The royal tongue of the Aztecs is the only one now in existence that is based upon natural philosophy and the laws of sound. It appeals both to the eye and ear of the speaker, and thus the nicest shades of thought may be clearly expressed. There is no such thing as _stilted_ language amongst them, and logomachy is unknown. And here I may be permitted to observe that a wider field for research and discovery lies open in the domain of _sound_ than in any other region of science. The laws of harmony, even, are but imperfectly understood, and the most accomplished musicians are mere tyros in the great science of acoustics. There is every reason to believe that there is an intimate but yet undiscovered link between _number_, _light_, and _sound_ whose solution will astonish and enlighten the generations that are to succeed our own. _When God spake the worlds into being, the globular form they assumed was not accidental, nor arbitrary, but depended essentially upon the tone of the great Architect, and the medium in which it resounded._ Let the natural philosophers of the rising generation direct their especial attention toward the fields I have indicated, and the rewards awaiting their investigations will confer upon them immortality of fame. There is a reason why the musical scale should not mount in whole tones up to the octave; why the mind grasps decimals easier than vulgar fractions, and why, by the laws of light, the blood-red tint should be heavier than the violet. Let Nature, in these departments, be studied with the same care that Cuvier explored the organization of insects, that Liebig deduced the property of acids, and that Leverrier computed the orbit of that unseen world which his genius has half created, and all the wonderful and beautiful secrets now on the eve of bursting into being from the dark domain of sound, color, and shape, will at once march forth into view, and take their destined places in the ranks of human knowledge. Then the science of computation will be intuitive, as it was in the mind of Zerah Colburn; the art of music creative, as in the plastic voices of Jehovah; and the great principles of light and shape and color divine, as in the genius of Swedenborg and the imagination of Milton. I have now completed the outline of the sketch, which in the foregoing pages I proposed to lay before the world. The peculiar circumstances which led me to explore the remains of the aboriginal Americans, the adventures attending me in carrying out that design, the mode of my introduction into the Living City, spoken of by Stephens, and believed in by so many thousands of enlightened men, and above all, the wonderful and almost incredible character of the people I there encountered, together with a rapid review of their language and literature, have been briefly but faithfully presented to the public.