Some forty years ago, however, the difficulty began again to be felt, this time much more keenly and more widely than before. The spread of commerce, the facility of travel, the ramifications of the postal service, the development of new nationalities and new literatures, have laid upon civilized peoples a sense of burden and restriction which could never have been felt by their forefathers in the previous century. Added to this, a new sense of solidarity had been growing up in the world; the financial and commercial solidarity, by which any disaster or disturbance in one country causes a wave of disaster or disturbance to pass over the whole civilized globe, was being supplemented by a sense of spiritual solidarity. Men began to realize that the tasks of civilization cannot be carried out except by mutual understanding and mutual sympathy among the more civilized nations, that every nation has something to learn from other nations, and that the bonds of international intercourse must thus be drawn closer. This feeling of the need of an international language led in America to several serious attempts to obtain a consensus of opinion among scientific men regarding an international language. Thus in 1888 the Philosophical Society of Philadelphia, the oldest of American learned societies, unanimously resolved, on the initiative of Brinton, to address a letter to learned societies throughout the world, asking for their co-operation in perfecting a language for commercial and learned purposes, based on the Aryan vocabulary and grammar in their simplest forms, and to that end proposing an international congress, the first meeting of which should be held in Paris or London. In the same year Horatio Hale read a paper on the same subject before the American Association for the Advancement of Science. A little later, in 1890, it was again proposed at a meeting of the same Association that, in order to consider the question of the construction and adoption of a symmetrical and scientific language, a congress should be held, delegates being in proportion to the number of persons speaking each language.