All fluids except water diminish in bulk till they freeze. Thus, fill a large thermometer tube with water, say of the temperature of eighty degrees, and then plunge the bulb into pounded ice and salt, or any other freezing mixture; the water will go on shrinking in the tube till it has attained the temperature of about forty degrees, and then, instead of continuing to contract till it freezes, it will be seen slowly to expand, and consequently to rise in the tube until it congeals.

In this case the expansion below forty degrees and above forty degrees seem to be equal, so that the water will be of the same bulk at thirty-two degrees as at forty-eight degrees, that is, at eight degrees above or below forty degrees.