But the significance of the Congress of Arts and Science ought not to be measured and valued only by reference to this printed result. Its less visible side-effects seem in no way less important for scholarship, and they are fourfold. There was, first, the personal contact between the scholarly public and the leaders of thought; there was, secondly, the first academic alliance between the United States and Europe; there was, thirdly, the first demonstration of a world congress crystallized about one problem; there was, fourthly, the unique accentuation of the thought of unity in all human science; and each of these four movements will be continued and reinforced by the publication of these proceedings. The first of these four features, the contact of the scholarly public with the best thinkers of our time, had, to be sure, its limitations. It was not sought to create a really popular congress. Neither the level of the addresses, nor the size of the halls, nor the number of invitations sent out, nor the general conditions of a world's fair at which the expense of living is high and the distractions thousandfold, favored the attendance of crowds. It was planned from the first that on the whole scholars and specialists should attend and that the army should be made up essentially of officers. If in an astronomical section perhaps thirty men were present, among whom practically every one was among the best known directors of observatories or professors of mathematics, astronomy, or physics, from all countries of the globe, much more was gained than if three thousand had been in the audience, brought together by an interest of curiosity in moon and stars. For the most part there must have been between a hundred and two hundred in each of the 128 sectional meetings, and that was more than the organizers expected. This direct influence on the interested public is now to be expanded a thousandfold by the mission work of these volumes. The concentration of these hundreds of addresses into a few days made it in any case impossible to listen to more than to a small fraction; these volumes will bring at last all speakers to coördinated effectiveness; and while one hall suffered from bad acoustics, another from bad ventilation, and a third from the passing of the intermural trains, here at least is an audience in which nothing will disturb the sensitive nerves of the willing follower.