This drawing originally appeared in Charles Kite's An Essay on the
Recovery of the Apparently Dead (London, 1788). The Bakken Library and Museum website describes the device and the theory (and practice!) behind it:
An electrostatic generator charges a Leyden jar capacitor, which can discharge its accumulated electrical energy through the electrodes below. Energy willbuild up until the voltage is high enough to jump the spark gap ab.
In 1788 Charles Kite, a member of the Royal Humane Society of London (an organization devoted to salvaging persons seemingly dead) described the use of electricity to revive a three-year-old child who was taken for dead after falling out of a window.
An "apothecary" was sent for, who could do nothing; then electrical resuscitation was attempted by a Mr. Squires, who
with the consent of the parents, very humanely tried the effects of electricity. Twenty minutes had at least elapsed before he could apply the shock, which he gave to various parts of the body without any apparent success; but at length, on transmitting a few shocks through the thorax, he perceived a small pulsation; soon after the child began to breathe, though with great difficulty. In about ten minutes she vomited. A kind of stupor remained for some days; but the child was restored to perfect health and spirits in about a week.
Do [these examples] not plainly point out, that electricity is the most powerful stimulus we can apply? ... And are we
not justified in assuming, that if it is able so powerfully to excite the action of the external muscles, that it will be capable of reproducing the motion of the heart, which is infinitely more irritable, and by that means accomplish our great desideratum, the renewal of the circulation?
There is some dispute among modern medical historians as to whether the child's heart had really stopped before the electricity was applied, but the intention was certainly to defibrillate her, and that is what Kite and others clearly believed Squires had done.