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Excerpted from The Journal of the Academy of Science of St. Louis
Vol. 23, 1916 and 1917
[Reprinted in "Homemade Lightning" by R.A. Ford, Tab Books]
[see The Electrical Experimenter, March 1918, for a related article.]
This experiment -- performed by Dr. Francis Naphir, professor of physics at Washington University, St. Louis, Missouri -- is a modification of the Cavendish experiment of 1798. In this earlier experiment, Henry Cavendish used a delicate torsion balance to determine the density of the earth.
The first phase of Dr. Nipher's experiment, performed in 1916 and 1917, is shown in figures 1 and 2. The room had a concrete floor and granite walls, and the equipment was mounted on a massive bench. Thermometers nearby indicated that parts of the apparatus did not vary in temperature from each other by more than 1.5 degrees C. The 1-inch lead ball was suspended with an untwisted silk thread approximately 180 cm. long, and centered inside a 5-inch square iron box or Faraday Shield. A horizontal slit in the box's side, covered with a glass plate, permitted Dr. Nipher to observe scale deflections with a telescope.
Next to this iron box, he placed an insulated 10-inch-diameter lead sphere, with a copper wire keeping this sphere and the metal box at the same potential. To eliminate errors caused by temperature differences, Naphir used a cardboard shield and kept the observer's body below and away from the apparatus.
Figure 1 shows the normal attraction between the uncharged masses. In figure 2 an influence generator, located in the next room, is joined to the large mass. After about twenty minutes, the 1-inch lead ball slowly moved to the opposite side with a deflection about twice the normal gravitational attraction regardless of the polarity used.
In the last phase of this experiment in 1917, a torsion balance with two large spheres and two small balls gave the same result. Next, the large lead spheres and two small balls were replaced with charged metal boxes conatining cotton batting. This gave no deflection, eliminating electrostatic force as the cause. Finally, the influence generator was replaced with a low-voltage ac current passing through the two large lead spheres. This also produced a repulsion, but one of smaller value.
