|Spanish translation & annotations|
U. S. Coast Survey
Washington D. C.
At the end of last month I had found that it was proper to swing my pendulums at the Kew observatory, which is chiefly a magnetical establishment and belongs to the Royal Society but which has been made the initial point of all the pendulum work of British surveys. I found the director of the observatory disposed to assist my purposes. I found however that I could not swing there without certain formalities, and at the suggestion of Mr. Scott, the chairman of the Kew Committee of the Royal Society, I addressed a letter to Gen. Schenk, our minister, applying to him to ask the British Foreign office to request the Royal Society to direct that I should be allowed to swing my pendulums at Kew. I personally explained the matter to Gen.l Schenk and anticipate no difficulty in swinging there in the spring. A German traveller who has been swinging in Australia proposes to swing in Kew at some time and it is understood that we shall make some arrangement so as not to clash.
I saw at Kew the vacuum apparatus constructed under the direction of Captain Basevi and used by him (and after
his death by Capt. Heaviside) in all the pendulum work in India. I also saw the pendulums of Kater, Sabine, and Foster. And I saw the experiments of the officers of the Artic expedition actually in progress. I also saw the vacuum apparatus belonging to the observatory which I understand to be the same that was used by Baily.
The Kew vacuum apparatus is built up of successive cylinders of glass, the tops and bottoms of which are ground plane. They are simply put together with hog’s lard. It was said not to be very tight. I once considered making my apparatus in this way.
The Vacuum receiver of Captain Basevi is extremely tight, much better than mine in that respect. My leakage is almost wholly at the windows and his windows are constructed almost precisely like mine. The only difference is that in his there is a frame of four separate pieces of metal over the glass. It may be that these are screwed down so as to press the panes on with considerable force. I must have such plates fitted to my windows.
Basevi’s receiver is made of copper instead of iron as mine is. Apparently some magnetical effect was feared but of what kind I did not learn. I heard from the Repsolds that Sawitsch who at one time contemplated a vacuum chamber for the reversible pendulum feared that if made of iron there might be a magnetical effect on the knife-edges. This suggests as an easy precaution always setting up pendulums facing north and south. I think, however, the fear of using iron was rather a vague one. Perhaps it is wise however.
The top of Basevi’s receiver instead of being a metallic plate fastened on by bolts is simply a glass
bell put on to a brass collar at the top of the receiver, hog’s lard being interposed. I admired this plan greatly. The supports of the pendulum are quite above the plane of the collar and can be seen on all sides.
Basevi’s starting lever and also the one which raises the pendulum off the agates (which I do not have at all) are inserted in the side of the receiver so that they are not disturbed by taking off and putting on the cover.
Basevi has no frame which contains the whole apparatus within the receiver and which can be all taken out at once. In this respect I certainly have a better arrangement.
Basevi’s receiver instead of resting simply on feet is attached by a massive iron collar (he does not seem to have feared iron here) about the top to an immense wooden framework. I really can see no advantage in this. What seems to be feared is a flexure of the apparatus as the pendulum swings back and forth. If a great metallic cylinder –the receiver- is going to do this I believe that any wooden frame would do so. Professor Stokes said he had the impression it was originally intended to have two brick piers built at every station where the pendulum was swung.
All the pendulums at Kew except Captain Kater’s reversible pendulum were of one construction. There was a heavy bar of brass with a disk-shaped bob and a very long and large pointer. The knife-edges were however in several cases in quite a shocking condition.
Foster’s agates were not plane but were slightly cylindrical, the axes of the cylinders being perpendicu-
lar to the knife-edge. The idea of this as Professor Stokes afterwards explained it to me was that as a knife-edge probably rested on only a few points, a slight change of its position as to horizontality (of its aspect) would cause its weight to be differently distributed. I confess it seems to me that if a knife-edge is properly ground there will be a layer of air everywhere between it and the agate. But still it would be worth while to experiment with Foster’s plan.
The English pendulums all had two separate agates, ground into one plane (when they were plane). Becker’s balances also have two but the best balances in Germany I understand have only one.
Decidedly, I must invent some way of making experiments on the friction of knife-edges, as the subject is very obscure.
I had several important conferences with distinguished mathematicians and physicists in England in regard to the subjects of my work especially with Maxwell and Stokes.
