Method of increasing ShocTcs, &cc. 141 



It may also be worth mention, that by using the needles as before, 

 I obtained with this apparatus, shocks from a single pair of plates of 

 only four square inches, (single surface.) We have then in this in- 

 strument a battery by itself, from which shocks of all grades can be 

 obtained, and in cases of the medical application of galvanism, it 

 must prove far more convenient than the ordinary methods. 



POSTSCRIPT. Salem, June 8, 1836. 



One of the most pleasing experiments with the coil, is breaking 

 the circuit with a revolving spur wheel. In former experiments, I 

 produced the revolution of the wheel with a string, as in the wheel 

 tinder box, having failed to effect it with a magnet. But I have 

 since invigorated my calorimotor, by removing and cleansing the 

 zinc plates, and a small horse shoe magnet is now sufficient to pro- 

 duce rapid revolutions, with the most brilliant results. The circuit 

 in this case is terminated in cup 2, as the rotations diminish in pro- 

 portion to the length of the coil used. The wheel is fitted with a 

 wooden stand and trough, precisely as for magnetic rotation. The 

 deflagration of the mercury is extremely vivid, giving copious fumes. 

 If the experiment is performed in a dark room, it exhibits in a superb 

 manner, the well known optical illusion, of a wheel in rapid motion 

 appearing to be at rest. As the wheel is illuminated by a rapid se- 

 ries of sparks, it does not appear to be exactly at rest, but exhibits a 

 quick vibratory movement. I have before alluded to the nature of 

 the shocks given by the wheel, but with this self regulating appara- 

 tus, an assistant can be dispensed with, and shocks of any duration 

 and degree, can be obtained, by immersing the copper handles as 

 before directed. The strongest shock being obtained by immersing 

 the copper handles in cups 6, and the negative cup on the battery. 

 This last experiment is difficult to explain. The left hand being in 

 cup 6, it is immaterial whether the right hand is carried to the posi- 

 tive or negative cup on the battery; a strong shock is felt in both ca- 

 - ses, but that from the negative cup is somewhat stronger, and is the 

 real maximum, if the circuit terminates with half the coil. 



