Page:Collected Physical Papers.djvu/338

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

Fig. 92. The Quadrant Method of response by variation of electric resistance. Two opposite quadrants of the leaf are shaded. Electric connections are made at the junctions of the quadrants and not at the middle as shown in figure.

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.