And we believe no similar amount of money or thought, will produce a greater amount of satisfaction than the increased health, strength and happiness thus secured. LECTURE II. As I stated in our last lecture, much interest is being awakened, in this country and in Europe, by recent investigations showing the enormous numbers of untimely deaths that are caused throughout all classes of society by foul air. It would have been a startling announcement, ten years ago, to have stated that impure air caused as many deaths, and as much sickness, as all other causes combined, and yet the most diligent and accurate investigations are rapidly approaching that conclusion. Few really comprehend the immense pecuniary loss, to say nothing of the amount of suffering, that we endure by this extra and easily preventible amount of sickness. I propose, this evening, to enter upon the consideration of one of the most important parts of our subject--_the effect produced by_ HEAT _upon the movements of air_. I think it probable that many of us do not comprehend the actual reality of the air. We are apt to say of a room that has no carpet and furniture in it, that it has nothing in it, while, if it is full of air, it has a great deal in it. A room between twenty-seven and twenty-eight feet square contains one ton of air--a real ton, just as heavy as a ton of coal. Now, there is not only twenty-seven feet, but more than twenty-seven miles of air piled on top of us. The pressure of the atmosphere at the level of the ocean is about fifteen pounds to the square inch. An ordinary sized man sustains a pressure of about fifteen tons, and were it not that this pressure is equal in all directions, we would be crushed thereby. We must accustom our minds, therefore, to consider air a real substance, and that it is as totally unable to move itself, or to be moved, without _power_, as water or coal. It requires just as much power to move a ton of _air_ from the cellar to the second story, as it does a ton of coal. Heat is the great moving power of air. Those whose attention has not been especially directed to the subject of the amount of power exerted by the sun's rays upon the earth, have little conception of its magnitude. The power of all the horses in the world, added to the power of all the locomotives, and of all the immense steam engines in all the world, express but a small fraction of the power exerted by the sun's rays upon the earth. It is estimated to be sufficient to boil five cubic miles of ice-cold water every minute. His rays are the chosen power of the Creator for moving all matter upon the globe. It is his rays that lie buried in the vast coal fields beneath the earth. His rays cause every spear of grass to grow, rear the mighty oak, form the rose, burst its beautiful buds, and send its perfume through the air.