It had all along been felt that Dr. Cairns must sooner or later find scope for his special powers and acquirements in a professor's chair. In the early years of his ministry he received no fewer than four offers of philosophical professorships, which his views of the ministry and of his consecration to it constrained him to set aside. Three similar offers of theological chairs, the acceptance of which did not involve the same interference with the plan of his life, came to him later, but were declined on other grounds. When, however, a vacancy in the Theological Hall of his own Church occurred by the death of Professor Lindsay, in 1866, the universal opinion in the Church was that it must be filled by him and by nobody else. Dr. Lindsay had been Professor of Exegesis, but the United Presbyterian Synod in May 1867 provided for this subject being dealt with otherwise, and instituted a new chair of Apologetics with a special view to Dr. Cairns's recognised field of study. To this chair the Synod summoned him by acclamation, and, having accepted its call, he began his new work in the following August.

As in his own student days, the Hall met for only two months in each year, and the professors therefore did not need to give up their ministerial charges. So he remained in Berwick, where his congregation were very proud of the new honour that had come to their minister, and that was in some degree reflected on them. Instead of "the Doctor" they now spoke of him habitually as "the Professor," and presented him with a finely befrogged but somewhat irrelevant professor's gown for use in the pulpit at Wallace Green.

Dr. Cairns prepared two courses of lectures for his students—one on the History of Apologetics, and the other on Apologetics proper, or Christian Evidences. For the former, his desire to go to the sources and to take nothing at second-hand led him to make a renewed and laborious study of the Fathers, who were already, to a far greater extent than with most theologians, his familiar friends. His knowledge of later controversies, such as that with the Deists, which afterwards bore fruit in his work on "Unbelief in the Eighteenth Century," was also widened and deepened at this time. These historical lectures were almost overweighted by the learning which he thus accumulated; but they were at once massive in their structure and orderly and lucid in their arrangement.

In the other course, on Christian Evidences, he did not include any discussion on Theism which—probably because of his special familiarity with the Deistical and kindred controversies, and also because the modern assaults on supernatural Christianity from the Evolutionary and Agnostic standpoint had not yet become pressing—he postulated. And, discarding the traditional division of the Evidences into Internal and External, he classified them according to their relation to the different Attributes of God, as manifesting His Power, Knowledge, Wisdom, Holiness, and Benignity. With this course he incorporated large parts of his unfinished treatise on "The Difficulties of Christianity," which, after he had thus broken it up, passed finally out of sight.

The impression which he produced on his students by these lectures, and still more by his personality, was very great. "I suppose," writes one of them, "no men are so hypercritical as students after they have been four or five years at the University. To those who are aware of this, it will give the most accurate impression of our feeling towards Dr. Cairns when I say that, with regard to him, criticism could not be said to exist. We all had for him an appreciation which was far deeper than ordinary admiration; it was admiration blended with loyalty and veneration."16 Specially impressive were the humility which went along with his gifts and learning, and the wide charity which made him see good in everything. One student's appreciation of this latter quality found whimsical expression in a cartoon which was delightedly passed from hand to hand in the class, and which represented Dr. Cairns cordially shaking hands with the Devil. A "balloon" issuing from his mouth enclosed some such legend as this: "I hope you are very well, sir. I am delighted to make your acquaintance, and to find that you are not nearly so black as you are painted."

During the ten years' negotiations for Union a considerable number of pressing reforms in the United Presbyterian Church were kept back from fear of hampering the negotiations, and because it was felt that such matters might well be postponed to be dealt with in a United Church. But, when the negotiations were broken off, the United Presbyterians, having recovered their liberty of action, at once began to set their house in order. One of the first matters thus taken up was the question of Theological Education. As has been already mentioned, the theological curriculum extended over five sessions of two months. It was now proposed to substitute for this a curriculum extending over three sessions of five months, as being more in accordance with the requirements of the times and as bringing the Hall into line with the Universities and the Free Church Colleges. A scheme, of which this was the leading feature, was finally adopted by the Synod in May 1875. It necessarily involved the separation of the professors from their charges, and accordingly the Synod addressed a call to Dr. Cairns to leave Berwick and become Professor of Systematic Theology and Apologetics in the newly constituted Hall, or, as it was henceforth to be designated—"College." In this chair it was proposed that he should have as his colleague the venerable Dr. Harper, who was the senior professor in the old Hall, and who was now appointed the first Principal of the new College.

