Such a notion is not the pure matter of conjecture it may at first sight seem to be. Frederick was in relation with those who might well have put him in possession of this among other secrets. When the Tartars stormed the _Vulture’s Nest_, as it was called, in the Syrian castle of Alamout, they found an observatory well supplied with instruments of precision, and that of all kinds.[211] Now this place was the last refuge of the Assassins, that strange sect who owned obedience to the Old Man of the Mountain. Frederick II. when in the East paid these people a visit,[212] and again at Melfi, in his own dominions, he received their ambassadors and entertained them at a great banquet.[213] Considering then the Emperor’s well-known curiosity in all matters of physical science, we may feel sure he would profit by any improvements or discoveries the observers at Alamout could communicate. If the contrivance set up at Naples was really a _seismometer_, this would furnish a curious comment on Bacon’s statement that Michael Scot excelled in investigating the movements of matter.[214] Passing to what rests on more certain evidence, we find Scot’s fame in those days attested by one of his most distinguished contemporaries, and that in a way which makes him appear as an honoured master in the science of algebra, then lately introduced from the Moorish schools. This improvement and testimony were both of them due to a certain Leonardo of the Bonacci family of Pisa, who was, perhaps, the first to bring the new method of calculation to the knowledge of his countrymen. His father had been overseer of the customs at Bougie, in Barbary,[215] on behalf of the Pisan merchants who traded thither. Observing the superior way of reckoning used by the Moors in that country, he sent home for his son that the boy might be trained in this admirable way of counting. Leonardo perfected his art in after years by travel and study in Egypt, Syria, and Greece, as well as in Sicily and Provence. The ripe fruit of this knowledge saw the light in 1222, when he published for the first time his famous _Liber Abbaci_. It consisted of fifteen chapters, in which the author declared the secret of the Indian numerals as well as the fundamental processes of algebra.[216]