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Email This Page to a FriendPreview: Early Navigation Instruments, by Jim Sharp at the Sail, Power & Steam Museum
July 14, 2016
Schoonerman Captain Jim Sharp takes us on a tour of early navigation instruments through the ages he has collected at his Sail, Power and Steam Museum. Ever wonder how a cross staff, astrolabe, or latitude hook works? Well, here's your chance to find out about the early navigation instruments that preceded the modern sextant and more.
– [Narrator] Captain Jim Sharp, the long-time skipper of the schooner, Adventure, has cut a larger-than-life swaff down the Maine coast for five decades. As a schoonerman, waterfront developer, and epic storyteller, his pursuits are legendary and his friends are countless. Now in his 80s, Jim has turned his energies to a maritime museum, featuring artifacts that he and his many friends and colleagues have collected for decades. The Sail, Power & Steam Museum in Rockland, Maine is one of our favorite, hidden, off-center places to visit. Sit back and enjoy as Jim takes you through the development of navigation tools over the last 2,000 years. This is just one small exhibit at his very cool museum.
– We have a great navigation station, a lot of charts in here. Benefactor, Captain Flynn, gave us all of these navigational instruments here, a whole lot of different sextons that we have there for determining latitude and longitude. The world is split up in latitude and longitude. Latitude is just like the equator if that was the equator across there. That is one piece of latitude and from there to the North Pole, you have all the different degrees. It’s 90 degrees because, of course, it’s the right angle from there to there. 90 degrees til you get to the North Pole, but it’s all equal segments all the way across like that. Where longitude is pieces of a pie, you see. It runs from pole to pole and it comes out in segments, and each of those segments, of course, is a certain number of degrees, a certain number of miles as well. If you can imagine here you are at the equator, and the distance between that longitude line and that longitude line is quite wide and quite big, but by the time you get to the North Pole, they’re all coming together, and you can see they’re getting smaller and smaller and smaller. They understood latitude a hundred years before Christ. Latitude was so easy to get because you could look at the North Star. Just take that North Star at twilight and look at the horizon, and immediately you know in the Northern half of the world, you know what your latitude is. You can obtain latitude if you had a celestial instrument to determine the heighth of the sun above the horizon, the elevation on the sun in degrees. 150 BC, they were able to determine latitude from an astrolabe-induced celestial navigation with it and then down through the ages, here’s the way it advanced. First came a latitude hook or kamal, and it was one of my favorites. This is a very early instrument. This was back way before Columbus back in the 12, 1300’s. It used to come out through the Pillars of Hercules out of the Mediterranean, and when they would get out on to the entrance there, out into the ocean, they’d look up here and they’d get the North Star right there, and they would put the horizon down here, and they would haul this back and they’d tie a knot right next to their eye, and this captured their latitude. So they would go up to the northern part of Europe to another seaport. They would trade cargo up there, do the same thing, get a knot there. Then when they would come back to the Mediterranean, you never wanted to lay around the mouth of the Mediterranean very much ’cause they were Arab dhows there and they were very swift vessels, and they would plunder vessel coming in. They knew they were full of cargo. They would plunder them coming into the Mediterranean so you wanted to be at the right place so you would stand off-shore to, and then you would get this, get the North Star here and the horizon down here. If the North Star was down there, you’d have to go further north. If the North Star’s up here, you go further south until you get it right on that spot with this knot behind your eye, and you could turn east and go right directly into the Mediterranean as fast as you could. This’s a quadrant, same idea, except this uses gravity on it’s vernier scale here. You would peep through here at the solar body and you would be able to tell its altitude from the way that stays. Cross-staff is the same sort of thing. You’re doing the same thing. You take this and you hold this up against your face right here and you get the star or the sun there, and the horizon down here and you can adjust this until it is right in at the right place and that does the same thing for you. It tells you what the altitude is. The problem with it is you’re looking directly into the rays of the sun. You’re holding this thing up and the vessel’s moving back and forth, and one minute the sun’s behind your fist. The next minute you’re getting it full in the face. And a man named Davis came along in the late 1600’s. He invented a back-staff. This is a back-staff. Look at this crazy looking instrument, great big wooden thing, but it was an amazing advancement in navigation. You take a back-staff and you would hold it up and you’d sight it to the horizon with the sun behind you, and the sun’s rays would come over your shoulder casting a shadow on the vernier scale here and you could tell its altitude without looking directly into the sun. That was an amazing advancement in navigation at the time. And for a hundred years all through the 1700’s, this was the weapon of choice. Then Isaac Newton invented the split-image. He had a set of mirrors in an octant like that and the mirrors, of course, did the job of bringing the star to the horizon so you could see them both at the same time with the split-image very soon after that. The sexton, the common sexton was invented and developed. On this sexton, these two little nobbies here, you squeeze them together, and you can move that arc back and forth quite fast. So you can move that arc back and set it to zero.
– [Narrator] ‘kay.
– [Jim] There ya go. Now, of course, you wanna peep through those glass, peep through the telescope.
– And I’m gonna sight the North Star.
– Point at the North Star.
– You have that in your scope?
– Yep. And you see there’s sort of a double image there?
– Well, you want to keep your eye on the lower one. Now you want to squeeze those nobbies together and move that arc ahead very, very little, just enough so that you split the image. There, now you see the lower one? Yeah?
– Bring it down with… That’s the way, move it ahead and you keep coming down the wall with it. Oh, I think you’ve lost it, haven’t you?
– I have. I’ve got it right there.
– Now keep coming down with your sexton. Lower your sexton and keep that in, there you go.
– [Eric] Oh, I see, lower my sexton.
