![]() This is Antonini's drawing of Drebbel's "perpetuum mobile", when describing it to Galileo in a letter. Paraphrasing the description, we see a sealed sphere in the center, around which is a glass tube e-f (this corresponds to C-C in Tymme's illustration). The tube is open to the inside of the sphere using the tube D. The other side of the tube is open to the outside air, at c. The fluid in the tube, A-B, is therefore displaced towards B when the air in the sphere expands, and retreats toward A when it contracts. From what I gather... and this is an assumption on my part... this would cause the sphere and ring assembly to tip, due to the weight imbalance caused by the shifting water. But whether or not this would set up a rocking motion, or simply find a new balance and stay there until the next change, I was not sure. So I wanted to build one, and test it out. |
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![]() The sphere I used is a 10" diameter glass ball. The tube is sealed, via the white "cap", so that no air can go into or out of the sphere except through the tube. The axles, epoxied to the sphere, are small steel pins which afford limited friction. The liquid is dyed water. I first balanced the device so that it would just barely sit at rest in an upright position. I did this so that any shift in the water would cause a weight shift sufficient to rotate the sphere on it's pivot. It works! Well so far, the sphere moves to new positions according to the relative pressure of the air in the sphere to the air in the room. I gently warmed the sphere with a hair dryer... at such a setting and position that the air flow from the dryer had no effect on the sphere. This is of course "cheating", and only to demonstrate the action in a more immediate way. As it warmed, however, the water moved (to the right in this picture), and the sphere rotated clockwise. When I took away the dryer, and the sphere was allowed to cool for a few minutes, the sphere rotated back to the position shown. |
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![]() From this picture we learn several things. First of all, we can see what an extraordinary glass worker Drebbel was. To make a tube like this, so perfectly round, would have been quite a feat at a time when most blown glassware was very uneven, and inconsistent. There is a base on this unit. There is another version of the same scene in the Prado, which does not have the person to the left. In that shot, there is a device of some kind, linked to the base somehow. It appears to have metal or glass tubes, tilted to face the sun coming in the window. I believe something may be in that base, but cannot be sure. Also, we have a clue as to the way the indicators worked. There appears to be separate brass disks, possibly representing the sun and planets, in the center of the sphere. I believe the clock drive may have been in a chamber in the sphere, but separated from the inner pressure chamber. |
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![]() Here is the model with the fluid portion only. As such it is only a barometer/thermometer. I've been observing the rate and amount of movement of the fluid (water with food coloring). This will help me to determne if some of the ideas I've had for possible spring winding mechanisms will work, and also to help think of other ways this might have been done. The simplist would be a floating glass ball in the "internal side" of the tube, with a thread running over a pulley to a weight inside the sphere. The float would be just light enough to not sink, and the weight would be just less than that. then the thread would run around another pulley in the sphere, and as the water rose and dropped, it would turn this pulley to and fro. This then would be connected to ratchets and a shaft, so that either way it moved, it would wind a spring in one direction... and so, drive the clock. There are several more complicated methods I have in mind, all of which would have been obvious to Drebbel, and would use methods known to his time and place. |
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![]() This is the first "new" image of a Drebbel perpetuum to surface in (probably) centuries. It is from the mysterious painting known as the "Linder Gallery", which is the subject of an excellent book by Michael Gorman, A Mysterious Masterpiece: The World of the Linder Gallery. The painting is in the Ron Cordover collection, and there is an excellent site about the painting, and some analysis of it, here. When I had first heard of this image, I had tried very hard to find an image of it... hoping, in fact, to get a viewing of it. I had also hoped that the image would further my understanding of these devices. I only recently decided to try again to see it... and found that it is now online. I was lucky in that the owners of the painting had allowed it to be posted online, but still hope to contact them and see it in person... Although it is a dark and shadowy image, perhaps seeing the device up close will reveal something not seen in the web image. Even a certain brush stroke in a certain way, could very well reveal a valuable detail. For one thing, if the main sphere is at all rotated from "centered" in the glass tube, it would mean that this was in fact a rotating part. The Walters and Prado examples both show the sphere "straight ahead". And here is a blog post, which discusses the Linder perpetuum in context. I do personally wonder if the fact that Drebbel's device is in the shadow of the painting is not meant to be symbolic of his approach to "science as magic", which did annoy those trying to bring science out into the light of reason. Drebbel used science to perform "tricks", hiding the true operation so as to best sell them, and himself. The artist, and the collection representing this, seems to reject this... the positioning of Drebbel's famous device in the dark may then be a visual rejection of this attitude. |