I called upon the astronomer royal whom I wished to see not only on account of my having made pendulum experiments to determine the density of the earth but also because he had been rather polite to me when I was first in England. But this time he absolutely refused to see me without any explanation, although I wrote on my card who I was. I mentioned the circumstance several times in company in England and the only explanation offered was that his manners were known to be strange. I always added that it was possible he felt bitterly having been forced to go in to the observation of the ’70 eclipse by public opinion after my father’s action, and
that he was perhaps glad to show how little he shared the idea which governed the American’s conduct on that occasion, that scientific men of different nations should aid each other and cooperate. I must say however that Sir George Airy’s treatment of me was so remote from everything else which I experienced in England as to lead me to believe that it would occur but very seldom there as I am quite sure it would not happen at all anywhere else.
The computations were resumed as soon as Mr. Farquhar recovered from his attack, although I have not been able to do any actual numerical work and do not expect to do so. Fair progress was made for about a fortnight.
On the 27th I arrived in Hamburg and went at once to Repsold’s where he had my instrument all set up ready for my inspection. I occupied three days in the examination of all its parts and today I went and accepted it and paid for it. I enclose a photograph of it. There are a number of features of it, I confess, which my judgment cannot altogether approve. Swung in air, as it is, its proportions are not the best possible for eliminating the effect of resistance. But then I cannot admit that it will do to swing in air. Yet here in Germany & Switzerland they do not even read the barometer during the experiments.
Sawitsch was at one time in correspondence with the Messrs. Repsold on the subject of a vacuum chamber and they made drawings for one which I examined but did not approve of. The fact is they are all quite in the air about such things. But I want you to increase my money for the fiscal year 1875-76, if it seems to you proper to do so, so that I can make a first payment of $750 for a vacuum chamber for the reversible pendulum. I have not yet decided fully upon the plan of it but I have nearly so. It should be a circular cylinder of brass, which will be cheaper than copper, soldered together and with a hemispherical cup soldered on to the bottom. It shall have no windows. At the top a brass collar with great projecting wings to support it. The apparatus will all be put in, in one frame and fastened by screws at the top. On the collar will rest a truncated cone of glass
or by artificial light thrown down. The arc and transits of the pendulum are to be observed by a telescope pointing vertically down through the glass plate at the top by means of a totally reflecting prism at the bottom. The thermometer is to be a metallic one the whole length of the pendulum, mounted on a dummy pendulum the duplicate of the one swung. This metallic thermometer is to be read at the top by means of a very nice multiplying lever, of which I have an idea. The whole being underground is protected in the best way against changes of temperature and in a way which makes a field observatory nearly as good as a fixed one. I take some credit to myself for that device. I have imitated Basevi’s instrument in many points.
I will conclude this report by mentioning some matters of general scientific interest. It really seems as if Mr. Crookes had discovered a new force. You have doubtless heard of his experiments according to which radiant light falling on an absorbing surface produces pressure. Mr. Tyndall is warmly of the opinion that this is due to a longitudinal disturbance of the ether. He Tyndall says Stokes also thinks so.
Mr. Lockyer at the mint showed me some new spectroscopic experiments by which he seems to have made out that each metal has four successive espectra according to the intensity of the heat. He and Mr. Clifford think that on this basis they are going to distinguish between four different kinds of heat, produced by four different kinds of motion.
I also saw at the mint a spectroscopic method of quantitative assays which seemed very accurate.
The arctic expedition is to take a number of Wheatstone’s polariscopic clocks. He showed them to me and it was surprizing to see that they would give the time correct to two minutes. M. Cornu was in London while I was there shewing his apparatus for measuring the velocity of light by Fiseau’s method. I was glad to make his acquaintance as it may be useful to me in swinging in Paris. The new tough glass is wonderful. It is in a great state of strain which makes it optically useless and I fancy it cannot be ground without crumbling. Mr. Sylvester is developing a new and important branch of mathematics which has sprung from Peaucellier’s discovery of Parallel motion link-work.
Yours very respectfully
C. S. Peirce
Transcription by Transcription by Max Fisch (Peirce Edition Project), revised by Sara Barrena
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Proyecto de investigación "Charles S. Peirce en Europa (1875-76): comunidad científica y correspondencia" (MCI: FFI2011-24340)
Fecha del documento: 14 de agosto 2012
Última actualización: 14 de septiembre 2017