– [Jim] Lower the sexton and move the arc. There you go.
– [Eric] So it split the image.
– [Jim] Down til you see the horizon. See the horizon there?
– [Eric] And stop at the horizon?
– [Jim] Stop at the horizon and try and lay that star just on the top of the horizon.
– [Eric] ‘kay, just the bottom of the star?
– [Jim] Yeah, right–
– [Eric] Right at the horizon line.
– [Jim] Right at the horizon. Now read your vernier scale.
– 44 degrees.
– 44 degrees, and our latitude here is 44 degrees, five minutes. When you move down to the horizon, your sexton is still recording that one in the beginning, that’s the zero mark.
– [Eric] Right.
– [Jim] When you get down to the horizon, you had done 44 degrees to that point, and that essentially is what latitude’s all about. Theof the 1700’s was longitude. For theof longitude, they lost thousands of vessels and thousands of lives. They knew the idea, but they didn’t have the technology. Back in those days, of course, the technology that they needed was time. Time originated from sundials and they had pretty sophisticated sundials in those days. They had compasses with them and all kinds of different doodads that went along with a sundial in those days. But boy, they were awful hard to read at night. So Galileo was sitting in church one time in Pisa, you know where the Leaning Tower is. Before the tower was leaning, he was in the cathedral in Pisa, and here was this great chandelier hanging from theon a 50-foot chain and had the window open. A puff of wind came in and started that chandelier going back and forth, the pendulum back and forth, and they shut the window and it continued going on. Galileo was mesmerized by this. He timed it with his own pulse and he realized they weren’t losing much momentum at all. They got this idea for a pendulum regulating a clock. Clocks in those days, you’d lose 20 minutes in an hour. They were terrible. So he got this idea. He made drawings of it. But he never made a prototype. It took Christiaan Huygens in 1657 to make a prototype of a pendulum. The first man to put a pendulum on a clock, oh, it was an amazing advancement in clock making. It regulated a clock so that you could almost tell time with it. The problem was his pendulum was made of metal, metal rod. In cold weather, the rod shrunk up. In warm weather, the rod stretched out. And it changed the regulation of the clock. So a man named Harrison, John Harrison, an amazing, amazing man, carpenter. His father was a carpenter, had no education. All he knew about was wood. He decided he would build a clock and he had great fascination for clocks. He invented the grid-iron pendulum, rods of different coefficients of expansion so that one offset the other and the thing had never changed its dimension. He could time his clocks out to within three seconds a month from now. Of course, you could use that for navigation. Three seconds a month was nothing. Then he came along and he invented the grasshopper escapement. This is a grasshopper esc… This is the thing that makes a clock go tick-tock, tick-tock, tick-tock, tick-tock. One bearing, lignum vitae, naturally-oiled bearing, lignum vitae is a naturally oiled wood. You never have to lubricate it. All these counterweights, almost friction-free. This whole thing sort of floated back and forth. No friction, it kept accurate time. He built clocks in the 1700’s. The entire clock made of lignum vitae. Never had to oil ’em, never had to service ’em, and they’re still running today. Here in the 1700’s, the early 1700’s, they lost six out of seven of the prime British fleet on the Scilly Islands because of one of longitude. The Admiral, he said, “Call all the captains together. “We’re in the fogin the English Channel. “Call all the captains together “and we’ll see where they think we are.” He’d laid out the chart. Of course, the Admiral says, “I think we are here.” And if you’re one of the captains of the other ships, you would never argue with an admiral. That’s a hanging offense. So they all said, “Well, yes, Admiral, you must be right. “That’s where we are.” So, of course, they continued on up through the fog of the Scilly Islands and went ashore, and they lost six out of the seven vessels. The seventh one, seeing all the other six there with the crew drowning and the vessels sinking, he turned away and he came back and told the story. So the Crown said I’ll give anybody that can build a clock to go to sea with, I’ll give 20,000 pounds. Now that was a fortune back in those days, 20,000 pounds. So John Harrison decided he would take on that challenge. He build this clock. In 1736, he finished it, 10 years of research and 10 years of building, and here’s this crazy clock. It’s all counterweights, crazy different counterweights with springs and everything else. It was four feet high, four feet long, and four feet wide, and it didn’t even look like a clock. The Crown looked at it and said, “Well, you’re gonna have to prove that to us.” So he did, and of course he experimented on all kinds of little vessels, made sure the thing was gonna work. They took it on a trip and they were coming up the English Channel and again got into an old fog, which they all, so frequently did over there and the captain had sense enough to come down and say, “Mr. Harrison, what does your clock say?” He says, “We’re 67 miles too far west. “It’ll put us right on the Scilly Islands.” They corrected their course and came right up the center of the English Channel. It worked, but they wouldn’t give him the money. They said, “It doesn’t look like a clock to us. “You gotta build something that looks more like a clock.” This thing took up most of the space in the cabin down below, you know. So he went to work and he built another one a little bit larger than that chronometer right there. And, it was a successful thing. They didn’t like it anyway. He built another one. He built five clocks before he was finished and the last one he built was the size of a large pocket watch. They went to the Caribbean on a six-months voyage, came back, and it lost 13 seconds. Then they decided, well, they gotta do something about this clock. It’s for real. So they took that clock, took it all apart and they made identical parts, one for each of the vessels of the British Admiralty and they put those clocks aboard. Then they finally decided that they would give him half the stipend. Then he was too old to even care. Then finally, posthumously, after he’d passed away they gave him the other half, but he invented the first chronometer and with the chronometer, they were able to tell time at sea and learn their position, learn their longitude.