am full of questions but feel sure that some of you can help me. For decades after Spanish colonies had been established in Mexico, they still believed the Pacific was only a third as big as it is. I don't understand this. Of course, finding the longitude for purposes of navigation is tough because the accuracy required is high and the conditions are terrible, i.e., a rocking surface that is not in the same place for any two observations, the need for a good fix greatest when the observing conditions are worst, and no access to libraries of reference material and mathematically-minded consultants. But how can it be that hard to determine the longitude of, say, Mexico City with an accuracy of at least 10 degrees, even given only 16th century technology? I would imagine sending a couple grad students over to record the time of day (night) that various stars disappear and reappear behind the moon, sending the tables back to Spain where similar observations were made, and setting the brightest mathematical minds of the empire to work comparing the two sets of observations to come up with a fix on the longitude. Apparently something similar was eventually done using a lunar eclipse, but the result was still off by 25 degrees. A lunar eclipse is a rather sluggish event. Is this really a better method than occultations? Was the final error due to poor observations or poor theory, or is that the inherent accuracy of the method? Ranger George seemed to think that the expectations that the Earth was smaller greatly inhibited the discovery of the actual size. The ancient Greeks had believed in a rather small value, and who could question their authority? It was also an important point of theology at that time that the Gospel had spread to all mankind, so the Americas logically had to be connected by land to Asia. I have trouble believing that hard-headed economic interest in knowing the truth would not win out over these prejudices, but then, I am definitely a child of my age. Knowing where Mexico is is only half the problem, but finding the longitude of Asia could be solved by the same method, unless the Spanish did not have a presence there. When did the first European ship reach Asia? The first Spanish ship? Was it sailing from the West or the East? Was Magellan's fleet the first to cross the Pacific or only the first to accomplish a circumnavigation in one piece? Thanks for any elucidations.
--Art Carlson
