To this period, too, belongs his avowedly theological pamphlet, _Notes on the Construction of Sheepfolds_. It is of 1851, attacks ecclesiastical pretensions on Scriptural grounds, and in spite of its sectarian limitations was considered so sound in its main drift that the author reissued it in his mature period. He states that all his works up to 1853 are marred by his narrow Protestant dogmatism. Now 1858, as we have seen, was his year of freedom from it, and from much that was more precious. Between 1853 and 1858 came out volumes iii and iv of _Modern Painters_, the _Lectures on Architecture and Painting_ at Edinburgh, and the lectures at Manchester on the _Political Economy of Art_. The last marks transition. It is the forerunner of the next period; it shows us how his way of treating Art led him on to Economics. But it is of great interest to study his position in these two volumes of _Modern Painters_. They are as religious as ever, and as devout; but between Catholic and Protestant, frequently brought into contrast, they hold the scales of judgment. The author casts the lantern of criticism impartially upon both, but his own faith in the great verities still holds. It is plain, however, that conduct was rising to the chief place in his mind. The Sermon on the Mount was becoming, what it ever afterwards remained to him, the central teaching of the Christian faith. If we omit the Poems of his boyhood and youth, and his early minor scientific contributions to journals, and begin his career as a writer for the public with the year 1842, when he wrote the first volume of _Modern Painters_, published next year, we have sixteen years of authorship for the Early Period. We have also, oddly enough, sixteen years of authorship, 1858 to 1874, for his Middle Period, shortly to be described; and if we give sixteen years for the mature period also, that brings us to 1890, only a few months after the last number of _Præterita_ struggled into the light from his failing pen. He wrote no more. We thus have three periods, Early, Middle, and Mature, each of sixteen years, not difficult to remember, 1842-1858, 1858-1874, and 1874-1890. It is a testimony to his utter frankness and undimmed candour that we are able thus to map out the growth of his convictions. For a growth it was, all the time, though apparently 1858 was a year of wreck and ruin. We cannot put new wine into old wineskins. His middle period was the time for the analytical tendency of his mind to have its way. Mazzini had already said that Ruskin had the most analytic mind in Europe; and now that searching analysis which had discovered Luini and placed Tintoretto, and had penetrated, by a way of its own, far into the hidden secret of Beauty, could not be denied when it faced the stronghold of the Christian revelation, even though his own heart and every fibre of his sensitive nature was within the fortress attacked.