In that poem Virgil combines something of the spirit of the older or primitive type of didactic poetry with the systematic treatment of their subject employed by the Alexandrine Metaphrastae. He retains the old form of a personal address, not only in the dedication of the poem to Maecenas, but in the manner in which he inculcates his precepts on the husbandman, or indicates what he himself would do in particular circumstances(281). Yet he bears more resemblance to the poets of Alexandria in his systematic treatment and arrangement of his materials. He aims, like them, at communicating a large body of unfamiliar knowledge, as well as conveying practical precepts founded on experience. By combining these two aims, but much more by making the aims of conveying precept and instruction altogether subsidiary to that of moving the imagination and the affections, Virgil, if he has not created a new type of didactic poetry, has at least produced almost the only specimen of it which the world cares to read. He is apparently conscious of the difficulty of imparting to a poem of this type a continuous poetical charm; as Lucretius, with more reason, is conscious of the difficulty of securing a sustained poetical interest for his argumentative processes and his investigations into the first principles of things. Virgil's difficulty is to maintain his subject on the level of poetical feeling, while at the same time adhering to the necessities of practical instruction. And this difficulty attaches to every kind of didactic poetry. He had to associate with a poetic charm, not only the fair results of the husbandman's labour, the 'heavy harvests and the Massic juice of the vine,' but the processes and mechanical appliances through which these fair results were obtained. Although his idea of his art did not demand an exhaustive treatment of all the operations of rural industry, such as was demanded of the prose writers on the subject, yet it did demand that, in making his selection, he should regard the importance of each topic in connexion with the work of the farm as well as its adaptation to poetic treatment. It cannot be denied that this necessary infusion of prosaic matter deprives even the most perfect specimen of didactic poetry of that purity of imaginative interest which pervades the masterpieces of epic, lyrical, and dramatic genius: but it is, on the other hand, a great triumph of art to have redeemed so much as Virgil has done from the homely realities of life into the more sacred ground of poetry, and that without sacrifice either of the truth of fact or of the dignity and sobriety of expression.