The affairs of State did not prevent Avicenna from carrying on his studies, for during his stay at Hamadan he found time to commence his exposition of the philosophy of Aristotle entitled the "Shifa" which he undertook at the Sultan's request. At this time Avicenna presented the rare spectacle of a philosopher discharging the functions of a statesman, without injury to either statesmanship or philosophy. His great physical energy enabled him to spend the day in the service of the Sultan and a great part of the night in philosophical discussions with his disciples. His writings, which date from this time, allow us to judge with what success he pursued his philosophical studies, and we have every reason to believe that he was equally successful in the conduct of affairs, for, after the death of Shams-ed-Dawla, his son and successor Taj-ed-Dawla requested him to retain the post of vizier. Avicenna appreciated this testimony to his worth, but declined the offer in order to devote himself to the completion of his great work, the Shifa. But even in his studious retirement he was not out of reach of political disturbance. Suspected of carrying on secret correspondence with Ala-ed-Dawla, the governor of Ispahan, an enemy of Taj-ed-Dawla, Avicenna was imprisoned in a neighbouring fortress. He would probably have remained there a long time had not the fortune of war put Ala-ed-Dawla in possession of Hamadan, Avicenna was liberated after an imprisonment of four months. Despite this misadventure he succeeded during his stay at Hamadan in completing the Shifa and several medical treatises, besides, a little mystical allegory, "Hay ibn Yokdhan" ("The living one, son of the Waking One"). This shows the mystical side of Avicenna's philosophy, and we therefore subjoin an abridgment and explanation of it. "During my sojourn in a certain country, I used to make excursions with my friends to pleasant spots in our vicinity. One day when strolling out with them I met an old man who, in spite of his advanced age, seemed brimful of juvenile ardour, being neither bent nor having white hairs. We felt attracted by him and accosted him. After the usual salutations, I opened the conversation by requesting him to inform us about himself, his trade, name, family, and country. 'As to my name and family,' he answered, 'I am called Hay ibn Yokdhan, and I was born in Jerusalem; as to my occupation, it consists in traversing all the regions of the earth, always following the direction indicated by my Father. He has entrusted to me the keys of all the sciences and guided me through all ways even to the utmost bounds of the universe.' We continued to ask him questions regarding different branches of science till we touched on the science of physiognomy, on which he spoke with marvellous precision, taking it as the starting point of a discourse which he delivered to us."