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

other must be as freely dissipated without hinderance, and if this point is well attended to, the power and uniformity of the machine will be greatly enhanced. The dry wall or chimney of the house is not always sufficient. A large copper wire leading to the moist earth, or connected with a water pipe, or gas pipe, by good metallic contact, is the most reliable. But, of course, where we wish to employ both electricities at once, we must not make either the rubber or the prime conductor communicate with the ground, but rather keep all well insulated. In every case the electricity is set free on the surface of the rubbed glass plate, or cylinder, the negative flying to the rubber, while the positive accumulates upon the glass, which induces it also by sharp points in the prime conductor ; and from here we can accumulate even greater quantities still by means of Leyden jars. The power of the jar is in proportion to the size; i. e., a half gallon jar is twice as powerful as a quart jar, if each is fully charged; for the for- mer will receive twice as many turns of the machine to charge it. If the outside tin foil coverings of two or more of these jars are put in communication, as, for instance, if set upon a sheet of tin foil, and at the same time the metal stems that communicate with the inner lining foil are joined also as by a chain, they thus become by this double connection as one jar, and can be charged and discharged through any one alone. This is called a battery of friction electricity. Thus the inner coat of the jar receives positive electricity from the prime conductor, while negative electricity is then always accumulated on the outside of the jar, or conductor that leads it off. Now, if a communication is made between the inner and the outer coatings of the jar directly, as by means of a discharge, or indirectly, as through the human body, a neutral- ization of the two electricities takes place with a loud crack and flash. If the negative charge is required, the prime conductor must communicate with the outer covering of the jar, &c.; but visually it is the positive charge that we have to do with. If the jar is discharged through the human body, there is a violent,