![]() This is an engraving of the clock in it's entirety, from Thomas Tymme's 1612 Dialogue Philosophicall. This elaborate model was made for King James I. What are the odds that bits of it are crated away in a London basement? Tymme's description stated that "A", the globe, represented the Earth, "C-C" was the glass tube, with water in it, to represent the movement of the tides, and "B" was a rotating model of the phases of the moon. He also states there was a clockwork in "A", and that the movement was so slow so as to limit wear on the parts. From this and other descriptions, it seems to me... purposefully or not... that the daily variations of air pressure was being confused with the cycle of the tides. This because the fluid in C-C would only be affected by the pressure in A, and not by the moon's gravity (of course). Then Drebbel somehow used the level in C-C, or the changing pressure of the air above it, to rotate the moon phase indicator at B. So the question is: Did Drebbel make a mistake in associating daily fluctuations in barometric pressure with tides, or only sell his clocks as doing so, while knowing the truth of the matter? I wonder at the clockworks, too, after reading the description. I have to wonder if there was some very simple method in this, of marking the rotational movement of the globe, without a complicated works. Like the pointers simply being nudged around the ring somehow. Until I find more descriptions, and play with my version a bit more, I can't know for sure. |
![]() Here is a blow up of the clock from the Tymme engraving. Although Tymme stated that C-C is the outer "crystal ring", I suspect that he is actually referring to the ring just inside, as it appears to be a glass tube, and connected to the cross-piece from C to C (c to shining c?). The outer ring appears decorated, and solid, in this drawing. A is described as the globe, which is marked in twenty four hour increments. Both Tymme and Drebbel state that this rotates, and Tymme states it had a clockwork built in. For these reasons, and it's small size, I suspect this is not the sealed air chamber as in the version in the Antonini sketch. I am tending toward the belief that the air chamber is actually in the base of this clock, which is unusually large in relation to the works. Looking closely at the engraving, other important details come to light. For one thing, in the outside glass tube, just below the place the cross tube joins it on the left, you will see what appears to be a water level. The small tube above the inner ring, and attached to it, has two marks on it. Just above the lower mark there appears, faintly, a ball. My guess is this is the filler neck to replenish the water, and the ball and lines are a filler gauge. Periesc asked a friend, whom he insisted should see this very clock, to ask the attendants how often the water needed replenishing. Another feature is the center man. He appears to be a decorative support, perhaps for the globe's axle, and maybe the cross tube also. It seems the seraphim were to support the outer (metal?) ring, and the man the axle and glass. Perhaps, if the air chamber was in the base, a tube also ran up the man to the mechanism. I wanted to study the existing sketch and descriptions, and make a CAD model of the clock, in order to better understand how it might have worked. To start, though: as I said on the Drebbel page, this clock, or at least it's motor, was basically a mechanical barometer. As such, it would not have been able to sense or indicate the tides. So if this was a claim of Drebbel's, he was either being dishonest, misunderstood, or in error. I tend not to believe the latter, as the man did certainly understand that the force acting on his circular column of water was the difference in relative pressure between his sealed chamber, and the outside air. |
![]() While making the CAD model, I felt accuracy was very important. Although Tymme's written description is agonizingly incomplete, the artist who engraved the clock seemed to take pains to include much technical detail. I felt they likewise must have cared about proportion, and proportion is the make or break of this technology... the relative size of chambers and tubes, the angle of moments which would affect the effort exerted on the axle, etc. To keep it accurate to the drawing, I textured a plane with the actual engraving, and built the clock on that. |
![]() One possibility occurred to me as I was researching this clock. I came across Kircher's Clock, which also used a smaller globe to tell the time. Kircher's globe was also marked in 24 hour increments, but it floated or hung in a globe of water, with a fish model as an indicator. The claimed operation was that the globe was remaining still, while the Earth and the clock rotated under it. The problem? It was a trick! Kircher had a water clock hidden in the base, which turned the globe via magnetic traction. Not to impugn Drebbel, but I wonder if his machine was part reality, in the barometric action part, but a parlor trick in the rotating globe part. This would be an especially strong possibility if the glass tubes did not move in this clock. Kircher's clock relied on an attendant secretly replenishing the water of the water clock in the base when no one was looking... Drebbel's clock, if powered the same way, would have had the advantage of allowing a fill in front of the awed onlookers! A small amount could have run down a tube, into the base, and run a water clock. This could have driven the globe easily via a small shaft through the body of the man sculpture. Again, I don't want to second guess Drebbel on this, but only want to point out what is a practical, technical and historic possibility... as one option. |
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