Pennsylvania, New England, Nova Scotia and Newfoundland, to be at the same time covered with clouds, and its air chilled and condensed. The rarefied air, being lighter, must rise, and the denser air next to it will press into its place. That will be followed by the next denser air, that by the next, and so on. So the water in a long sluice or mill race, being stopped by a gate, is at rest like the air in a calm; but as soon as you open the gate at one end to let it out, the water which is next to the gate begins first to move, that which is next to it follows, and so, though the water proceeds forward to the gate, the motion which began there, runs backward, if one may so speak, to the upper end of the race, where the water is last in motion.
That was all. How simple it was!
In a similar way he started valuable theories about the noxious character of the air exhaled from the lungs, and he may be said to have originated the science of ventilation. The manner in which he tested the effect of heat upon different colors was remarkably characteristic of his simple common-sense way of scientific experiment. He describes it himself, thus:
I took a number of little square pieces of broadcloth from a tailor's pattern card, of various colors. There were black, deep blue, lighter blue, green, purple, red, yellow, white and other colors or shades of colors. I laid them all out upon the snow in a bright sunshiny morning. In a few hours the black, being warmed most by the sun, was sunk so low as to be below the stroke of the sun's rays; the dark blue almost as low, the lighter blue not quite so much as the dark, the other colors less as they were lighter; and the white remained on the surface of the snow, not having entered it at all. (What signifies philosophy that does not apply to home use!) May we not learn from hence, that black clothes are not so fit to wear in a hot, sunny climate as white ones?
The thing was indeed so simple that it appears astonishing, not how anybody should have thought of it, but how anybody could have failed to think of it.
