When the crowd on the other side of the baseball grounds yells across the field it seems as though we have heard their cheers as soon as they have been given, and so we have for all practical purposes, although in reality half a second has elapsed while the sound has been coming across the field. The time taken by sound in traveling is more apparent when the volume is sufficient to carry it a long distance. The sound of an explosion of a large quantity of dynamite and ammunition in Jersey City was not heard in Philadelphia, ninety miles away, for over seven minutes after it occurred. [Illustration: CLIFF DWELLINGS, WALPI, ARIZONA] [Illustration: _Photo by Brown Bros._ HOMES OF THE LONG-AGO Famous reproduction of the Cliff-dwellers’ Ruins, near Colorado Springs, Col. The cliff-dwellers of early America built their habitations in the canyons of the Colorado and Rio Grande, where the action of the elements had worn away a layer of soft rock, leaving layers of hard rock above and below as roof and floor for the dwelling.] What were the First Apartment Houses in this Country? A great many years ago, long before the white men came to America, there was a race of Indians called “cliff-dwellers,” because they built their dwelling places far up on the sides of steep cliffs. They probably made their homes so hard to reach in order that they might be safe from visits of their enemies. While many of their homes were small single-family houses, there were also a number of large two and three-story dwellings with many rooms in which different families lived. Some of these cliff dwellings may still be seen in the valleys of the Rio Grande and the Rio Colorado and its tributaries. Close examination shows that many of them were very skilfully built, every advantage being taken of the natural rock formations, and the stones being dressed and laid in clay mortar, very much as the bricklayer does his work on an up-to-date apartment house today. The outsides of the buildings somewhat resembled the cement houses which have been put up in later days, a coat of clay being spread on the outside walls and carefully smoothed off. Oftentimes the inner walls were plastered too. Many relics of the inhabitants have been found in these cliff dwellings, although we cannot tell how they lived, for the region is now rainless and therefore destitute of food plants. Conditions must have been different then and the ground less barren. Why do We Call 32° Above Zero “Freezing”? We know that freezing is the transformation of a liquid into solid under the influence of cold. Each liquid always solidifies at some fixed temperature, which is called its freezing point, and the solid melts again at the same temperature. Thus the freezing point and the melting point, or point of fusion, are the same, and the point is always the same for the same substance.