[D8905AEN], Letter from U.S. Navy Dept. Bureau of Navigation, David Peck Todd to Thomas Alva Edison, July 20th, 1889


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[D8905AEN], Letter from U.S. Navy Dept. Bureau of Navigation, David Peck Todd to Thomas Alva Edison, July 20th, 1889

Editor's Notes

[TAE marg: Kennely what about this?] The Navy Department has appointed me to the charge of the Eclipse Expedition to West Africa, and there will be exceptionally favorable circumstances for utilizing the apparatus for getting valuable observations at sea, as referred to in my letter to you last November. One of the new naval cruisers--the YORKTOWN or the BALTIMORE--will carry the party out & bring them back. New vessels have, or will have, Edison Lighting plants, & the dynamos being already in position, a large item of expense of the experiment will be provided for. The party will sail from New York about October 1st. ## I have made all the necessary arrangements here and secured the permissino of the Department to test the apparatus experimentally on one of those vessels, & to utilize it off the African coast on eclipse day, Deccember 22nd. ## Now our eclipse appropriation is too small to admit of any expenditure for this work; and of ourse the Department cannot do any more than I have at ready indicated. From the rough drawing enclosed you can see, however, that the apparatus will not be very costly. ## Smyth, the late astromoner Royal for Scotland, says his first experiment was so successful that he kept the spider-line of his telescope bisecting the horizon line for a long time, notwithstanding large motions of the ship. ## I have read his printed acounts of the experiment, & in correspondence with him lately, I have got new suggestions. ## If the rerevolvers can be driven electrically, the thing must be a success. Will it not be possible to send the current through the set-screws at the ends of the revvolver-axles, & at the sides of the symbol-rings? ## I am quite ready to furnish further plans, & superintend construction & testing of the apparatus. It would be advantageous if it could be undertaken at once, as the BALTIMORE goes out on her next trial trip inside of a month probably. ## [DRAWING, followed by: Telescope or camera (I should use the latter in the coming eclipse, for getting long-exposure photograph of the camera in the outer regions, where absolute definition is not very important) is mounted on a little table fastened to a spindle running by frictionless bearing through the main frame. Spindle terminates below in a symbol ring with a piot at bottom. Inside this ring is a horizontal symbol ring pivoted at sides & shown only in Section. Inside this ring is a gyroscope revolver, turning in a vertical plane, axis of which is shown as the central point. Lower portion of main frame contains a much larger revolver, turning in horizontal plane. Pivot screws in same plane allow swinging of the whole apparatus bak & forth., There screws go through a square frame, partly shown; & which is itself pivoted at right angles to the axis of other pivots, & swings between two vertical posts rigidly attached to the deck of the ship. Latter screws, posts &c. not shown, W W counterbalances the whole weight of the revolver, telescope, &c. Lower revolver at a high speed (say 80 to 100 turns per second) keeps the table absolutely horizontal---that is, it corrects for PITCHING & ROLLING of ship. Upper revvolver corrects for [AZIMUTH?], or change in her compass reading. If she lurches bodily to one side, the effect is nil, as the perfection of counterbalance by means of WW prevents all change of direction. The ship can have no other motions, no matter how rough the sea. Smyth recommends a revolver weighing 10 lbs. to control the position of a sextant or a small telescope. I think this would do for upper one, as the azimuth changes of the ship could be specially provided against by quartermaster of the venue at time of eclipse, so as to keep her course quite accurately. But lower revolver should be at least 15 lbs. I should say, as her rolling & pitching might be great. I think George Clark would be a first rate man to work on the revolvers, as he has been through the mill with the revolving mirrors of Prof Newcombs velocity-of-light apparatus. These he got into fine shape, running up to 200 per second, & perfectly smoothly & without a particle of jar. Of course the critial point of all is the application of the electric motive power. It should be in opposite directions on opposite sides of the axles, so as to reliee strain on pivots. I assume of course that you are equal to the solution of that problem. D.P T Washington 89.07.21 P.S Of course the symbol frames should be as light & strong as possible--steel, perhaps. Revolvers would not probably need continuous application of power; but during total eclipse (3 m 30 s) they might be left spinning by themselves. It might even be advisable to box them in, in the inner symbol rings, & partially exhaust the air. Then of course it would not be material whether urrent were communicated through pivots or not. T [Name mentions: David Pek Todd US Navy Dept Bureau of Navigation Thos Edison Arthur Edwin Kennely George Clark Prof Newcombs Yorktown Baltimore Smyth, Royal astronomer for Scotland West Africa ]





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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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