At the point of freezing, the thermometer if placed on the ice will register 32 degrees. If the ice is allowed to melt, the water at the moment of liquefaction would be found to register the same degree of temperature as the ice when first frozen. And yet there has been a vast expenditure of energy between the points of liquefaction and congelation, notwithstanding the temperature of ice may be lowered, after it is formed, many degrees, which is measurable by the thermometer. Suppose we take a piece of ice which is 10 degrees below the freezing point and insert in it a thermometer. If now we apply heat to this ice the thermometer will gradually rise until it reaches the melting point at 32 degrees Fahrenheit, where it will stand until all the ice is melted. The application of heat is going on steadily, but there are no indications of movement in the mercury until the last trace of ice with which it is in contact has been liquefied. After the ice is all melted, if the application of heat to the body of liquefied ice be continued, the column of mercury will resume its movement upward until it reaches the boiling point, where it is again arrested. And no matter how much heat is applied to the boiling water, if in an open vessel, the thermometer remains the same until all the water is evaporated. Here are two curious facts, and they are facts that, if we can master them, will serve as a key to the understanding of much that is mysterious in nature. It will be our endeavor to give the reader a mental picture of what is taking place during the time the ice is melting and the thermometer is stationary. Do not suppose that you can understand this, even so far as it is understandable, by a casual reading without thought. No man was ever yet able to present a picture to the mind of another, however clearly and simply it may be done, unless that other mind is receptive. When a photographer trains his camera upon an object, however intense the light may be and however clean-cut the picture that is thrown upon the plate in the camera, unless that plate is properly sensitized so that the picture may be impressed upon it, all of the other conditions are in vain. The reader is always a part of the book he is reading. CHAPTER XXIII. STORED ENERGY IN WATER.