Letter from Charles S. Peirce to Carlile P. Patterson [II]
(Richmond, 06.07.1876)



 
Spanish translation & annotations
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Richmond, 1876 July 6

C. P. Patterson Esq.

Supt. U. S. Coast Survey

Washington D. C.

 

Dear Sir,

I have now a large amount of information relating to my work to report to you but I have not at present the time to draw up a regular report of it. I therefore beg leave as I find the time to write to you upon detached points.

My pendulum work in Europe is now nearly completed and the experiments have been increasing in accuracy from station to station. Here they must be the most accurate I have yet made. This is partly owing to my increasing understanding of the subject and partly to accident. Two of the most difficult conditions of such work are steadiness of the support and steadiness of the temperature. In regard to the former, I have devised a method for

 
testing it. (This is quite a different matter from the stiffness of the stand, which I have also devised a method for measuring.) I make use of the microscope of my comparator which I use in measuring the pendulum. I set up before it a scale which rests upon a long lever which is turned by any yielding of the support and then I apply a force to the support tending to move it. In this way I have obtained results which have surprized everybody who has seen them. I have tried some very heavy stone vaulting but have found none which was not unsteady.

In Geneva, the floor was an asphalt one & the pendulum had to rest on that. People constantly came in and out & it was as bad as possible. The temperature conditions were also excessively bad, the room being a small one with glass doors on both sides, leading into the open air, and these doors were frequently opened in. But the shining in of the sun was still worse in its effect. The consequence is that the pendulum results at Geneva, although satisfactory are not particularly good.

In Paris, I swung in the great Salle du Méridien where several observers have already swung. The others

 
swung at the south end but I preferred the north end. Here, the temperature was really extremely constant and there was plenty of light, an important condition. But the pendulum rested on the floor which was tiled & which yielded extremely easily. I am not yet able to say whether this has vitiated the results mucho or not. But they must be considerably better than at Geneva.

In Berlin, the pendulum rested on an independent pier and was absolutely steady. But the chamber of which I must write at length on another occasion had no windows & a most complicated system of lenses and mirrors had to be devised & made in order to give me the requisite light which was thrown from distant lamps placed in flues. The effect of these spots of light upon the temperature was excessively bad. Still I made every effort to reduce it and undertook a second independent series of experiments on another plan to avoid the effect, & I am therefore confident that the results from this station will be considerably better than those in Paris.

In Kew, both the temperature & steadiness are very good,

 

 
the light only is extremely troublesome. But the results so far as I have ascertained them seem to manifest an extraordinary degree of agreement. I shall be obliged to bring my experiments here to a close sooner that I should desire but still I hope they may be the best I have yet made.

I have made during the year various improvements in the art of swinging pendulums. The most important is my measurement of the flexure of the stand, which introduces a very large correction into all results with the Repsold reversible pendulums. General Baeyer, who is really the head of European geodesy, was extremely pleased with this and brought a large party of scientific men to see my apparatus in operation in Berlin.

However, the invention which pleases me the most is a new method of noting the time of vibration which will greatly diminish the expense of computations which is excessive on my present system. In this new method, there is a little lever of aluminium AB turning upon a fine steel axis C. There is a third arm with a little ball D which moves the centre of gravity

This is above the fulcrum so that the pendulum will rest with either end down. It is prevented from turning

 

 

 
completely over by hitting upon two screws E and F. At G is a little cup of mercury which can be adjusted by a screw so that a platinum wire depending from B will enter the mercury when the end B is down & will be out of the mercury when the end A is down. At A is a little agate. The pendulum as it passes the vertical position strikes A & turns the lever so that it rests with the end A down. Now in regard to this matter two precautions have to be observed. First, the lever is so adjusted on an arm with two motions that the break occurs when the pendulum is as nearly as possible vertical. Now it is a proposition of mechanics that no resistance to the motion of a pendulum while it is in the vertical position can affect the time of oscillation but only the amplitude of the arc. Second, the agate A is struck by a little piece of mica attached at the level of the lower knife edge, for it is another proposition of mechanics that attaching a weight to the pendulum at that point has no effect on the time of oscillation. When the lever has been thus turned it remains with the end A down. But at H there is a little cross piece of steel & under it a little electromagnet & when a current is passed through this magnet, the lever is turned back so that the end B

 
is down. There is also a galvanic connection through the fulcrum & the lever & the mercury at G so that the connection is made when the end B is down and broken when the end A is down. Having this automatic contact breaker and my break circuit chronometer, the idea of my new method, is to register the interval of time between the passage of the pendulum across the contact breaker & the next second of the chronometer to thousandths of a second upon a Hipp's Chronoscope. A Hipp’s chronoscope measures the interval of time between the breaking of an electric current & its permanent remaking & registers it on a dial so it can be instantly read. Its probable error, after applying to it an important correction which I have discovered, is only about 2 thousandths of a second. It is true that the break-circuit chronometer only breaks for a small fraction of a second & the Hipps chronoscope requires the second signal to be a permanent make. But I avoid this difficulty by a peculiar arrangement of a relay and the effect is as follows. At first, the end A is down & the pendulum swings freely. The observer presses a telegraph key and at the same time looks at the chronometer & notes the time. He keeps his hand on the key for 20 ½ seconds. During this time the lever is first turned over so that the end B is down, when the

 
little electromagnet at H ceases instantly to act and the lever is free to be turned back as soon as the pendulum passes. The pendulum passes & the lever turns & the circuit through G is broken  and the Hipp chronoscope hand begins to move. As soon as the chronometer breaks again the Hipp chronoscope hand is stopped & also the electromagnet at H acts & turns the lever so that the circuit is made through G. As soon as the circuit is made through G another circuit is broken so that the chronoscope will move forward again at the next break. This repeats itself as long as the hand is kept on the telegraph key. At the end of the 20 ½ seconds, the hand is removed from the key and the next passage of the pendulum turns the lever without moving the chronoscope & all action stops. The chronoscope is now read. And the reading being divided by 10 gives the interval between the middle passage of the pendulum and the next chronometer second, quite accurately to a thousandth of a second.

I do not trouble you with the arrangement of relays by which all this is effected.

An observation of this sort can be made by one person & the result can be obtained in a very short time, whereas at present two persons are needed to make the observations and

 

 
the result cannot be known until 800 chronograph records have been measured up for each experiment.

I was very desirous of using this method in Berlin where it would have been peculiarly advantageous, owing to its not requiring much light, but Tiede the great  watchmaker there kept me waiting nearly a month for the contact breaker, promising it from day to day & then did not make it as I wished, so that afterwards I ordered it made of Breguet. I expect to have it very soon and if any more pendulum experiments have to be made after Farquhar leaves I shall make use of this method.

Yours very respectfully & truly,

C. S. Peirce
Asst.

 

 

Transcription by Max Fisch, revised by Sara Barrena (2014)
Una de las ventajas de los textos en formato electrónico respecto de los textos impresos es que pueden corregirse con gran facilidad mediante la colaboración activa de los lectores que adviertan erratas, errores o simplemente mejores transcripciones. En este sentido agradeceríamos que se enviaran todas las sugerencias y correcciones a sbarrena@unav.es
Proyecto de investigación "Charles S. Peirce en Europa (1875-76): comunidad científica y correspondencia" (MCI: FFI2011-24340)

Fecha del documento: 29 de septiembre 2014
Última actualización: 29 de septiembre 2014
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