Page:Collected Physical Papers.djvu/338

318 screen is next turned through 90°; the quadrants P and Q are now exposed to light, and R and S shaded

from it. The resulting upset of the balance and the galvanometer deflection is now in an opposite direction.

The reliability and the sensitiveness of the Quadrant Method may thus be tested by obtaining equal and opposite responses under alternate illumination of the two pairs of quadrants; the test in confirmation of the above will be found in records given in figure 93.