No sooner was this book off his hands than Cairns was urged to undertake another biographical work—­the Life of George Wilson.  But this, in view of his recent experience, he steadfastly refused to do, and contented himself with writing a sketch of his friend for the pages of Macmillan’s Magazine.  When, however, Wilson’s biography was taken in hand by his sister, Cairns promised to help her in every possible way with his advice and guidance, and this he did from week to week till the book was published.  This help on his part was continued by his seeing through the press Wilson’s posthumous book, Counsels of an Invalid, which appeared in 1862.  With the completion of this task he seemed to be free to return to his theological work, and he did return to it; but his release turned out to be only a brief respite.  In 1863 the ten years’ negotiations for Union between the Free and United Presbyterian Churches, in which he felt impelled to take a prominent and laborious part, were begun, and they absorbed nearly all of his leisure during what might have been a productive period of his life.  When he emerged from them he was fifty-four years of age, he had passed beyond the time of life when his creative powers were at their freshest, and the general habits of his life and lines of his activity had become settled and stereotyped.

This is not the place in which to enter into a detailed account of the Union negotiations.  That has been done with admirable lucidity and skill by such writers as Dr. Norman Walker in his Life of Dr. Robert Buchanan, and by Dr. MacEwen in his Life of the subject of the present sketch, and it does not need to be done over again.  But something must be said at this point to indicate the general lines which the negotiations followed and to make Cairns’s relation to them clear.  That he should have taken a keen and sympathetic interest in any great movement for ecclesiastical union was quite what might have been expected.  What interested him in Christian truth, and what he had, ever since he had been a student, set himself specially to expound and defend, were the great catholic doctrines which are the heritage of the one Church of Christ.  Constitutionally, he was disposed to make more of the things that unite Christians than of those which divide them; and, while he was loyally attached to his own Church, many of his favourite heroes, as well as many of his warmest personal friends, belonged to other Churches.  Hence anything that made for Union was entirely in line with his feelings and his convictions.  Thus he had thrown himself heartily into the work of the Evangelical Alliance, and at its memorable Berlin Meeting of 1857 had created a deep impression by an address which he delivered in German on the probable results of a closer co-operation between German and British Protestantism.  In the same year he took part in a Conference in Edinburgh which had been summoned by Sir George Sinclair of Ulbster to discuss the possibility of Church Union at home.  And when in 1859 the Union took place in the Australian Colonies of the Presbyterian Churches which bore the names of the Scottish Churches from which they had sprung, it was to a large extent through his influence that the Australian United Presbyterians took part in the Union.