XIV. 
THE RESULTS OF AN ELECTRICAL EXPERIMENT, INVOLVING THE 
RELATIVE MOTION OF THE EARTH AND ETHER, SUGGESTED BY 
THE LATE PROFESSOR FITZGERALD. By FRED. T. TROUTON, D.Sc., 
F.R.S., University Lecturer in Experimental Physics, Trinity College, Dublin. 
(Read November 20, 1901.) 
].—Proressor Firz GerRAup’s ARRANGEMENT. 
In the autumn of 1900 Professor G. F. Fitz Gerald proposed an electrical experi- 
ment, with the object in view of detecting any relative velocity there might be 
between the Earth and ether. 
The method has not up till now been published, except at a meeting of the 
Dublin University Experimental Science Association last May. 
Professor Fitz Gerald asked me to carry out the proposed experiments. These 
I began at once, but owing to delays in preparing the apparatus and getting it 
into working order, only some preliminary determinations were made before his 
ulness and death. 
The fundamental idea of the experiment is that a charged electrical condenser, 
when moving through the ether, with its plates edgeways to the direction of 
motion, possesses a magnetic field between the plates in consequence of its motion, 
in accordance with the generally held view that a moving charge is equivalent to 
an electric current. 
The question then naturally arises as to the source supplying the energy 
required to produce this magnetic field. If we attribute it to the electric gene- 
rator, say a battery,* there is no difficulty indeed, as to there being energy 
enough to do it, for, in general, the energy supplied by a battery when charging 
a condenser is double that stored in electrostatic strains in the condenser— 
LQ =iLHQ + energy lost as heat, ete. 
Fitz Gerald’s view, however, was that it would be found to be supplied through 
there being a mechanical drag on the condenser itself at the moment of charging, 
very similar to that which would occur were the mass of any body situated on the 
surface of the Earth to suddenly become greater. Again in discharging, the 
condenser should experience an impulse of like amount, but now in the opposite 
or forward direction. To estimate the extent of this blow, suppose a condenser 
of capacity P to be moving edgeways through the ether with the velocity uw, and 
* See Part II. of this Paper. 
TRANS. ROY. DUB. SOC., N.S., VOL. VII., PART XIY. 2H 
