"The decorum of the visitors has been excellent, and it is remarkable, in view of such a very large number of persons visiting the room, that so few mutilations and injuries occur to the periodicals and books, and that so few books, probably not more than half a dozen in the course of a year, and those of small consequence, are stolen." It seems then, after all, that Peter Cooper's faith in the people was justified. The great hall in the basement is another noteworthy feature, and worthy of wider imitation than it has yet received. Such a hall, if located upstairs in such a building, would have been open to three objections: it would have monopolized, for occasional use only, space which was required for constant use; it would have been intolerably noisy, by reason of the roar and rattle in the streets which surround the building on all sides; and it would have been dangerous, as all such places are, when great audiences must make their exit by going down stairs. Nothing has ever been invented that will prevent people from being crushed and trampled when they are crowding down a stairway. In all these respects, the great hall of the Cooper Union is admirable. It occupies space not otherwise valuable. It is quiet, and acoustically perfect. The means of exit and entrance are ample and safe. Even in case of an unreasoning panic, there is little danger that a crowd, tumbling up the stone stairways to the street, would cause the horrible maiming and killing which so often attend the efforts of a frightened multitude to get down. Finally, the ventilation is excellent, for the simple reason that natural or automatic ventilation of such a large, low basement room could not be expected, and consequently mechanical ventilation by means of a large fan, run by steam power, was provided. The efficiency of this system has sometimes been severely tested. On one occasion, during a scientific lecture, the experimental illustrations of which were on a large and imposing scale, the learned professor on the platform had the misfortune to crack an immense glass jar, in which he was exhibiting the brilliant combustion of phosphorus in oxygen gas. The white fumes of phosphorous acid floated out into the air, and began to diffuse themselves through the hall towards the ventilation outlets at the sides and rear. To one who knew the irritating nature of these fumes it seemed inevitable that the hall must be emptied of its crowded audience in a few minutes. Already coughing had begun on the front seats, when Mr. Hewitt, who was seated on the platform, quickly rose, and pulling a cord, reversed the currents of ventilation and opened a new outlet into the street, behind and above the platform. The curling clouds of vapor paused, wheeled, and retreated, and in another minute the air was perfectly pure. The lecturer had not even been interrupted. It was a beautiful and timely "experiment" not on the programme, and, to use the