5$ THE SIGNS OF LIFE [LECT. 



31. Cause < Effect. I have thought it hardly necessary to 

 repeat to you a series of experiments similar to the preceding, 

 but with condenser discharges in place of break induction 

 shocks. Moreover, time forbids that I should do so, with the 

 explanation necessary to bring out the particular advantages 

 of this method. We may find time for this at a future 

 lecture, meanwhile I will again refer you to the paper already 

 quoted,* where you will find experimental justification for the 

 statement that the electrical energy of excitation is greatly 

 exceeded by the electrical energy of the blaze-current that it 

 arouses. 



32. Galvanisation. Experiment V. The fifth and last 

 experiment on our list is to show how the direction of a 

 blaze - current aroused by an induction shock, can be modi- 

 fied by the passage of a galvanic current through the eye- 

 ball. 



An eyeball is put up as before, the compensator is arranged 

 to give a current of comparatively high E.M.F. (o.i volt) through 

 the eyeball and galvanometer. I first take this galvanic current 

 in the positive direction, when, of course, the galvanometer spot 

 is driven off scale to your right. I bring the spot back in scale 

 by means of a controlling magnet, and as soon as it is steady, 

 send a break induction shock through the circuit (comprising 

 the eyeball, compensator, and galvanometer in series) first in the 

 positive, then in the negative direction. In both cases the 

 positive deflections are greatly augmented. 



Then I reverse the galvanic current to the negative direction, 

 readjust the spot on scale by means of the controlling magnet, 

 and repeat the test. Both the induction shocks, positive and 

 negative alike, now give negative deflections, i.e., blaze-currents 

 in the same direction as the galvanic current. Nothing of the 

 sort happens, I should add, in the case of a dead or " electrocuted " 

 eyeball. If I had made the experiments upon an eyeball giving 

 negative blaze-currents of the third type described above, you 

 would have witnessed an augmentation of these currents during 



* Phil. Trans. Roy. Soc., vol. 194 B., p. 183. 1901. 



