Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 tij - CAUSE : EFFECT Let us consider the three cases :— y y y S7 Fig. 17.—Straight. The effect Y varies as its cause X. Equal increments of cause produce equal increments of effect. The cause/effect cuiTe is a straight line. Concave. The effect T varies more rapidly than its cause X. Equal increments of cause produce increasing incre- ment of effect. The cause / effect curve is convex to its abscissa OX. Convex. The effect Y varies less rapidly than its cause X. Equal
Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 tij - CAUSE : EFFECT Let us consider the three cases :— y y y S7 Fig. 17.—Straight. The effect Y varies as its cause X. Equal increments of cause produce equal increments of effect. The cause/effect cuiTe is a straight line. Concave. The effect T varies more rapidly than its cause X. Equal increments of cause produce increasing incre- ment of effect. The cause / effect curve is convex to its abscissa OX. Convex. The effect Y varies less rapidly than its cause X. Equal increments of cause produce diminishing increments of effect. The cause / effect curve is concave to its abscissa OX. And now turn to the case in point, where the cause X is the intensity of a light, and the effect Y the magnitude of a galvano- metric deflection (which we shall assume to measure magnitude of electrical change, and therefore magnitude of retinal change). With a light of suitable strength, varied on an arithmetic scale constructed in conformity with the law that luminosity varies inversely as the distance squared, we find the following series of results from the given series of stimuli:— Stimulation by light . 2 4 6 8 10 X Retinal change . . 208 248 274 296 326 Y which, plotted as described above, gives the curve figured below as that of the retinal effects of medium illumination. , ) 5 ! 1 2 \ ) J \ J Units qP ... , eccciCabion. Weak. Medium. -! !' Strong. 20 40 60 ao 100 Fig. 18.—Frog. Retinal response to illumination of constant duration and of varying strength. The unit of light is a standard candle at a distance of lo feet from the eyeball. Now this curve, concave to its abscissa OX, with the effect Y increasing less rapidly than its excitant cause X, is in
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