"Come," he said at length. "Let us drink success to the TACHYPOMP." "The TACHYPOMP?" "Yes. Why not? _Tachu_, quickly, and _pempo, pepompa_ to send. May it send you quickly to your wedding-day. Abscissa is yours. It is done. When shall we start for the prairies?" "Where is it?" I asked, looking in vain around the room for any contrivance which might seem calculated to advance matrimonial prospects. "It is here," and he gave his forehead a significant tap. Then he held forth didactically. "There is force enough in existence to yield us a speed of sixty miles a minute, or even more. All we need is the knowledge how to combine and apply it. The wise man will not attempt to make some great force yield some great speed. He will keep adding the little force to the little force, making each little force yield its little speed, until an aggregate of little forces shall be a great force, yielding an aggregate of little speeds, a great speed. The difficulty is not in aggregating the forces; it lies in the corresponding aggregation of the speeds. One musket-ball will go, say a mile. It is not hard to increase the force of muskets to a thousand, yet the thousand musket-balls will go no farther, and no faster, than the one. You see, then, where our trouble lies. We cannot readily add speed to speed, as we add force to force. My discovery is simply the utilization of a principle which extorts an increment of speed from each increment of power. But this is the metaphysics of physics. Let us be practical or nothing. "When you have walked forward, on a moving train, from the rear car, toward the engine, did you ever think what you were really doing?" "Why, yes, I have generally been going to the smoking-car to have a cigar." "Tut, tut--not that! I mean, did it ever occur to you on such an occasion, that absolutely you were moving faster than the train? The train passes the telegraph poles at the rate of thirty miles an hour, say. You walk toward the smoking-car at the rate of four miles an hour. Then _you_ pass the telegraph poles at the rate of thirty-four miles. Your absolute speed is the speed of the engine, plus the speed of your own locomotion. Do you follow me?" I began to get an inkling of his meaning, and told him so.