Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

tion as the chemical action continues. Hence it results that the power of this pile is variable; it begins to diminish from the moment it is laid up, and in a short time it totally ceases, — the copper disks having been covered with hydrogen together with oxide of zinc, from the decomposition of sulphate zinc, while the zinc disks arc also loaded with their own oxide. This was a great inconvenience; besides, it gave the widest variety of results. To avoid this trouble it was proposed to substitute for these disks a trough of liquid ; and this necessarily converted the arrangement into a horizontal succession, instead of a perpen- dicular pile. The disks or plates were then to be rectangular, in the place of being circular; each two dissimilar metal pairs were to be in contact, and the whole series to be wedged tightly in the wooden trough, and so adjusted that they formed cells, and could be filled with the acidulated water in the trough at pleasure. This improvement was first pointed out by M. Cruik- shank, and was then arranged for and given by the Emperor Napoleon to the great Polytechnic School of France. It was with this battery that MM. Gay-Lussac and Thdnard, in 1808, made their splendid experiments; yet this cell trough was almost as troublesome as the original pile, but it possessed the advantage of more uniform and greater power ivhen cleaned and put together anew for work. Cruiksha>ik''s battery was then improved in various ways, until the cells of the trough were made to receive two plates of dis- similar metals, as before, it is true, but not of the same pair; i. e., one plate of a pair was in one cell, while the other plate was in the next cell, yet so as to be lifted out or put. in, so that every cell received a pair .of copper and zinc in the same liquid, not in metallic contact between themselves, as in the original, but connecting only with its next neighbor. This is the true arrangement of a galvanic battery as first shown by Becquerel. The author saw the remains of such a battery, which was pro- vided for Sir H. Davy, in the laboratory of the Museum build- ing of the Royal College of Physicians and Surgeons in London. Although only some eight or ten cells were in each trough, yet