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.