Physics. — “The Propagation of Light in Moving Transparent 
Solid Substances. 1. Apparatus for the Observation of the 
Fizrav-Bffect in Solid Substances.” By Prof. P. Zeeman. 
(Communicated in the meeting of May 3, 1919). 
1. As a result of an experiment by Araco with a glass 
prism FrrsneL drew up his bold hypothesis on the convection co- 
efficient in 1818. When in 1851 Fizeav wanted to put Frrsner’s 
hypothesis to the test, he experimented, however, with water, and 
examined whether or not the velocity of light in standing water 
differs from that in moving water. 
There are many reasons to be adduced for carrying out an ex- 
periment, so exceedingly difficult as that of Fiznau, in the first place 
with water; it is, however, also interesting to examine the motion 
of light in sold, transparent, rapidly moving substances. In this 
connection experiments with rapidly moving quartz and glass have 
been made by Miss Sneruiace and myself. In this communication 
I will give the description of the apparatus with which these expe- 
riments have been made. It may be well to call attention to a few 
points referring to Fiznau’s experiment with water. 
Let c be the velocity of light in vacuo, u the index of refraction 
of the water, w the velocity of the water with respect to the tube 
in which it moves; then the velocity of propagation of the light 
with respect to the tube is according to Frusne.: 
Pi] 1 
Telt) OEREN oy oro (1) 
lu u 
In this the upper or the lower sign is to be taken according as 
the water and the light move in the same or in opposed directions. 
In 1895 Lorentz demonstrated that FreESNeEr’s convection coefficient 
in a dispersive medium must be replaced by: 
; i À du 
EE aa 
This changes formula (1) into: 
ieee Wr 
e(t) at CAREER) 
u mees ah dA 
The experiments made by Frizrav in 1851, plead in favour of 
