The reader will pardon this slight digression, and the writer makes the following assertion for the investigation of the curious, without any fear of a negative being produced. The conclusion is from many years of observation; viz., _That every thing in Nature of the Animal or the Vegetable kingdom; the Rainbow and the Elements; that all the works of Art embraced in the comprehensive term_, Architecture (Edificial or Naval): _in the Arch itself, and even in Mechanics; that in all these productions of Nature or Art there are_ ONLY THREE GRAND PARTS! And many of those parts contain within themselves _three_ subdivisions. Those subdivisions are only accessories, holding the same relation to the whole, that the secondary colours do to the primitives of the Rainbow. We will give a few illustrations from Nature and Art. For instance,--the Fruit-tree,--the three primitive parts are the roots, trunk, and branches, these are composed of fibrum, sap, and bark; the accessories are the leaves and fruit; the leaf consists of the stalk, fibres, and the web; the fruit, of the rind, the apple, and the core. The Human form will bear the same test; viz., head, trunk, and limbs--nay, the very principles of life, brain--lungs, and heart; and also the great combinations in Chemistry! The sublime science of Astronomy also supports the conclusion. For the illustration from Art--a Temple. The three grand divisions are the foundation, body, and roof; the front of the edifice is in three parts--viz., columns, entablature, and pediment; these being subdivided, and three parts again appear: 1st, a Column,--the shaft, capital, and abacus; 2d, the Entablature,--the architrave, frieze, and cornice; 3d, the Pediment,--the apex, and the two corners, forming a triangle. The triangle is, also, the facial characteristic of a square Pyramid, and its square base contains two triangles; but the true Pyramid contains only three sides, each, with the base, present triangles. If man's efforts in Art have produced by accident the TRIA JUNCTA IN UNO,-- we must feel that nothing in _Nature_ can be accidental, and investigation will prove that the Divine "three" pervade all! We are not aware that the above assertion has ever been made by any author, but we are convinced from years of observation, that although original and startling, it is no less the truth--for being founded in Nature it could not be otherwise. In the third volume this subject will be enlarged upon; for the present we claim the discovery of this great philosophical principle--the true active one of Nature and of Art, with the possession of which a man has the key to the _arcana_ of both. The Mexican Aborigines then had, apparently, no knowledge of the art of mixing colours, from which fact a strong proof is gained of their great antiquity.