"Yes, but I thought he was spinning a yarn at the time."
"You were wrong, Willis; he likewise told us that sound travels at the rate of four hundred yards in a second."
"Well, but—"
"Have patience, Willis! When the lightning flashes, the electric spark is discharged, is it not?"
"Well, I was never high enough aloft to see."
"But others have been; Newton and Franklin have seen it. Now, if the sound reaches our ears a second after the flash, it has travelled four hundred yards. If we hear it twelve or thirteen seconds after, it has travelled twelve or thirteen times four hundred yards, or about half a mile, and so on."
"But what has that to do with your pulse?"
"In the first place, I am in perfect health, am I not?"
"I hope so, Master Jack."
"Then when our systems are in good order, the pulse, keeping fractions out of view, beats once in every second; and consequently, though we do not always carry a watch, we always have our arteries about us, and may therefore always reckon time."