Page:My Airships.djvu/16

 barn door, loaded it with sacks of maize, and hauled in one load what ten horses could not have brought on their backs. True, it required seven horses to drag it, while five men had to sit around its edges and hold the load from falling off." "What would you have?" answered Pedro. "Nature demands compensations. You cannot get something from nothing or more from less !" "If we could put rollers under the drag, less pulling power would be needed."

"Bah ! the force saved would be used up in the labour of shifting the rollers." "The rollers might be attached to the drag at fixed points by means of holes running through their centres," mused Luis. " Or why should not circular blocks of wood be fixed at the four corners of the drag ? . . . Look, Pedro, yonder along the road. What is coming ? The very thing I imagined, only better ! One horse is pulling it at a good trot!" The first waggon to appear in that region of the interior stopped, and its driver spoke with the boys. "These round things ?" he answered to their questions; "they are called wheels."