And here Mr. Joslyn went into a long mathematical talk, with which I will not harass the reader, perfectly sure, from other experiments which I have tried with other readers, that this reader would skip it all if it were written down. Stated very briefly, it amounted to this: In the old-fashioned experiments of those days, a cannon-ball travelled four thousand and one hundred feet in nine seconds. Now, Joslyn was convinced, like every other engineman I ever talked to, that on a steep down-grade he could drive a train at the rate of a hundred miles an hour. This is thirteen hundred and fourteen feet in nine seconds,--almost exactly one-third of the cannon-ball's velocity. At those rates, if the valley at Chamoguin were really but five-eighths of a mile wide, the cannon-ball would cross it in seven or eight seconds, and the train in about twenty-three seconds. Both Todhunter and Joslyn were good enough mechanics and machinists to know that the rate for thirty-three hundred feet, the width of the valley, was not quite the same as that for four thousand feet; for which, in their book, they had the calculations and formulas; but they also knew that the difference was to their advantage, or the advantage of the bold experiment which had occurred to both of them when Todhunter had made on the tender his very critical suggestion. The reader has already conceived the idea of this experiment. These rash men were wondering already whether it were not possible to leap an engine flying over the Chamoguin ravine, as Eclipse or Flying Childers might have leaped the brook at the bottom of it. Joslyn believed implicitly, as I found in talk with him, the received statement of conversation, that Eclipse, at a single bound, sprang forty feet. "If Eclipse, who weighed perhaps one thousand two hundred, would spring forty feet, could not my train, weighing two hundred tons, spring a hundred times as far?" asked he triumphantly. At least, he said that he said this to Todhunter. They went into more careful studies of projectiles, to see if it could or could not. The article on "Gunnery" gave them just one of those convenient tables which are the blessing of wise men and learned men, and which lead half-trained men to their ruin. They found that for their "range," which was, as they supposed, eleven hundred yards, the elevation of a forty-two pounder was one degree and a third; of a nine- pounder, three degrees. The elevation for a railway train, alas! no man had calculated. But this had occurred to both of them from the beginning. In descending the grade, at the spot where, on his little map, Joslyn made the more westerly X, they were more than eleven hundred feet above the spot where he had made his second, or easterly X. All this descent was to the advantage of the experiment. A gunner would have said that the first X "commanded" the second X, and that a battery there would inevitably silence a battery at the point below.