al 
LAXII. Relative Motion of Earth and Aither. 
By A. A. MicHEtson *. 
- the Physikalische Zeitschrift + a method is proposed by 
W. Wien for deciding the important question of the 
trainement of the ether by the earth in its motion through 
space, by measuring the velocity of light in one direction— 
that is, without reflecting it back trom the distant station. 
The essentials in the proposed method are two Foucault 
mirrors, or two Fizeau wheels (one at each station ) revolving 
at the same speed. ‘The control for this synchronism is to be 
furnished by the ‘“ Konstanz des hindurchgehendes Lichtes 
oder in bekannten stroboskopischen Methoden.” 
The flaw in the proposed method—as was pointed out by 
Simon Newcomb as long ago as 1880—lies in the fact that the 
effect. which it is proposed to measure is exactly the same as 
the effect on the light which is to furnish the test of 
synchronism. 
In November 1887 I proposed a method differing in no 
essential respect from the foregoing, except that the ‘control 
of synchronism was to be furnished by electrical methods. 
This was before the celebrated work of Hertz showed that 
electrical impulses differed in no essential from light. This 
identity constitutes the same objection to this plan f. 
The possibility of «a mechanical method of control was 
pointed out in a paper on the ‘* Velocity of Light,” in the 
Philosophical Magazine, March 1902. This is based on 
some experiments made jn 1899, which showed that the 
vibrations of a tuning-fork could be transmitted over a mile 
of piano-wire with but little diminution of amplitude §. 
Part Ii, 
Suppose it were possible to transmit two pencils of light 
in opposite directions around the earth parallel to the 
equator, returning the pencils to the starting-point. If the 
rotation of the earth does not entrain the ether, it is clear 
that one of the two pencils will be accelerated and the other 
retarded (relatively to the observing apparatus) by a quantity 
proportional to the velocity of the earth’s surface, and to the 
length of the parallel of latitude at the place; so that a 
* Communicated by the Author. 
+ 5 Jahrgang, No. 19, Seite 585-586. 
t Possibly a spirally wound wire—which transmits electrical oscil- 
lations with a velocity less than that of light—would be differently 
affected, and thus furnish a solution of the problem. 
§ Perhaps, however, even mechanical impulses would be affected by 
the earth’s motion in such a way as to neutralize the expected effect. 
