Both the Eskimos and the Plains Indians used open fires in their shelters for warmth but with very different consequences. The Eskimo house was an airtight igloo made of blocks of ice with a small tunnel-like entrance and a small chimney in the center for smoke from the fire. Temperatures inside this structure easily reached 70 to 80 degrees Fahrenheit although outside temperatures frequently dropped well below zero. Often, the igloo was so hot that the loss of body fluid through perspiration would force the Eskimos to drink cup after cup of ice water. The Plains Indians, on the other hand, placed their fire in a tepee made with long poles and animal skins with an entrance cut directly into one wall. In contrast to the Eskimo shelter, the tepee was far from airtight; drafts came in around the door and through gaps between the skins. At night the Indians would crawl under their blankets, cover their heads, and shiver all night—so much that the blankets would shake! The difference between the Eskimo igloo and the Indian tepee was insulation: the igloo’s walls were solid and airtight whereas those of the tepee permitted a great deal of air to enter.
This passage is written mainly to ______.