Motion of the Earth and Ether, suggested by the late Professor Pitz Gerald. 383 
relative motion of the Earth and the ether by means of the interference 
of light. 
The explanation of this, which he had himself, simultaneously with Lorentz, 
suggested, was that matter altered in linear dimensions according to the direction 
of motion through the ether, and to an extent to just neutralize the calculated 
optical effect. From some such cause a diminution of the electrostatic energy 
might be brought about when the condenser was in the edge-wise position, just 
sufficient in amount to provide the energy required for the magnetic field. 
TIl.—On tHe PossIpILiry OF OBTAINING A TURNING ForCcE FROM THE MOoTION OF 
THE EARTH THROUGH SPACE. 
If we suppose the energy for the magnetic field between the plates of 
a charged condenser when moving ‘‘ edgewise ” through the ether to be 
supplied from the same source as that which charges the condenser, we are led to 
the curious conclusion, that a charged condenser tends to set itself flatways 
to the direction of motion though the ether. This may be easily understood from 
the following considerations. 
A condenser charged when moving ‘‘edgewise” has more energy to be 
supplied it than when moving ‘ flatwise.’” Now suppose a condenser which 
is placed with its plates ‘‘ flatwise” to the motion through the ether, to be first 
charged and insulated, then turned round till it is standing with its plates 
‘Cedgewise” to the motion through the ether. The extra energy belonging 
to the magnetic field, which we suppose to now exist, must come from work done 
in turning it round through the 90°. That is to say, the condenser resists with, or 
exerts, a couple in the opposite direction to the turning motion. 
Thus we see, on the assumption made above, that charged condensers must 
tend to set themselves at right angles to the direction of motion through 
the ether. When placed exactly ‘ edgeways” to the motion, there is unstable 
equilibrium; but when inclined to either side, rotation to the position at right 
angles tends to take place indiscriminately as to the sign of the charges on the 
plates. This follows at once from the energy of the magnetic field depending on 
the squares of the directed quantities in question. The value of the torque 
increases with the angle of inclination, till it reaches its maximum half way 
between the two positions of ‘‘ edgeways” and right angles to the motion through 
the ether, at each of which it is zero. For if ¢ is the angle of inclination of the 
plates of the condenser to the direction of motion through the ether, the 
velocity of flow parallel to the plates is wcos¢. Thus the energy of the 
magnetic field is in this case 7’= 34K PLw cos’, and the couple at any angle 
> 
: WP : 
gh is — a or 3pKPEHw sin 2¢, this obviously has zero value for values 0° and 
90°, and a maximum value for ¢ = 45°. 
TRANS. ROY. DUB. SOC., N.S., VOL. VI., PART XIV. 21 
