“Galvanism I have found, by numerous experiments, to be _a process purely chemical_, and to depend wholly on the oxidation of metallic surfaces, having different degrees of electric conducting power. “Zinc is incapable of decomposing _pure_ water; and if the zinc plates be kept moist with _pure_ water, the galvanic pile does not act; but zinc is capable of oxidating itself when placed in contact with water, holding in solution either oxygen, atmospheric air, or nitrous or muriatic acid, &c.; and under such circumstances the galvanic phenomena are produced, and their intensity is in proportion to the rapidity with which the zinc is oxidated. “The galvanic pile only acts for a few minutes, when introduced into hydrogen, nitrogen, or hydrocarbonate [the gas obtained by the action of steam on charcoal]; that is, only as long as the water between its plates holds some oxygen in solution; immerse it for a few moments in water containing air, and it acts again. “It acts very vividly in oxygen gas, and less so in the atmosphere. When its plates are moistened by marine acid, its action is very powerful, but infinitely more so when nitrous [nitric] acid is employed. Five plates with nitrous [nitric] acid gave sparks equal to those of the common pile. From twenty plates the shock was insupportable. “I had almost forgotten to mention, that charcoal is a good galvanic exciter, and decomposes water, like the metals, in the pile; but I must stop, without being able to expatiate on the connection which is now obvious between galvanism and some of the phenomena of organic motion.... “I remain with sincere respect and affection, yours “HUMPHRY DAVY.” To his mother he writes:-- “Hotwells, _November 19, 1800_. “MY DEAR MOTHER,--Had I believed that my silence of six weeks would have given you a moment’s uneasiness, I should have written long ago. But I have been engaged in my favourite pursuit of experimenting, and in endeavouring to amuse two of my friends who have spent some days at the Institute. One of them is your quondam lodger, Gregory Watt, who desired to be kindly remembered to you and the family....