London: Taylor & Francis, 1904.
First edition, rare offprint issue, of the Brace experiment which attempted to detect the FitzGerald-Lorentz contraction of bodies in their direction of motion through the aether. “De Witt Bristol Brace (1859-1905), professor of physics and specialist in optics at the University of Nebraska, is best remembered for his experimental test of the Lorentz-Fitzgerald contraction hypothesis ... In 1904 the opportunity arose for Brace to apply the extremely sensitive optical techniques he had developed to one of the crucial problems of his day. Two years earlier, Lord Rayleigh had proposed that the Lorentz-Fitzgerald contraction, if it existed, might produce an observable double refraction in a moving transparent medium. [Double refraction, also called birefringence, an optical property in which a single ray of unpolarized light entering an anisotropic medium is split into two rays, each traveling in a different direction.] Rayleigh made experiments in which he failed to find the predicted effect, but his work was not quite accurate enough to be conclusive. Brace pointed this out and reconducted the investigation in his own laboratory, establishing beyond a doubt the absence of double refraction caused by movement of the refracting medium through the ether. This did not disprove the contraction hypothesis, but Brace at first believed that it did. Joseph Larmor showed that double refraction need not result from Lorentz contraction if matter is composed of electrically charged particles that contract in the same proportion as large bodies; he thus saved the Lorentz hypothesis and gave the electron its status as a fundamental particle of matter” (DSB). No copies listed on ABPC/RBH.Nineteenth century physicists had assumed that light waves propagate through a medium, which was called the aether, in the same way that sound waves require a medium such as the air to transmit them. They argued that light should have a different velocity when traveling on the same direction as the Earth’s motion around the Sun as it would when traveling in the opposite direction. This effect, assuming it existed, was called ether-drift. However, towards the end of the century experiments had failed to detect the ether-drift, most famously in the Michelson-Morley experiment of 1887. In his great work Versuch einer Theorie der electrischen und optischen Erscheinungen in bewegten Körpern (1895), Hendrik Antoon Lorentz attempted to explain the negative result of the Michelson-Morley experiment by proposing that moving bodies contract in their direction of motion by a factor √1 – v2/c2, where v is the speed of the body relative to the aether and c is the speed of light (a hypothesis also made, unknown to Lorentz, by the Irish physicist George Francis FitzGerald). “Lord Rayleigh interpreted this contraction as a mechanical compression which should lead to optical anisotropy of materials, so the different refraction indices would cause birefringence. To measure this effect, he installed a tube of 76 cm length upon a rotatable table. The tube was closed by glass at its ends, and was filled with carbon bisulphide or water, and the liquid was between two nicol prisms. Through the liquid, light (produced by an electric lamp and more importantly by limelight) was sent to and fro. The experiment was sufficiently precise to measure retardations of 1/6000 of a half wavelength, i.e., of the order 1.2 ×10−10. Depending on the direction relative to Earth’s motion, the expected retardation due to birefringence was of order 10−8, which was well within the accuracy of the experiment. Therefore, it was, besides the Michelson-Morley experiment and the Trouton–Noble experiment, one of the few experiments by which magnitudes of second order in v/c could be detected. However, the result was completely negative. Rayleigh repeated the experiments with layers of glass plates (although with a diminished precision by a factor of 100), and again obtained a negative result [‘Does Motion through the Aether cause Double Refraction?’, Philosophical Magazine 4 (1902), pp. 678–683].“However, those experiments were criticized by DeWitt Bristol Brace (1904). He argued that Rayleigh hadn't properly considered the consequences of contraction (0.5 × 10−8 instead of 10−8) as well as of the refraction index, so that the results were in no way conclusive. Therefore, Brace conducted experiments of much higher precision. He employed an apparatus that was 4.13 m long, 15 cm wide, and 27 cm deep, which was filled with water, and which could be rotated (depending on the experiment) about a vertical or a horizontal axis. Sunlight was directed into the water through a system of lenses, mirrors and reflexion prisms, and was reflected 7 times so that it traversed 28.5 m. In this way, a retardation of order 7.8 × 10−13 was observable. However, also Brace obtained a negative result. Another experimental installation with glass instead of water (precision: 4.5 × 10−11), also yielded no sign of birefringence.“The absence of birefringence was initially interpreted by Brace as a refutation of length contraction. However, it was shown by Lorentz [‘Electromagnetic phenomena in a system moving with any velocity smaller than that of light’, Proceedings of the Royal Netherlands Academy of Arts and Sciences 6 (1904), pp. 809–831] and Joseph Larmor [‘On the ascertained Absence of Effects of Motion through the Aether, in relation to the Constitution of Matter, and on the FitzGerald-Lorentz Hypothesis,’ Philosophical Magazine 7 (1904), pp. 621–625] that when the contraction hypothesis is maintained and the complete Lorentz transformation is employed (i.e. including the time transformation), then the negative outcome can be explained. Furthermore, if the relativity principle is considered as valid from the outset, as in Albert Einstein's theory of special relativity (1905), then the result is quite clear, since an observer in uniform translational motion can consider himself as at rest, and consequently won't experience any effect of his own motion. Length contraction is thus not measurable by a comoving observer, and has to be supplemented by time dilation for non-comoving observers” (Wikipedia).Brace “received his bachelor’s degree from Boston University in 1881 and went on to graduate study at MIT and Johns Hopkins University. In 1883 his admiration for Kirchhoff and Helmholtz took him to Berlin, where he wrote a doctoral dissertation on magneto-optical effects. In 1888, shortly after his return to the US, Brace became professor of physics at the University of Nebraska, where he remained until his death” (DSB).
8vo, pp. 317–329. Original pink wrappers. A fine copy.