the vacuum or minus-electrification, and must never lie on the patient higher than the other chain, but generally lower. The other chain must have one end of it turned in a ring: this is to touch the prime conductor with, in order to take the spark, and bring on the shock upon the patient; and it will come upon the patient in that part where the other end of the same chain is applied. This must be well understood, or mistakes will be made in passing the shocks - their directions will be wrong, and that will do essential damage in many particulars. Notice then, once for all, that the same chain that takes the spark or shock from the prime conductor, brings the shock upon the patient at whatever part it touches the patient: for instance, we will suppose that one end of the chain, which takes the spark from the machine, is held in the patient's right hand; and one end of the other chain, viz. the chain that connects with the leaden coating on the receiver, is held in the patient's left hand. if the shock is passed, it will fly from right hand to left, in the straightest and nighest passage that can be found through the breast. The chain that brings on the shock, I have named plus-conveyance, because it conveys the plus-electrification, in the receiver, to the patient. The other I call evacuant, because it evacuates the plus-electrification, or shock, from the patient, at whatever part it is applied.

I hope, by this time, any one will fully understand how to direct the shock, according to the rules taught throughout the whole of chap. 3d. By means of two chains, and understanding their distinct offices, you will be able to observe all the rules prescribed for directing the shocks. You may pass the shock through the joint of a finger only, by laying the plus-conveyance on the one side, and the evacuant on the other; or place the plus-conveyance on the head or neck, and the evacuant on the feet, and the shock will fly from head or neck to the feet.

The electrometer is an artificial measurement of the quantity of the charge, in any particular receiver; but the quantity or charge is greater or less, according to the bigness of the receiver; and the electrometer only exhibits to your view the degree of charge, in any individual receiver. The little cork-balls, in the electrometer, as the machine charges, condense round themselves, globular atmospheres; the atmospheres increase as the machine charges; and as the atmospheres increase, the balls are separated by their own atmospheres. When the machine charges freely, the balls may be propelled to a horizontal plain; and if there is no body intervening, to affect the natural attitude of their atmospheres, they cannot be altered by an increase of the charge from that horizontal position. If any body less electrified approaches the globules of the electrometer, it

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