Dr. Cairns had thus to make his choice between his congregation and his professorship, and, with many natural regrets, he decided in favour of the latter. This decision, which he announced to his people towards the close of the summer, had the incidental effect of keeping him in the United Presbyterian Church, for in the following year the English congregations of that Church were severed from the parent body to form part of the new Presbyterian Church of England; and Wallace Green congregation, somewhat against its will, and largely in response to Dr. Cairns's wishes, went with the rest. He had still a year to spend in Berwick, broken only by the last session of the old Hall in August and September, and that year he spent in quiet, steady, and happy work. In June 1876 he preached his farewell sermon to an immense and deeply moved congregation from the words (Rom. i. 16), "I am not ashamed of the gospel of Christ: for it is the power of God unto salvation unto every one that believeth." "For more than thirty years," he concluded, "I have preached this gospel among you, and I bless His name this day that to not a few it has by His grace proved the power of God unto salvation. To Him I ascribe all the praise; and I would rather on such an occasion remember defects and shortcomings than dwell even upon what He has wrought for us. The sadness of parting from people to whom I have been bound by such close and tender ties, from whom I have received every mark of respect, affection, and encouragement, and in regard to whom I feel moved to say, 'If I forget thee, O Jerusalem, let my right hand forget her cunning,' inclines me rather to self-examination and to serious fear lest any among you should have suffered through my failure to set forth and urge home this gospel of salvation. If then any of you should be in this case, through my fault or your own, that you have not yet obeyed the gospel of Christ, I address to you in Christ's name one parting call that you may at length receive the truth."

A few weeks later he and his sister removed to Edinburgh, where they were joined in the autumn by their brother William. William Cairns, who had been schoolmaster at Oldcambus for thirty-two years, was in many respects a notable man. Deprived, as we have seen, in early manhood of the power of walking, he had set himself to improve his mind and had acquired a great store of general information. He was shrewd, humorous, genial, and intensely human, and had made himself the centre of a large circle of friends, many of whom were to be found far beyond the bounds of his native parish and county. Since his mother's death an elder sister had kept house for him, but she had died in the previous winter, and at his brother's urgent request he had consented to give up his school al Oldcambus and make his home for the future with him in Edinburgh. The house No. 10 Spence Street, in which for sixteen years the brothers and sister lived together, is a modest semi-detached villa in a short street running off the Dalkeith Road, in one of the southern suburbs of the city. It had two great advantages in Dr. Cairns's eyes—one being that it was far enough away from the College to ensure that he would have a good walk every day in going there and back; and the other, that its internal arrangements were very convenient for his brother finding his way in his wheel-chair about it, and out of it when he so desired.

The study, as at Berwick, was upstairs, and was a large lightsome room, from which a view of the Craigmillar woods, North Berwick Law, and even the distant Lammermoors, could be obtained—a view which was, alas! soon blocked up by the erection of tall buildings. At the back of the house, downstairs, was the sitting-room, where the family meals were taken and where William sat working at his desk. He had been fortunate enough to secure, almost immediately after his arrival in Edinburgh, a commission from Messrs. A. & C. Black to prepare the Index to the ninth edition of the Encyclopaedia Britannica, then in course of publication. During the twelve years that the work lasted he performed the possibly unique feat of reading through the whole of the twenty-five volumes of the Encyclopaedia, and thus added considerably to his already encyclopaedic stock of miscellaneous information. Opening off the sitting-room was a smaller room, or rather a large closet, commanding one of the finest views in Edinburgh of the lion-shaped Arthur's Seat; and here of an evening he would sit in his chair alone, or surrounded by the friends who soon began to gather about him,

Sometimes a more than usually resounding peal of laughter would bring the professor down from his study to find out what was the matter, and to join in the merriment; and then, after a few hearty words of greeting to the visitors, he would plead the pressure of his work and return to the company of Justin or Evagrius.

