ANCIENT POTTERS AT WORK.
The Doctor explained that the modes of making these bottles had changed very little in five thousand years, as they could see by the pictures on the walls of the tombs. The ancient Egyptians were familiar with the wheel and its uses; the potter of the time of Rameses II. manipulated the clay in the same manner as his descendant of to-day, and he doubtless knew the necessary proportions of clay and sifted ashes for making his composition.
ANCIENT VASES, CUPS, AND WATER-JARS.
The boys had already observed the porous character of the Egyptian water-bottle. It allows the water to pass through so freely that the outside is constantly wet; in the dry air of Egypt this outside water evaporates rapidly, and every student of natural philosophy knows that evaporation produces coolness. Especially is this the case if the bottle is placed where there is a current of air, as the evaporation is greatly increased by the action of the wind. One day the boys made an experiment with one of these bottles with the following result:
The temperature of the air was 81° Fahrenheit, and so was that of the water with which the bottle was filled. It was hung in a shady place, where there was a good draught, and in half an hour a thermometer lowered into the bottle showed that the water had fallen to 63°, or eighteen less than the surrounding temperature.
This process, or a similar one, is in use in all hot countries. Doctor Bronson told the youths that he had seen bottles very like the Egyptian ones in Mexico and South America. In some cases, where the material was not porous, the coolness was produced by wrapping a piece of cloth around a bottle, and keeping it constantly wet while hanging in a current of air.