This decay of interest in speculative thought might be attributed to the decline of mental freshness and of hospitality to new ideas which often comes with advancing years, were it not that, in his case, there was no such decline.  On the contrary, as his interest in speculative thought gradually withered, his interest on the side of scholarship and linguistics became greater than ever, and his energy here was always seeking new outlets for itself.  When he was nearly sixty he began the study of Assyrian.  He did so in connection with his lectures on Apologetics,—­because he wanted to give his class some idea of the confirmation of the Scripture records, which he believed were to be found in the cuneiform inscriptions.  But ere long the study took possession of him.  His letters, and the little time-table diary of his daily studies, record the hours he devoted to it.  When he went to America he took his Assyrian books with him, and pored over them on the voyage whenever the Atlantic would allow him to do so.  And he was fully convinced that what interested him so intensely must interest his students too.  One of them, the Rev. J.H.  Leckie, thus describes how he sought to make them share in his enthusiasm:—­

“One day when we came down to the class, we found the blackboard covered with an Assyrian inscription written out by himself before lecture hour, and the zest, the joy with which he discoursed upon the strange figures and signs showed that, though white of hair and bent in frame, he was in the real nature of him very young.  For two days he lectured on this inscription with the most assured belief that we were following every word, and there was deep regret in his face and in his voice when he said, ’And now, gentlemen, I am afraid we must return to our theology.’"[20]

[Footnote 20:  Life and Letters, p. 743.]

Another of his students, referring to the same lectures, writes as follows:—­

“It was fine, and one loves him all the more for it, but it was exasperating too, with such tremendous issues at stake in the world of living thought, to see him pounding away at those truculent old Red Indians in their barbarian original tongue.  Yet I would not for much forget those days when we saw him escaping utterly from all worries and troubles and perfectly happy before a blackboard covered with amazing characters.  It was pure innocent delight in a new world of knowledge, like a child’s in a new story-book.”

When he was sixty-three he added Arabic to his other acquirements.  It is not quite clear whether he had in view any purpose in connection with his professional work beyond the desire to know the originals of all the authorities quoted in his lectures.  But, when he had sufficiently mastered the language to be able to read the Koran, he knew that he had two grounds for self-congratulation, and these were sufficiently characteristic.  One was that he had his revenge on Gibbon, who had described so triumphantly the career of the Saracens and who yet had not known a word of their language.  The other was that he was now able to pray in Arabic for the conversion of the Mohammedans.