His three nephews, who during the Edinburgh period were staying in town studying for the ministry, always spent Saturday afternoon at Spence Street, and sometimes a student friend would come with them. Dr. Cairns was usually free on such occasions to devote an hour or two to his young friends. He was always ready to enter into discussions on philosophical problems that happened to be interesting them, and the power and ease with which he dealt with these gave an impression as of one heaving up and pitching about huge masses of rock. His part in these discussions commonly in the end became a monologue, which he delivered lying back in his chair, with his shoulders resting on the top bar of it, and which he sometimes accompanied with the peculiar jerk of his right arm habitual to him in preaching. A snell remark of his brother William suggesting some new and comic association with a philosophic term dropped in the course of the discussion, would bring him back with a roar of laughter to the actual world and to more sublunary themes. When the young men rose to leave he always accompanied them to the front door, and bade each of them good-bye with a hearty "ΠÁντα τÀ καλÁ σοι γÉνοιτο," 17 [Greek: Panta ta kala soi genoito] and an invariable injunction to "put your foot on it,"—"it" being the spring catch by which the gate was opened.

Once a week during the session a party of six or eight students came to tea at Spence Street, until the whole of his two classes had been gone over. After tea in the otherwise seldom used dining-room of the house, some of the party accompanied the professor to the study. Here he would show them his more treasured volumes, such as his first edition of Butler, which he would tell them he made a point of reading through once a year. Others, who preferred a less unclouded atmosphere, withdrew with his brother into his sanctum. Soon all reassembled in the dining-room, and a number of hymns were sung—some of Sankey's, which were then in everybody's mouth, some of his favourite German hymns with their chorals, which might suggest references to his student days in Berlin or to later experiences in the Fatherland, and some by the great English hymn-writers. At last came family worship, always impressive as conducted by him, but often the most memorable feature by far in these gatherings. It was a very simple, and may seem a very humdrum, way of spending an evening; but the homely hospitality of the household—the conversational gifts, very different in kind as these were, of himself and his brother—and, above all, his genial and benignant presence, made everything go off well, and the students went away with a deepened veneration for their professor now that they had seen him in his own house.

During his first two years in Edinburgh he was busily engaged in writing lectures and in adapting his existing stock to the requirements of the new curriculum. Of these lectures, and of others which he wrote in later years, it must be said that, while all of them were the fruit of conscientious and strenuous toil, they were of unequal merit, or at least of unequal effectiveness. Some of them, particularly in his Apologetic courses, were brilliant and stimulating. Whenever he had a great personality to deal with, such as Origen, Grotius, or Pascal, or, in a quite different way, Voltaire, he rose to the full height of his powers. His criticisms of Hume, of Strauss, and of Renan, were also in their own way masterly. But a course which he had on Biblical Theology seemed to be hampered by a too rigid view of Inspiration, which did not allow him to lay sufficient stress on the different types of doctrine corresponding to the different individualities of the writers. And when, after the death of Principal Harper, he took over the entire department of Systematic Theology, his lectures on this, the "Queen of sciences," while full of learning and sometimes rising to grandeur, gave one on the whole a sense of incompleteness, even of fragmentariness. This impression was deepened by the oral examinations which he was in the habit of holding every week on his lectures.

For these examinations he prepared most carefully, sitting up sometimes till two o'clock in the morning collecting material and verifying references which he deemed necessary to make them complete. His aim in them was not only to test the students' attention and progress, but to communicate information of a supplementary and miscellaneous character which he had been unable to work into his lectures. And so he would bring down to the class a tattered Father or two, and would regale its members with long Greek quotations and with a mass of details that were pure gold to him but were hid treasure to them. His examination of individual students was lenient in the extreme. It used to be said of him that if he asked a question to which the correct answer was Yes, while the answer he got was No, he would exert his ingenuity to show that in a certain subtle and hitherto unsuspected sense the real answer was No, and that Mr. So-and-so deserved credit for having discovered this, and for having boldly dared to say No at the risk of being misunderstood. This, of course, is caricature; but it nevertheless sufficiently indicates his general attitude to his students.

It was the same with the written as with the oral examinations. In these he assigned full marks to a large proportion of the papers sent in. Once it was represented to him that this method of valuation prevented his examination results from having any influence on the adjudication of a prize that was given every year to the student who had the highest aggregate of marks in all the classes. He admitted the justice of this contention, and promised to make a change. When he announced the results of his next examination it was found that he had been as good as his word; but the change consisted in this: that whereas formerly two-thirds of the class had received full marks, now two-thirds of the class received ninety per cent.!

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.

While there were some things about the Order that did not appeal to him, such as the ritual, the "regalia," and the various grades of membership and of office, with their mysterious initials, he looked upon these things as non-essentials, and was in hearty sympathy with its general principles and work. But, although he was often urged to do so, he never would accept office nor advance beyond the initiatory stage of membership represented by the simple white "bib" of infancy. On coming to Edinburgh, he looked about for a Lodge to connect himself with, and ultimately chose one of the smallest and most obscure in the city. The members consisted chiefly of men and women who had to work so late that the hour of meeting could not be fixed earlier than 9 p.m. He was present at these meetings as often as he could, and only lamented that he could not attend more frequently.

