And yet the popular idea of his inability to distinguish between a good student and a bad one was quite wrong.  He was not so simple as he seemed.  All who have sat in his classroom remember times when a sudden keen look from him showed that he knew quite well when liberties were being attempted with him, and gave rise to the uncomfortable suspicion that, as it was put, “he could see more things with his eyes shut than most men could see with theirs wide open.”  The fact is, that all his leniency with his students, and all his apparent ascription to them of a high degree of diligence, scholarship, and mental grasp, had their roots not in credulity but in charity—­the charity which “believeth all things, hopeth all things, endureth all things.”  His very defects came from an excess of charity, and one loved him all the better because of them.  Hence it came about that his students got far more from contact with his personality than they got from his teaching.  It is not so much his lectures as his influence that they look back to and that they feel is affecting them still.

When Dr. Cairns came to Edinburgh from Berwick, it was only to a limited extent that he allowed himself to take part in public work outside that which came to him as a minister and Professor of Theology.  There were, however, two public questions which interested him deeply, and the solution of which he did what he could by speech and influence to further.  One of these was the question of Temperance.  During the first twenty years of his ministry he had not felt called upon to take up any strong position on this question, although personally he had always been one of the most abstemious of men.  But about the year 1864 he had, without taking any pledge or enrolling himself on the books of any society, given up the use of alcohol.  He had done so largely as an experiment—­to see whether his influence would thereby be strengthened with those in his own congregation and beyond it whom he wished to reclaim from intemperance.

When he became a professor he was invited to succeed Dr. Lindsay as President of the Students’ Total Abstinence Society, and, as no absolute pledge was exacted from the members, he willingly agreed to do so.  From this time his influence was more and more definitely enlisted on behalf of Total Abstinence, and in 1874 he took a further step.  In trying to save from intemperance a friend in Berwick who was not a member of his own congregation, he urged him to join the Good Templars, at that time the only available society of total abstainers in the town.  In order to strengthen his friend’s hands, he agreed to join along with him.  This step happily proved to be successful as regarded its original purpose, and Dr. Cairns remained a Good Templar during the rest of his life.