This is neither the time nor place to speak of the misfortunes that chequered his life. It will be sufficient to say that, in all he did, he at the time of doing it believed himself justified to his own conscience; while the various ills of poverty and loss of friends brought home to him the sad realities of life. Physical suffering had also considerable influence in causing him to turn his eyes inward; inclining him rather to brood over the thoughts and emotions of his own soul, than to glance abroad, and to make, as in Queen Mab, the whole universe the object and subject of his song. In the Spring of 1815 an eminent physician pronounced that he was dying rapidly of a consumption; abscesses were formed on his lungs, and he suffered acute spasms. Suddenly a complete change took place; and though through life he was a martyr to pain and debility, every symptom of pulmonary disease vanished. His nerves, which nature had formed sensitive to an unexampled degree, were rendered still more susceptible by the state of his health.
As soon as the Peace of 1814 had opened the Continent, he went abroad. He visited some of the more magnificent scenes of Switzerland, and returned to England from Lucerne by the Reuss and the Rhine. This river-navigation enchanted him. In his favorite poem of [Southey's]Thalaba, his imagination had been excited by a description of such a voyage. In the summer of 1815, after a tour along the southern coast of Devonshire and a visit to Clifton, he rented a house on Bishopgate Heath, on the borders of Windsor Forest, where he enjoyed several months of comparative health and tranquil happiness. The later summer months were warm and dry. Accompanied by a few friends, he visited the source of the Thames, making a voyage in a wherry from Windsor to Cricklade. His beautiful stanzas in the churchyard of Lechlade were written on that occasion. Alastor was composed on his return. He spent his days under the oak-shades of Windsor Great Park; and the magnificent woodland was a fitting study to inspire the various descriptions of forest scenery we find in the poem.
None of Shelley's poems is more characteristic than this. The solemn spirit that reigns throughout, the worship of the majesty of nature, the broodings of a poet's heart in solitude -- the mingling of the exulting joy which the various aspect of the visible universe inspires with the sad and struggling pangs which human passion imparts -- give a touching interest to the whole. The death which he had often contemplated during the last months as certain and near he here represented in such colours as had, in his lonely musings, soothed his soul to peace. The versification sustains the solemn spirit which breathes throughout: it is peculiarly melodious. The poem ought rather to be considered didactic than narrative: it was the outpouring of his own emotions, embodied in the purest form he could conceive, painted in the ideal hues which his brilliant imagination inspired, and softened by the recent anticipation of death.