| | DEGREES | | | | 10000 --+ +-- Conjectural heat | | of the sun. | | | | | | | | 7000 --+ +-- Highest heat | | yet obtained | | artificially. | | | | | | | | 3500 --+ +-- Steel boils. | | | | | | | | | | 212 --+ +-- Water boils. 0 --+=+-- Zero. 461 --+=+-- Prof. Dewar's |=| absolute zero. {===} | DEGREES | | 0 --+-- Zero. | 40 --+-- Mercury freezes. | | | | | | | 202 --+-- Alcohol freezes. | | | | 300 --+-- Oxygen boils. 312 --+-- Liquid air boils. 320 --+-- Nitrogen boils. | | | | | 440 --+-- Hydrogen boils. 461 --+-- Prof. Dewar's absolute zero.] Think what this absolute zero means. Heat, we know, like electricity and light, is a vibratory or wave motion in the ether. The greater the heat, the faster the vibrations. We think of all the substances around us as solids, liquids, and gases, but these are only comparative terms. A change of temperature changes the solid into the liquid, or the gas into the solid. Take water, for instance. In the ordinary temperature of summer it is a liquid, in winter it is a hard crystalline substance called ice; apply the heat of a stove and it becomes steam, a gas. So with all other substances. Air to us is an invisible gas, but if the earth should suddenly drop in temperature to 312° below zero all the air would fall in liquid drops like rain and fill the valleys of the earth with lakes and oceans. Still a little colder and these lakes and oceans would freeze into solids. Similarly, steel seems to us a very hard and solid substance, but apply enough heat and it boils like water, and finally, if the heat be increased, it becomes a gas. Imagine, if you can, a condition in which all substances are solids; where the vibrations known as heat have been stilled to silence; where nothing lives or moves; where, indeed, there is an awful nothingness; and you can form an idea of the region of the coldest cold--in other words, the region where heat does not exist. Our frozen moon gives something of an idea of this condition, though probably, cold and barren as it is, the moon is still a good many degrees in temperature above the absolute zero.