During his attendance upon the pontiff at Bologna Poggio enjoyed frequent opportunities of becoming thoroughly acquainted with the singular merits of Tommaso, whose proficiency in literature and ingenuous manners had some years before engaged his esteem, and conciliated his affection. Nor was Tommaso insensible of the good qualities of Poggio. A memorial of the mutual regard which subsisted between these able scholars, exists in the dedication of a Dialogue _On the Unhappiness of Princes_, which Poggio published in the year 1440, and which he inscribed to his friend before his virtues had been brought forward to public observation by his acquisition of distinguished honour and great emolument. In this dedication Poggio notices the common error of men, who are so much struck with the pomp and grandeur of the great, that they take it for granted, that power and magnificence confer on their possessors the gift of true felicity. He observes, however, that those who rise above the level of vulgar intellect ought to be convinced that happiness does not depend upon the external blessings of fortune, but that it is the meed of virtuous dispositions. He professes that it is his object to persuade men of this truth; and remarks that a work which is intended to promote this happy end, may with the strictest propriety be addressed to an ecclesiastic, who in the whole course of his conduct has demonstrated, that he has studied to be virtuous, rather than to be rich or great.[350] After this preface, Poggio proceeds to state, that in the summer of the year in which he followed Eugenius IV. to Florence, to which city the pontiff was banished by the fury of the Roman populace, he happened to pay a visit to Niccolo Niccoli, whose house was the common resort of the learned. Here he found Carlo Aretino and Cosmo de’ Medici, with whom he entered into conversation on the politics of Italy. After having recounted to his friends the hardships which he had lately suffered when he was taken captive by the soldiers of Piccinino, he complained of the unsettled life which he led in consequence of his attendance upon the Roman court, which in the course of thirty-four years that had elapsed since his admission into the pontifical chancery, had never continued for two years together in the same place. On this Carlo Aretino remarked, that Poggio was discontented with a situation which the generality of men regard as an object of envy, since the pontiffs and their superior servants are usually deemed masters of every circumstance necessary to the insurance of a happy life. In consequence of this observation, Niccolo Niccoli gave it as his opinion, that whatever advantages the attendants and courtiers of great potentates may derive from the control which they acquire over public affairs, princes themselves lead a life of anxiety and care, and endure all the inconveniences, whilst others reap all the benefits of empire. Such is the introduction to the Dialogue