CONFERENCE ON MICHELSON-MORLEY EXPERIMENT 385
It is interesting that in the ideal case
= X ô-ô'= X hß2 cos 2Ô__ \h
27r Aa 27T ß2 COS 2# 27T *
That is, we have a constant position, independent of the orientation of the instrument. If Michelson had devised the experiment so as to have no fringes, but light in a certain position of the ideally adjusted interferometer, expecting to have darkness in another position, because of the phase difference, the experiment would not have proved anything.
Dr. Kennedy’s arrangement occupies an intermediate position. He takes fringes of considerably greater width. The width necessary to produce an appreciable error is about 250 cm, however, and it is quite certain that his fringes were not as wide as that. Professor Hedrick’s theory is, however, very interesting and important in connection with Kennedy’s experiment.
VI. PROFESSOR PAUL S. EPSTEIN (CALIFORNIA INSTITUTE
I cannot report to you today on anything of my own. What I intended was a short review of some recent experiments which relate to Mr. Miller’s experiment, and which have been performed mainly outside of Pasadena.
I shall give you a brief account of three experiments, carried out by Tomaschek in Germany, by Chase in Pasadena, and by Piccard in Brussels.
In one of his experiments Tomaschek used the following arrangement. In the immediate neighborhood of a charged condenser I (Fig. 17) was suspended a magnetic needle II. The experiment was intended to check an old idea of Röntgen’s which was as follows: The charged condenser, being in motion, represents a system of two parallel currents moving in opposite directions. These currents produce a magnetic field which should exert a force on the magnetic needle. In case the condenser is in motion relative to the ether, a deflection of the magnetic needle should be found. In reality this device cannot provide a crucial test for a decision between the old and the new theory. An exact analysis shows that both theories lead
PAUL S. EPSTEIN
to the same result because the effect is of the first order. The explanation why no effect exists lies in the fact that it is not the condenser alone which moves, but also the indicating needle. This gives
Moreover, Tomaschek tried the experiment with a metal cover around his needle. By this arrangement, cutting out all the magnetic actions between I and //, he eliminated any effect which might have existed without shielding. So it is not surprising that he did not obtain a positive effect. He might indeed have saved his efforts by not trying the experiment at all.
Tomaschek, and independently Mr. Chase in our laboratory, repeated the old experiment of Trouton and Noble, as they think, in a much more precise way. The underlying idea is the following:
Suppose I (Fig. 17) to be a charged condenser, suspended in such a way that it can rotate. For a condenser at rest there exists only a force of attraction between the two plates due to the charges of opposite sign. Now the apparatus being in motion with the velocity v (Fig. 18) means that the positive charge is moving in a magnetic field originated by the moving negative charge, and vice versa. Hence two additional forces are exerted on the condenser which would manifest themselves as a torque, so that a rotation of the condenser should be expected. It is easy to calculate this torque, M, which is
where Z7 equals the energy content of condenser, e the dielectric constant of material filling the condenser, and v the azimuth
rise to a second torsional moment which just balances the first one.
characterizing the projection of v on the plane of the condenser in relation to the suspension.