"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."
Pedro accepted his explanation of the principle slowly.
"There must be some hidden defect in the device," he insisted. "Look around us. Nowhere does Nature employ the device you call the wheel. Observe the mechanism of the human body; observe the horse's frame; observe...."
"Observe that horse and man and waggon with its wheels are speeding from us," replied Luis, laughing. "Cannot you yield to accomplished facts? You tire me with your appeals to Nature. Has man ever accomplished anything worth having except by combating Nature? We do violence to her when we chop down a tree! I would go further than this invention of the waggon. Conceive a more powerful motive force than that horse...."
"Attach two horses to the waggon."