While fully recognising the right of others to come to a different conclusion from his own, and while uniformly basing his total abstinence on the ground of Christian expediency and not on that of absolute Divine law, his view of it as a Christian duty grew clearer every year. And he carried his principles out rigidly wherever he went. He perplexed German waiters by his elaborate explanations as to why he drank no beer; and once, as he came down the Rhine, he had a characteristically sanguine vision of the time when the vineyards on its banks would only be used for the production of raisins. At the same time his interest in Temperance work, alike in its religious, social, and political aspects, was always becoming keener. He was frequently to be found on Temperance platforms, and was in constant request for the preaching of Temperance sermons. Some of his speeches and sermons on the question have been reprinted and widely read, and one New Year's tract which he wrote has had a circulation of one hundred and eighty thousand.

The other question in which he took a special interest was that of Disestablishment. To those who adopted the "short and easy method" of accounting for the Disestablishment movement in Scotland by saying that it was all due to jealousy and spite on the part of its promoters, his adhesion to that movement presented a serious difficulty. For no one could accuse him of jealousy or spite. Hence it was a favourite expedient to represent him as the tool of more designing men—as one whose simplicity had been imposed upon, and who had been thrust forward against his better judgment to do work in which he had no heart. This theory is not only entirely groundless, but entirely unnecessary; because the action which he took on this question can readily be explained by a reference to convictions he had held all his life, and to circumstances which seemed to him to call for their assertion.

He had been a Voluntary ever since he had begun to think on such questions. His father, in the days of his boyhood, had subscribed, along with a neighbour, for the Voluntary Church Magazine, and the subject had often been discussed in the cottage at Dunglass. It will be remembered that during his first session at the University he was an eager disputant with his classmates on the Voluntary side, and that towards the close of his course, after a memorable debate in the Diagnostic Society, he secured a victory for the policy of severing the connection between Church and State. These views he had never abandoned, and in a lecture on Disestablishment delivered in Edinburgh in 1872 he re-stated them. While admitting, as the United Presbyterian Synod had done in adopting the "Articles of Agreement," that the State ought to frame its policy on Christian lines, he denied that it was its duty or within its competence to establish and endow the Church. This is, to quote his own words, "an overstraining of its province,—a forgetfulness that its great work is civil and not spiritual,—and an encroachment without necessity or call, and indeed, as I believe, in the face of direct Divine arrangements, on the work of the Christian Church."

These, then, being his views, what led him to seek to make them operative by taking part in a Disestablishment campaign? Two things especially. One of these was the activity at that time of a Broad Church party within the Established Church. He maintained that this was no mere domestic concern of that Church, and claimed the right as a citizen to deal with it. In a national institution views were held and taught of which he could not approve, and which he considered compromised him as a member of the nation. He felt he must protest, and he protested thus.

The other ground of his action was the conviction, which recent events had very much strengthened, that the continued existence of an Established Church was the great obstacle to Presbyterian Union in Scotland. It is true that there was nothing in the nature of things to prevent the Free and United Presbyterian Churches coming together in presence of an Established Church. As a matter of fact, they have done so since Dr. Cairns's death, though not without secessions, collective and individual. But experience had shown that it was the existence of an Established Church, towards which the Anti-Union party had turned longing eyes, which was the determining factor in the wrecking of the Union negotiations. Besides, Dr. Cairns looked forward to a wider Union than one merely between the Free and United Presbyterian Churches, and he was convinced that only on the basis of Disestablishment could such a Union take place. To the argument that, if the Church of Scotland were to be disestablished, its members would be so embittered against those who had brought this about that they would decline to unite with them, he was content to reply that that might safely be left to the healing power of time. The petulant threat of some, that in the event of Disestablishment they would abandon Presbyterianism, he absolutely declined to notice.

The Disestablishment movement had been begun before Dr. Cairns left Berwick, and he supported it with voice and pen till the close of his life. He did so, it need not be said, without bitterness, endeavouring to make it clear that his quarrel was with the adjective and not with the substantive—with the "Established" and not with the "Church," and under the strong conviction that he was engaged "in a great Christian enterprise."