90 WRITINGS OF JOSEPH HENRY. [1835 



is drawn across the edges of the zinc plates, the other end 

 being in contact with the copper pole. 



Another method of producing the shocks is to place the 

 spiral between two batteries, each of a single pair, so as to 

 connect the copper of one with the zinc of the other. If the 

 extreme poles of this compound arrangement be terminated 

 by the copper handles, and these be brought in contact, 

 holding one in each hand, a deflagration of the metal will 

 be produced, and a thrilling sensation, scarcely supportable, 

 felt in each arm. The effect is much increased if the 

 handles are rough. Two cylinders of cast zinc terminating 

 the poles were found to produce the greatest effect when 

 rubbed on each other. 



To exhibit these phenomena in a striking manner a gal- 

 vanic battery of considerable size is required. I have used 

 one for the purpose containing about forty feet of zinc sur- 

 face, estimating both sides of the plate. This battery was 

 first immersed for a short time in a strong solution of acid, 

 to dissolve the coating of oxide, and then removed to a ves- 

 sel containing pure water. The small quantity of acid ad- 

 hering to the plates was sufficient to produce, by means of 

 the spiral, the deflagration of the metals, which would shock 

 and snap for many hours in succession, while with a short 

 conductor the battery in the same state gave no signs of 

 electricity. 



This will be found an economical method of exhibiting 

 some very interesting experiments with the calorimotor. 

 After having shown the ordinary heating powers of the in- 

 strument with strong acid, transfer the plates to a trough 

 containing pure water, and the action of the coil may be 

 shown for an almost indefinite time, at little or no expense 

 of zinc or acid. 



The spiral produces no increased effect when applied to a 

 galvanic trough of one hundred four-inch plates. If how- 

 ever a coil of five or six hundred feet of wire be substituted, 

 an increase of action will be manifest. The length of the 

 coil must be in some ratio to the "projectile" force of the elec- 

 tricity, and also the quantity to the thickness of the con- 

 ductor, in order to produce a maximum result. Thus, when 



