214 Dr. R. A. Houstoun on 



in the respective positions to that which would enter it if 

 the plate were in the immediate proximity of the opening, 

 i. c. if r l9 r 2 , and r^ are the distances in the respective cases, 



Kt r°° 2 K 9 r 2 



I calculate — I X ^-, and — i x ^p-. For the two expressions 



we obtain the values 0*0827 and 0*00602 respectively. The 

 difference between the two expressions is 0'077. If I 

 assume that about equal scattered radiation is propagated 

 backwards, this difference, which comes out as a difference 

 in the apparent absorption, will amount to ca. 3*9 per cent, 

 of the absorption caused by scattering. According to the 



figures given above it only amounts to a.acm .n.-Mo °^ 



the total absorption. The difference will then be 1*5 per cent, 

 of the total absorption. This is in fair agreement with the 

 Auren experiments. 



In addition to the above calculation I wish to mention 

 that, for small values of z, K is more readily denoted by 

 developing in the formula (4), the integrand of a power 

 series and integrating term by term. So the following 

 expression is arrived at : 



Nobel Institution of Physical Chemistry, 

 Stockholm, June 1918. 



XIX. Fizeaus Experiment and the JEther. By Dr. R. A. 

 Houstoun, Lecturer on Physical Optics in the Lniversity 

 oj Glasgow*. 



§ 1. TN a celebrated experiment performed in 1859 Fizeau 

 X showed that the velocity of light in a tube con- 

 taining running water could be explained on the assumption 

 that the aether in the tube was dragged with the water with 

 a velocity v(l — 1//-& 2 ), where v is the velocity of the water. 

 The experiment was repeated with greater accuracy by 

 Michelson and Morley in 1886, and Fizeau's result verified. 

 According to the theory of H. A. Lorentz published in 1895, 

 however, the velocity of the aether-drift in the tube is 

 given by 



&* +1 . 



\ fi 2 fi d\/ 



* Communicated by the Author. 



