I fully believe there is not one in ten--no, not one in a hundred--of the most intelligent men in that entire street, doctor, lawyer, architect, or any other, that can give you an accurate account of the condition of the air breathed during any one hour of the day. That is not all. There is scarcely one in a hundred that can satisfy you, by an intelligent description, of the means used for providing it: First--Assuming the air outside to be pure, that there was a constant, positive and sufficient supply of that outside air introduced. Secondly--That that pure air was not deteriorated by overheating, or contaminated by being mixed with the poisonous gases of the burning coal. Thirdly--That there was sufficient moisture added to it to compensate for its increased capacity for moisture, due to its expansion by the additional heat given to it, (which is a very important thing.) Fourthly--That there was any accurate, positive means provided for insuring the fresh air to be brought within reach of the lungs of those for whom it was intended. And, lastly--That there was a positive means provided for the removal of all the poisoned air thrown from the lungs, so that none could possibly be _re-breathed_. No; you will find them in close, unventilated offices, in close factories, in almost _air-tight_ dwellings. In the large stores they do better. The air is very commonly overheated, it is often mixed with impurities, and very seldom supplied with a proper amount of additional moisture. The air is often so dry, that in a few minutes' conversation the linings of the air-passages to your lungs become parched and husky, producing irritation and a feverish condition of the system. And even in this room, to-night, do you see any opening at your feet, connected with a heated flue, for drawing the foul air from the floor as fast as thrown from your lungs? I believe there is not a square inch provided for that purpose. Or, do you see any escape immediately above the gas-lights, for carrying off the burned air while hot enough to escape? Not one. There are two or three openings, I think, in the back part of the room, just at the ceiling, but for your breath to get there, it must rise and pass by the zone of respiration, and much of it be again re-breathed; and the products of combustion, as we have seen, would cool sufficiently to fall to the floor long before they reached that point. I take the liberty of calling your attention to this with more freedom, because it does not indicate any special inattention on the part of the Managers. It is not an exceptional case, but it is the rule. It is the popular opinion of the proper means of ventilation.