103. Eminently deficient in works representative of the earliest and purest tendencies of art, our National Gallery nevertheless affords a characteristic and sufficient series of examples of the practice of the various schools of painting, after oil had been finally substituted for the less manageable glutinous vehicles which, under the general name of tempera, were principally employed in the production of easel pictures up to the middle of the fifteenth century. If the reader were to make the circuit of this collection for the purpose of determining which picture represented with least disputable fidelity the first intention of its painter, and united in its modes of execution the highest reach of achievement with the strongest assurance of durability, we believe that--after hesitating long over hypothetical degrees of blackened shadow and yellowed light, of lost outline and buried detail, of chilled luster, dimmed transparency, altered color, and weakened force--he would finally pause before a small picture on panel, representing two quaintly dressed figures in a dimly lighted room--dependent for its interest little on expression, and less on treatment--but eminently remarkable for reality of substance, vacuity of space, and vigor of quiet color; nor less for an elaborate finish, united with energetic freshness, which seem to show that time has been much concerned in its production, and has had no power over its fate. 104. We do not say that the total force of the material is exhibited in this picture, or even that it in any degree possesses the lusciousness and fullness which are among the chief charms of oil-painting; but that upon the whole it would be selected as uniting imperishable firmness with exquisite delicacy; as approaching more unaffectedly and more closely than any other work to the simple truths of natural color and space; and as exhibiting, even in its quaint and minute treatment, conquest over many of the difficulties which the boldest practice of art involves.