176 DOVE ON THE ELECTRICITY OF INDUCTION. 



the remarkable phaenomenon was observed with the connexions 

 I and II and II and III, in both of which cases the final extra 

 current was active, that the shocks, which were perceptible on 

 the insertion of iron into the extra spiral consisting of the two 

 commonly used spirals, disappeared when the keeper was rapidly 

 rotated, and with a still more rapid rotation a physiological ac- 

 tion again appeared. This may possibly be explained upon the 

 supposition, that when the rotation is slow the current excited 

 in the extra spiral by the action of the coils of wire upon each 

 other is formed simultaneously with the current induced in these 

 wire coils by the evanescent magnetism of the inserted iron, so 

 that then the maxima of intensity of both currents coincide. 

 With a more rapid revolution, on the contrary, this latter cur- 

 rent remains behind the former, so that with a certain velocity 

 of rotation its maxima coincided with the minima of the former. 

 In this case a current of unchanged intensity would traverse the 

 body, which giving rise to a perfectly uniform sensation would 

 not be perceived ; similar phaenomena have been observed in re- 

 lation to tliis with preparations of the frog. With a yet more 

 rapid rotation the maxima again coincide, and produce inequali- 

 ties of intensity which make themselves perceptible. Thus it 

 would also be explained why these physiological phaenomena of 

 interference can only occur to the full extent, namely, to the 

 point of complete evanescence, with a determinate mass of iron, 

 and why we are able to obtain them with the greatest ease by 

 using iron wires, the number of which can be regulated accord- 

 ingly*. 



2. Sparks. 



80. As the extra spiral and the keeper are included in the cir- 

 cuit of the current when complete metallic connexion is made, we 

 obtain immediately at the cylinder w^ the same case as was de- 

 termined in the physiological experiments by the connexion of I 

 and II, namely, />— A + E. But as, during the rotation of the 

 keeper from 0° to 90°, the iron enclosed in the extra spiral be- 

 comes magnetized, which magnetism cannot become quite evanes- 



* In all determinations of the increase or decrease of a physiological action 

 mentioned in this memoir, I have never trusted to my own judgement alone, 

 but have always called in the assistance of others. In the course of the experi- 

 mental series, which were often very extensive, and required generally two ob- 

 servers, I have had to thank for their assistance the Messrs. Von Wys, Kopp, 

 Du I^ois and Karsten. 



