416 The Theory of Aether and Electrons in the 



stars in the line of sight, which has proved of great service in 

 astrophysical research, was suggested by Fizeau in 1848.* 



Passing now from the astronomical observatory, we must 

 examine the information which has been gained in the physical 

 laboratory regarding the effect of the earth's motion on optical 

 phenomena. We have alreadyf referred to the investigations 

 by which the truth of Fresnel's formula was tested. An 

 experiment of a different type was suggested in 1852 by 

 FizeauJ who remarked that, unless the aether is carried along 

 by the earth, the radiation emitted by a terrestrial source should 

 have different intensities in different directions. It was, how- 

 ever, shown long afterwards by Lorentz that such an experiment 

 would not be expected on theoretical grounds to yield a positive 

 result ; the amount of radiant energy imparted to an absorbing 

 body is independent of the earth's motion. A few years later 

 Fizeau investigatedll another possible effect. If a beam of 

 polarized light is sent obliquely through a glass plate, the 

 azimuth of polarization is altered to an extent which depends, 

 amongst other things, on the refractive index of the glass. 

 Fizeau performed this experiment with sunlight, the light 

 being sent through the glass in the direction of the terrestrial 

 motion, and in the opposite direction ; the readings seemed to 

 differ in the two cases, but on account of experimental difficulties 

 the result was indecisive. 



Some years later, the effect of the earth's motion on the 

 rotation of the plane of polarization of light propagated along 

 the axis of a quartz crystal was investigated by Mascart.^f The 

 result was negative, Mascart stating that the rotation could 

 not have been altered by more than the (l/40,000)th part when 

 the orientation of the apparatus was reversed from that of 



* An apparatus for demonstrating the Doppler-Fizeau effect in the laboratory 

 was constructed by Belopolsky, Astrophys. Journal xiii (1901), p. 15. 



t Of. pp. 117-120. + Ann. d. Phys. xcii (1854), p. 652. 



\ Proc. Amsterdam Acad. (English edition), iv (1902) p. 678. 



|| Annales de Chim. (3) Ixviii (1860), p. 129; Ann. d. Phys. cxiv (1861), 

 p. 554. 



H Annales de 1'Ec. Norm. (2) i (1872), p. 157. 



