Q. How do you know that air is condensed by cold?
A. After the bladder is fully inflated, (by lying before the fire), if it be taken away from the fire, the bladder will collapse, and show that it is not half full.
Q. What is meant by the bladder “collapsing?”
A. The skin will become wrinkled, shrivelled, and flabby, because there is not sufficient air inside to fill it out.
Q. How do you know that condensed air will descend?
A. As soon as the cotton of the balloon is burnt out, the air inside becomes cold again, and the balloon falls to the earth.
Q. Does the sun heat the air as it does the earth?
A. No; the air is not heated by the rays of the sun, because air (like water) is a very bad conductor.
Q. How is the air heated?