Page:Experimental researches in electricity.djvu/51

Rh have little or no doubt that Harris's electrometer would show it (23, 95).

90. ii. Magnetism.—Perfectly distinct. According to Dr. Davy, the current deflected the needle and made magnets under the same law, as to direction, which governs currents of ordinary and voltaic electricity.

91. iii. Chemical decomposition.—Also distinct; and though Dr. Davy used an apparatus of similar construction with that of Dr. Wollaston (63), still no error in the present case is involved, for the decompositions were polar, and in their nature truly electro-chemical. By the direction of the magnet, it was found that the under surface of the fish was negative, and the upper positive; and in the chemical decompositions, silver and lead were precipitated on the wire connected with the under surface, and not on the other; and when these wires were either steel or silver, in solution of common salt, gas (hydrogen?) rose from the negative wire, but none from the positive.

92. Another reason for the decomposition being electro-chemical is, that a Wollaston's apparatus constructed with wires, coated by sealing-wax, would most probably not have decomposed water, even in its own peculiar way, unless the electricity had risen high enough in intensity to produce sparks in some part of the circuit; whereas the torpedo was not able to produce sensible sparks. A third reason is, that the purer the water in Wollaston's apparatus, the more abundant is the decomposition: and I have found that a machine and wire points which succeeded perfectly well with distilled water, failed altogether when the water was rendered a good conductor by sulphate of soda, common salt, or other saline bodies. But in Dr. Davy's experiments with the torpedo, strong solutions of salt, nitrate of silver, and superacetate of lead were used successfully, and there is no doubt with more success than weaker ones.

93. iv. Physiological effects.—These are so characteristic, that by them the peculiar powers of the torpedo and gymnotus are principally recognised.

94. v. Spark.—The electric spark has not yet been obtained, or at least I think not; but perhaps I had better refer to the evidence on this point. Humboldt, speaking of results obtained by M. Fahlberg, of Sweden, says, "This philosopher has seen an electric spark, as Walsh and Ingenhousz had done before him at London, by placing the gymnotus in the air, and interrupting the conducting chain by two gold leaves pasted upon