Also the man will have joy, because it is given him to share the high, marvelous adventure of being. To the pleasures of the body there is a limit, and it comes quickly; but the pleasures of the mind are infinite, and no one who truly understands them can have a moment of boredom in life. To a man who possesses the key to modern thought, who knows what knowledge is and where to look for it, the life of the mind is a panorama of delight perpetually unrolled before him. To the minds of our ancestors there was one universe; but to our minds there are many universes, and new ones continually discovered. The only question is, which one will you choose? Will you choose the universe of outer space, the material world of infinity? Consider the smallest insect that you can see, crawling upon the surface of the earth; small as that insect is in relation to the earth, it is not so small, by millions of times, as is the earth in relation to the universe made visible to our eyes by the high-power telescope, plus the photographic camera, plus the microscope. If you want to know the miracles of this world of space, read Arrhenius' "The Life of the Universe," or Simon Newcomb's "Sidelights on Astronomy." Suffice it here to say that we have a chemistry of the stars, by means of the spectroscope; that we can measure the speed and direction of stars by the same means; that we have learned to measure the size of the stars, and are studying stars which we cannot even see! And then along comes Einstein, with his theories of "relativity," and makes it seem that we have to revise a great part of this knowledge to allow for the fact that not merely everything we look at, but also we ourselves, are flying every which way through space! Or will you choose the universe of the atom, the infinity of the material world followed the other way, so to speak? Big as is the universe in relation to our world, and big as is our world in relation to the insect that crawls on it, the insect is bigger yet in relation to the molecules which compose its body; and these in turn are millions of millions of times bigger than the atoms which compose them; and then, behold, in the atom there are millions of millions of electrons--tiny particles of electric energy! We cannot see these infinitely minute things, any more than we can see the electricity which runs our trolley cars; but we can see their effects, and we can count and measure them, and deal with them in complicated mathematical formulas, and be just as certain of their existence as we are of the dust under our feet. If you wish to explore this wonderland, read Duncan's "The New Knowledge," or Dr. Henry Smith Williams' "Miracles of Science."