Two years later George Wilson, who was now a professor in the University, had the satisfaction of intimating to his friend that his _alma mater_ had conferred on him the degree of D.D., and in the following year (1859) a much higher honour was placed within his reach. The Principalship of the University became vacant by the death of Dr. John Lee, and the appointment to the coveted post, like that to the two professorships, was in the hands of the Town Council. It was informally offered to Cairns through one of the councillors, but again he sent a declinature, and again he kept the matter carefully concealed. It was not, in fact, until after his death, when the correspondence regarding it came to light, that even his own brothers knew that at the age of forty this great and dignified office might have been his. These declinatures on Cairns's part of philosophical posts, or posts the occupation of which would give him time and opportunity for doing original work in philosophy, are not on the whole difficult to understand when we bear in mind his point of view. He had, after careful deliberation, given himself to the Christian ministry, and he meant to devote the whole of his life to its work. He was not to be turned aside from it by the attractions of any employment however congenial, or of any leisure however splendid. His speculative powers had been consecrated to this object, as well as his active powers, and would find their natural outlet in harmony with it. And so the hopes of his friends and his own aspirations must be realised in his work, not in the field of philosophy but in that of theology. Accordingly, he decided to follow up his work in the periodicals by writing a book. He took for his subject "The Difficulties of Christianity," and made some progress with it, getting on so far as to write several chapters. Then he was interrupted and the work was laid aside. The great book was never written, nor did he ever write a book worthy of his powers. A moderate-sized volume of lectures on "Unbelief in the Eighteenth Century," a volume of sermons, most of which were written in the first fifteen years of his ministry, a Memoir of Dr. Brown,--these, with the exception of a quantity of pamphlets, prefaces, and magazine articles, were all that he gave to the world after the time with which we are now dealing. How are we to account for this? The time in which he lived was a time of great intellectual activity and unsettlement--time that, in the opinion of most, needed, and would have welcomed, the guidance he could have given; and yet he stayed his hand. Why did he do so? This is the central problem which a study of his life presents, and it is one of no ordinary complexity; but there are some considerations relating to it which go far to solve it, and these it may be worth while for us at this point to examine.