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.

385. 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
connexion with the battery being in the mean time 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°.

386. 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.

387. 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 of the cold metals having frozen the water
where they touched it, and thus insulating the fluid part; and it well
illustrates the non-conducting power of ice, by showing how thin a film
could prevent the transmission of the battery current. Upon thawing parts
of this thin film, at _both_ metals, conduction occurred.