were projected onto a pair of photoresistors that consisted of two arms of a Wheatstone bridge. Such a set-up is capable of measuring fringe shifts with a sensitivity up to 10~5 fringe (14). The whole system rested on a heavy turntable (about 3.5t), which floated on mercury.
The output of the fringe-sensing system was connected to the ?/-input of an xy recorder, the x input being a voltage proportional to the sine of the angle of rotation of the table.
A positive result would have appear ed on the xy recorder as shown in
Fig. 3. The Figure represents the trace going from East, North, West, South and back again to East, the total fringe shift being A. The effect is a second-order one (there should be no difference between East and West, nor between North and South), thus the line EW should be horizontal and the lines ENW and WSE should coincide.
Fig. 3. - Idealized recorder trace.
4. - Measurements, results and conclusions.
In our measurements, the line E\Y was not exactly horizontal, indicating a drift during the measurement. This shift was isolated as thermal. It was small and not bothersome since we measured directly with respect to the line E W. The more bothersome difficulty was the first-order effect of the lines ENW and WSE not exactly coinciding (S and N lay on different sides of the EW line). After much investigation this effect could only be attributed to strains induced in the table by the earthТs magnetic field. The effect decreased when a magnetic shield was used.
The magnetic field effect was the limiting factor in the accuracy attainable by the system. The fringe-sensing system operated at a sensitivity of 3000 mm/fringe. The final experimental result was a A (see Fig. 3) measured to be less than one mm.
Thus,
(19)
From this we can place an upper limit to the velocity of the earth through the ether. Using eq. (18), we obtain
(20)
C14) J. Shamir, K. Fox and S. G. Lipson: Appl. Opt.. 8. 103 (1969).
Substituting the values of A, A, I and n in this experiment
we obtain (21) or (22)
The upper limit to the velocity of the earth through the ether (6.64 km/s) that was obtained in this experiment is much less than the orbital velocity of the earth around the sun (about 30 km/s). The experimental basis of special relativity is thus enhanced by this negative result.
* * *
We wish to thank N. Rosen for several helpful comments, and M. Albahari for fruitful discussions which helped to initiate the present experiment.
RIASSUNTO O
Sebbene la teoria della relativity ristretta sia quasi generalmente accettata come una teoria verificata, gli esperimenti esistenti non possono distinguerla da un certo numero di altre teorie rivali che suppongono lТesistenza di un sistema di riferimento privilegiato (etere), e le contrazioni fisiche di Lorentz. Si dimostra che lТesperimento di Michelson e Morley, realizzato in un mezzo solido trasparente, rende possibile una tale distin-zione. II risultato negativo di questo esperimento migliora la base sperimentale della relativity ristretta.
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