FIRST EDITION IN EXTREMELY SCARCE ORIGINAL WRAPPERS of two important papers on special relativity: Einstein’s discovery of the transverse Doppler effect as a test for special relativity and his response to Paul Ehrenfest on “the difficulty of applying Lorentz transformations to rigid bodies” (Pais).
“An interesting problem in relativity is the theory of the Doppler effect, the change in the frequency of light detected by an observer who is moving relative to the light source... A way to detect the relativistic Doppler effect was suggested by Einstein himself. He pointed out that when [the direction of the velocity of the source and position of the observer is] 90deg... the source is momentarily neither approaching nor receding from the observer. Just at that instant the observed light is emitted transversely to the direction of relative motion. According to classical theory, no change in frequency should be detected in this case. The relativistic formula, in contrast, predicts [a change]. This ‘transverse’ Doppler effect is due entirely to time dilation. Although the predicted shift is small, detection of any shift whatsoever would confirm the relativistic effect.
“The experiment is very difficult; the transverse Doppler effect is detectable only if [the angle] is almost precisely 90deg... For a long time, the necessary precision could not be achieved.
“The transverse Doppler effect was first demonstrated successfully in 1963 by Walter Kündig, who used a rotating turntable with an emitter of radiation at the center and an absorber on the rim. In such an arrangement, the relative motion of source and absorber is necessarily perpendicular to the path of the radiation... The results were consistent with Einstein’s formula within 1 percent” (Sartori, Understanding Relativity).
The Ehrenfest paper and Einstein’s response:
“As Einstein pointed out in his first paper on relativity, electrodynamic theory is based on ‘the kinematics of the rigid body, since the assertions of any such theory have to do with the relationships between rigid bodies (systems of coordinates), clocks, and electromagnetic processes... [With] regard to the contraction of lengths in the direction of motion, Einstein may be interpreted as follows: when one makes a measurement of length, one must either have the object in his frame of reference or, failing that, make simultaneous observations of the ends of the object... But since observers in different frames of reference will disagree about judgements of simultaneity, it follows that they will disagree as well with regard to judgements of length. The disagreement is not due to any dynamical change in the object; indeed, the construction and nature of the object are not even considered. Th disagreement is an artifact of the measuring process itself and may be traced ultimately to Einstein’s two postulates. Einstein maintained this kinematical view in his subsequent work. Thus when Paul Ehrenfest pleaded in 1907 that Einstein supply more information about his ‘theory of electrons’ so that a decision could be made on certain paradoxes of electron rigidity Ehrenfest had pointed out, Einstein’s reply was simply to deny that he had a theory of electrons. Rather, he said, his was a theory concerned with the relationship between rigid rods, perfect clocks, and light signals” (Galison et al., The Roots of Special Relativity).
Ehrenfest later became Einstein’s closest friend; this was the first of several formal objections to special relativity published by Ehrenfest as a young man. (The Ehrenfest paper precedes Einstein’s in this issue.) Weil 17, 18.
IN: Annalen der Physik, Band 23, No. 6, Heft 1, pp. 197-8; 206-8. Leipzig: Barth. 1907. Octavo, original wrappers. Blind stamp on front wrapper (Bates College - long ago deaccessioned). Tear to rear wrapper; split at spine (text block loose) and upper edge of front wrapper; some chipping along the edges. Text bright and very clean. Exceedingly rare in original wrappers.