"You have done well, youngster," he congratulated his helper, as he began to take off his protective covering, "Without your aid I could not have accomplished nearly this much during one period of labor. The periods of exercise and of relaxation are at hand--let us return to the house of Orlon, where we all shall gather to relax and to refresh ourselves for the labors of tomorrow." "But it's almost done!" protested Seaton. "Let's finish it up and shoot a little juice through it, just to try it out." "There speaks the rashness and impatience of youth," rejoined the scientist, calmly removing the younger man's suit and leading him out to the waiting airboat. "I read in your mind that you are often guilty of laboring continuously until your brain loses its keen edge. Learn now, once and for all, that such conduct is worse than foolish--it is criminal. We have labored the full period. Laboring for more than that length of time without recuperation results in a loss of power which, if persisted in, wreaks permanent injury to the mind; and by it you gain nothing. We have more than ample time to do that which must be done--the fifth-order projector shall be completed before the warning torpedo shall have reached the planet of the Fenachrone--therefore over-exertion is unwarranted. As for testing, know now that only mechanisms built by bunglers require testing. Properly built machines work properly." "But I'd have liked to see it work just once, anyway," lamented Seaton as the small airship tore through the air on its way back to the observatory. "You must cultivate calmness, my son, and the art of relaxation. With those qualities your race can easily double its present span of useful life. Physical exercise to maintain the bodily tissues at their best, and mental relaxation following mental toil--these things are the secrets of a long and productive life. Why attempt to do more than can be accomplished efficiently? There is always tomorrow. I am more interested in that which we are now building than you can possibly be, since many generations of the Rovol have anticipated its construction; yet I realize that in the interest of our welfare and for the progress of civilization, today's labors must not be prolonged beyond today's period of work. Furthermore, you yourself realize that there is no optimum point at which any task may be interrupted. Short of final completion of any project, one point is the same as any other. Had we continued, we would have wished to continue still farther, and so on without end." "You're probably right, at that," the impetuous chemist conceded, as their craft came to earth before the observatory. * * * * *