Each one took a hand at trying to start the boat, but although she had acted perfectly well the day before, on this morning no one could get a single explosion. The switch was closed. The gasolene was turned on. The carburetor valves were set at the mark. The spark coils responded with their familiar buzz. She had been primed and, when she had refused to respond to this treatment, the pet valves were opened and the wheel rolled over several times to sweep out the cylinders. But absolutely nothing moved her--neither coaxing nor gibes. Suddenly some one rolled the wheel over for the five-hundredth time and she started and behaved well all day. All this would not have given us the slightest aggravation if we could only have found out what was the matter and what it was we finally did to correct it. But this we shall probably never know, and hence we are worshippers of the motor boat while we continue to distrust it and complain of it. While the boat was running one of the boys noticed that a binding post at the end of one of the spark plugs seemed to be loose. He inadvertently put out his hand to tighten it and received a terrific shock. This raised the question among the boys, why one gets a shock from some of the binding posts in the electrical equipment but not from others. I suggested that we run in and call at the house to get my portable measuring instrument (Fig. 110) and a little lunch, and then go up to the upper end of the lake and take our time in examining the electrical equipment of the boat. [Illustration: 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. [Illustration: Fig. 111] (1.5 volts)/(100,000 ohms) = .0000015 amperes.