Page:Experimental researches in electricity.djvu/59

Rh of the arrangements, and the following more unexceptionable form of experiment was adopted.

119. Tin vessels were formed, five inches deep, one inch and a quarter wide in one direction, of different widths from three-eighths to five-eighths of an inch in the other, and open at one extremity. Into these were fixed by corks, plates of platina, so that the latter should not touch the tin cases; and copper wires having previously been soldered to the plates, these were easily connected, when required, with a voltaic pile. Then distilled water, previously boiled for three hours, was poured into the vessels, and frozen by a mixture of salt and snow, so that pure transparent solid ice intervened between the platina and tin: and finally these metals were connected with the opposite extremities of the voltaic apparatus, a galvanometer being at the same time included in the circuit.

120. In the first experiment, the platina pole was three inches and a half long, and seven-eighths of an inch wide; it was wholly immersed in the water or ice, and as the vessel was four-eighths of an inch in width, the average thickness of the intervening ice was only a quarter of an inch, whilst the surface of contact with it at both poles was nearly fourteen square inches. After the water was frozen, the vessel was still retained in the frigorific mixture, whilst contact between the tin and platina respectively was made with the extremities of a well-charged voltaic battery, consisting of twenty pairs of four-inch plates, each with double coppers. Not the slightest deflection of the galvanometer needle occurred.

121. On taking the frozen arrangement out of the cold mixture, and applying warmth to the bottom of the tin case, so as to melt part of the ice, the connection with the battery being in the meantime retained, the needle did not at first move; and it was only when the thawing process had extended so far as to liquefy part of the ice touching the platina pole, that conduction took place; but then it occurred effectually, and the galvanometer needle was permanently deflected nearly 70°. 122. In another experiment, a platina spatula, five inches in length and seven-eighths of an inch in width, had four inches fixed in the ice, and the latter was only three-sixteenths of an inch thick between one metallic surface and the other; yet this arrangement insulated as perfectly as the former.

123. Upon pouring a little water in at the top of this vessel on the ice, still the arrangement did not conduct; yet fluid water was evidently there. This result was the consequence