PHYSICS: S. J. BARNETT 
51 
the poles and the other parts of the magnets. The (now) uniform field con- 
taining the condenser is conceived to be divided into. two parts as follows: 
an approximately fixed field beneath the plane of the upper surface of the 
lower plate, and above this plane a field whose tubes of induction move ap- 
proximately with the speed of the upper magnet. The induced electro- 
motive forces are thus restricted to the same regions as in the imaginary 
experiments of §4. 
6. In the experimental arrangement the lower condenser plate is (ordi- 
narily) connected by a wire with one quadrant pair of an electrometer. The 
other pair and the upper plate are connected (the latter through a key at will) 
to a thin metallic case forming a practically complete electric screen about the 
condenser-electrometer system. The wire joining the condenser and elec- 
trometer can be connected to the case by closing an electrically operated key 
K, thus short-circuiting both condenser and electrometer. A suitable cali- 
brating arrangement is provided. 
7. The calibration experiments give the deflection D which would be 
produced by charging the condenser to the potential difference E of §2 (the 
upper plate being disconnected from the case for the purpose), insulating the 
lower plate and electrometer by opening K, and reconnecting the upper plate 
to the case. 
8. The principal experiment, together with experiments for determining 
extraneous effects, gives the deflection d due to any charge on the lower plate 
produced when the upper magnet moves (with known speed) past the center 
of the fixed system, opening the key K at the center of the motion. An ex- 
tended series of experiments shows that d/D is zero within the limits of the 
experimental error. 
The investigation thus appears to support the hypothesis of §4, B, which 
assumes the existence of the aether, and to be inconsistent with the principle 
of relativity. 
I am indebted to Mrs. Barnett for a great deal of help in making the exper- 
iments, to Mr. Freund for mechanician's assistance, and to the Carnegie 
Institution and Professor Pegram for some of the instruments used. 
A detailed account of the work will be submitted for publication to the 
Phvsical Review. 
1 Barnett, S. J., Physic. Rev., Ithaca, N. Y., 35, 1912, (323-336) 
