Fig. 110
The engine had two cylinders. There were two batteries—one for each cylinder. Each battery consisted of five dry cells like the one represented in [Fig. 111].
"Now, why don't I feel the electricity when I touch the binding posts of this dry cell?" inquired one of the boys as he handled one of the cells which we had taken out. "Well, I'll give you two reasons why do you not feel it," said I. "First, because you were touching only one binding post at a time. You must touch both of the binding posts of the battery cell at the same time, so that the electric current may pass from one post to the other through your body. Second, even when you do touch both binding posts at the same time you feel no current, simply because you offered probably about 100,000 ohms of resistance to the passage of the current and inasmuch as the one cell exerts only 1.5 volts of pressure, it could send only about .0000015 of an ampere through you. This you cannot feel.
Fig. 111
(1.5 volts)/(100,000 ohms) = .0000015 amperes.
"I now connect my instrument as a volt meter between the binding posts of the cell and you see it indicates 1.5 volts, and when I connect it for an instant as an ammeter you see it indicates twenty amperes. That is twice as much as they use for executing criminals by electricity. So you see if you could reduce your resistance sufficiently this one battery cell might kill you. Some people have less resistance than others. The resistance of the body is chiefly in the outer skin. If one's hands are dry and his skin has been made tough and horny by hard work, he has many times the resistance of one whose hands are moist and whose skin is thin and tender.
"Suppose we select the tip of the tongue as the portion of the body which will offer the least resistance and will be most sensitive to slight electric currents. Let us then connect one dry cell with the ammeter and place the tip of the tongue between the bare ends of the wire at T ([Fig. 112]).