The most popular of his art criticisms are _St. Mark's Rest_ and _Mornings in Florence_, which are widely used as guidebooks, and which may be postponed until the happy time when, in Venice or Florence, one may read them to best advantage. Meanwhile, in _Seven Lamps of Architecture_ or _Stones of Venice_ or the first two volumes of _Modern Painters_, one may grow acquainted with Ruskin's theory of art. [Sidenote: HIS THEORY OF ART] His fundamental principle was summarized by Pope in the line, "All nature is but art unknown to thee." That nature is the artist's source of inspiration, that art at its best can but copy some natural beauty, and that the copy should be preceded by careful and loving study of the original,--this was the sum of his early teaching. Next, Ruskin looked within the soul of the artist and announced that true art has a spiritual motive, that it springs from the noblest ideals of life, that the moral value of any people may be read in the pictures or buildings which they produced. A third principle was that the best works of art, reflecting as they do the ideals of a community, should belong to the people, not to a few collectors; and a fourth exalted the usefulness of art in increasing not only the pleasure but the power of life. So Ruskin urged that art be taught in all schools and workshops, and that every man be encouraged to put the stamp of beauty as well as of utility upon the work of his hands; so also he formulated a plan to abolish factories, and by a system of hand labor to give every worker the chance and the joy of self-expression. [Sidenote: THEORY OF ECONOMICS] In his theory of economics Ruskin was even more revolutionary. He wrote several works on the subject, but the sum of his teaching may be found in _Unto This Last_; and the sum is that political economy is merely commercial economy; that it aims to increase trade and wealth at the expense of men and morals. "There is no wealth but life," announced Ruskin, "life including all its power of love, of joy and of admiration." And with minute exactness he outlined a plan for making the nation wealthy, not by more factories and ships, but by increasing the health and happiness of human beings. Three quarters of a century earlier Thomas Jefferson, in America, had pleaded for the same ideal of national wealth, and had characterized the race of the nations for commercial supremacy as a contagion of insanity. Jefferson was called a demagogue, Ruskin a madman; but both men were profoundly right in estimating the wealth of a nation by its store of happiness for home consumption rather than by its store of goods for export. They were misunderstood because they were too far in advance of their age to speak its trade language. They belong not to the past or present, but to the future. [Sidenote: FOR YOUNG READERS]