To be in the front rank an artist must have acquired a vast knowledge of the technique of his art, and have a powerful imagination which has been highly cultivated. But the qualifications must be balanced. Commonly when this balance is not present the deficiency is in the imagination, but there are instances where, though the power of execution is supreme, the imagination has so far exceeded all bounds as to render this power of comparatively small practical value. The most conspicuous example of this want of balance is Lionardo, who accomplished little though he was scarcely surpassed in execution by Raphael or Michelangelo. His imagination invariably ran beyond his execution; his ideas were always above the works he completed or partly finished: he saw in fact far beyond anything he could accomplish, and so was never satisfied with the result of his labour. At the same time he was filled with ideas in the sciences, and investigated every branch of knowledge without bringing his conclusions to fruition. During the latter part of his life, Michelangelo showed a similar defect in a lesser degree, for his unfinished works of the period exceed in number those he completed. Naturally such intellectual giants, whose imaginations cannot be levelled with the highest ability in execution, are few, but the lesser luminaries who fail, or who constantly fail, in carrying out their conceptions, are legion, though they may have absorbed the limit of knowledge which they are capable of acquiring in respect of execution. It is common for a painter to turn out a few masterpieces and nothing else of permanent value. This was the case with numerous Italian artists of the seventeenth century, and it is indeed a question whether there is one of them, except perhaps Domenichino, whose works have not a considerable range in æsthetic value.