546 DR. DAVY ON THE TORPEDO. 



appeared to be completely interrupted. In very many experiments, employing the 

 most active fish, if there were any visible space between the ends of the red-hot pla- 

 tina wire, I never witnessed the galvanometer in connexion with one wire affected, 

 nor could obtain a shock. Reasoning on the subject, this perhaps is what might be 

 expected, considering that the surface of the fish is a better conductor than air. One 

 fact, however, which I had observed, afforded some encouragement to persist in the 

 trials, the fact that the torpedinal electricity passes through distilled water, wliich is 

 a worse conductor of it than its own skin. 



I thought it possible that by insulating the Torpedo on a plate of dry glass, and 

 wiping its circumference dry and smearing it with oil, that either a spark might be 

 procured, or that the galvanometer might be affected. But in this, too, I have been 

 disappointed ; not even in flame, when the interruption of the circle has been only 

 just visible, has any effect on the instrument been produced, or any chemical effect, 

 using the delicate test of solution of iodide of potassium and starch. 



In a few experiments on metallic conductors, the effect of the electricity of the 

 Torpedo on the galvanometer appeared to be much the same, whatever metals were 

 used, and whether rusty or bright, provided the junctions were bright. The mass 

 of metal appeared to have more influence ; the effect, as might have been expected, 

 diminishing with the increase of the mass ; thus, when a poker weighing about two 

 pounds formed a part of the circle, the effect on the electrometer, though distinct, 

 was less powerful than when it was omitted ; and when a large copper coal-scuttle 

 was substituted for it, the effect was still more diminished, the deviation of the 

 needle being only just visible. Extension of surface, as in the instance of increased 

 length of wire, had a sensible modifying effect ; thus, in an experiment in which 

 about 1000 feet of wire were used (formed of three pieces, two about V-^th of an inch 

 in diameter, the third piece considerably finer), the motion of the needle was decidedly 

 slower than when a short length of wire was employed, though the space traversed 

 was not perceptibly different. 



The few experiments which I have made on the Torpedo, analogous to those insti- 

 tuted by Mr. Todd, described by him in the Philosophical Transactions for 1816, 

 have afforded very similar results. When the brain has been divided longitudinally, 

 the fish has continued to give shocks ; when the brain has been entirely extracted, 

 the fish instantly lost this power, though the muscles generally continued to act 

 powerfully ; nor could any shock be procured in this instance, either by puncturing 

 with a sharp instrument the electrical nerves, where they quit the cavity of the cra- 

 nium, or where they enter the electrical organs, just after passing between the 

 branchial cartilages. On one occasion, however, it may be mentioned, that when a 

 small portion of brain was accidentally left, contiguous to the electrical nerves of 

 one side, and with which they were connected, then the fish, on being irritated, gave 

 a shock to an assistant who grasped the corresponding electrical organ. 



M. DE Humboldt states that the shock of the Torpedo may be procured by touch- 



