Tag Archives: navigation

So what time is it anyway?

Tonight’s reading of Dava Sobel’s book ‘Longitude’ reminded me of one of my favorite great “difficulties” from history. Specifically, just how hard it has been throughout mankind’s existence to tell what exactly the time is. It is one of the most bedeviling of problems, since we live on a sphere and the motion of the sun and moon define the very concept of time for us. Unfortunately, twelve noon in New York looks exactly like twelve noon in New Delhi. The book’s topic is primarily that of determining longitude (obviously) but since this is so closely married to the more interesting problem of time-keeping, I felt it incumbent to tease out a few of the more interesting tidbits from tonight’s reading. It should be noted that I’ll only breeze over these points at the highest level. Anyone wanting to actually learn something should go read the book for themselves.

The book opens, and frames the problem of navigation with an ironic and grand story of misplaced wrath from 1707. A British naval officer is making his way home after a successful battle with a fleet of five ships on a very foggy evening. He is approached by a worried sailor who says his reckoning tells him that they are dangerously close to shore. The captain, offended by the affront, has the sailor hanged for mutiny. Minutes later, the entire fleet runs aground and the crews are almost entirely lost. With so few navigational aids, it was nearly impossible to be certain just how far east or west any ship might be. It all really boiled down to guesswork and even seasoned sailors were sometimes failures.

Galileo’s Celatone

One early attempt at solving this problem comes from Galileo. He noted rightly that the moons of Jupiter eclipsed and reappeared with amazing regularity. He constructed a device called a Celatone, combining a helmet and telescope, to aid sailors in observing the various movements of the moons. This, combined with a detailed table of expected movements would provide the time assuming that it was dark… and a clear night… and Jupiter also happened to be on the right side of the planet to be seen. Needless to say, this didn’t quite catch on. Somewhat relatedly, many years later a Danish astronomer, Ole Roemer, observed that the schedule of Jovian eclipses was inaccurate by several minutes depending on the relative positions of Jupiter and Earth in the solar system. He was able to use these deviations to make an exceptionally good calculation of the speed of light, which was thought at the time to be transmitted instantaneously.

Lastly for tonight, and most abundantly oddball, we have the story of “Sympathy Powder” from 1687. Sir Kenelm Digby is said to have discovered a “miraculous” powder that had the power of healing people at a distance. The only down side was that it was a rather unpleasant sensation when put in use. Using this miraculous concoction, the idea was advanced that a dog should be put aboard ship with a festering wound. Each day at 12:00 local time, the powder would be applied to some personal effect belonging to the dog, thus causing it to yelp and alerting the ship’s crew to the real time back home. Issues with this approach abound, of course, but it is a little known fact that this exact method of timekeeping is widely in use today. It is precisely this form of chronology that Doctor’s use to know when appointments are to be kept, at least if my own personal experiences with their promptness are any indication.

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