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

pairs; each pair in the same exact order, i. e., first a copper and then a zinc, and each pair separated from the next pair by the wet cloth, and the whole re- tained in a pile by three or four perpendicular glass rods. This pile is found to be charged with negative electricity at its lower extremity, which is copper, and with positive electricity at its top, which is zinc. The top and bottom ends of this series or pile are called the poles. As soon as the poles of the pile are united by a conducting wire, the water that moistens the cloth between the sev- eral pairs becomes decomposed, and hydrogen ris-8- voitaicPiio. is attracted to the copper, and the oxygen to the zinc. Then by this chemical action there is an electro-motive force set in action, which decomposes the natural or latent electricity of the metals into positive and negative electricity, the former ac- cumulating upon the zinc pole in this arrangement, and the latter upon the copper. This pile may be laid clown, or turned the other end up, — still is the zinc the positive pole, and the copper the negative. But here let me call particular atten- tion to the fact, that this is exactly the reverse of what obtains in all our metallic pairs in liquid batteries, — for then the cop- per is the positive, while the zinc is the negative pole ; but this can be easily explained. From this fact not being heeded a deal of confusion and misunderstanding has always resulted. The batteries with which we have to do, then, give the most oxi- dizable metal, which is zinc, as the negative pole; while the least oxidizable metal, which is copper, or silver, or platinum, is the positive pole; but in a moist or dry pile, the reverse is the result. Let these facts be retained. But to return. If the two poles of the voltaic pile be con- nected by a conducting wire, then the two opposite electricities travel towards each other over the same wire to neutralize where they started from, which is at the zinc or most oxidizable metal. But as there is a certain continuous supply, there will also be a continuous process or current as long and in propor-