Natural Philosophy for Schools, Families, and Private Students (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1848 Excerpt: ...Effect of Heat upon Air. 430. Heat, which so much affects solids and liquids, has a powerful influence upon air. Of this we are continually reminded by the changes of temperature around us; thus we say, the air 427. What is indicated by the rising of the barometer? Fall of the barometer at the time of the Lisbon earthquake. 428. Mean pressure of the atmosphere at the level of the sea. 429. Use of connecting the thermometer with the barometer. Effect of temperature upon the barometer. 430. Causes of variations in the temperature of the air. Effect of heat upon air is chilly, warm, cold, &c. But as the moisture or dryness, the stillness or motion of the air, all conduce to these variations of temperature, we are not to attribute them to heat, only. Heat expands air, and thus rarefies, or makes it lighter. Let a bladder, tied at the neck, and containing a small quantity of air, be held near the fire, the sides will soon begin to be pressed out by the expansion, of the air within. On removing the bladder to a colder place, the air will condense, and its sides collapse as before. 431. The balloons first used were filled with hot air, which, being lighter than the atmosphere around, arose, and floated in it. Dr. Arnott says, "the first balloon was constructed by a man ignorant of what he was really effecting. Seeing the clouds float high in the atmosphere, he thought that if he could make a cloud, and inclose it in a bag, it might rise and carry him with it. Then erroneously deeming smoke and a cloud the same substance, he made a fire of green wood, wool, &c., and placed a great bag over it, with the mouth downwards to receive the smoke. He soon had the joy to see the bag full, and ascending; but he understood not that the cause was the hot and dilat...