A temperature very near to that of the total absence of that molecular movement or vibration which we call "heat," can now be attained by the use of liquid hydrogen, which enables us, by its evaporation, to come within a few degrees (actually three!) of that condition known as the "absolute zero." We divide into one hundred equal steps or degrees the column of liquid (mercury, spirit, or other liquid) of a thermometer as it expands from the shrunken bulk which it occupies when placed in freezing water to the full length which it attains when the water is heated to boiling point. This is called the centigrade scale, or scale of a hundred degrees. But, as we know by the records of travellers in the Arctic regions and by the experiments made in laboratories, there are "degrees" of coldness or diminution of heat which are much below that of freezing water, and can be measured by the further shrinking of the column of liquid in the thermometer, so that we record "degrees below zero centigrade," each of the same length as those above it and corresponding to the same "quantum" of decrease or increment of heat. As we pass from the temperature at which water is solid to that much lower or diminished state of hotness at which mercury becomes solid, the shrinking column of the thermometer (in which a liquid is used not rendered solid by this amount of cooling) falls through 39 degrees of the centigrade size, so that we say that mercury freezes at minus 39 or at 39 degrees below zero of the centigrade scale. The conclusion has now been reached that the absolute zero or cessation of all heat in a body is represented by a fall of no less than 273 degrees below zero on the centigrade scale. Hydrogen gas becomes a liquid at 252 degrees below zero centigrade, and a solid at 264 degrees. If we start our counting of those degrees or increments of heat, of which there are 100 between the freezing and boiling points of water, at the absolute zero or condition of total absence of heat, we must say that hydrogen "melts"–that is, passes from the solid to the liquid state–at 11 degrees (absolute), and boils at about 20 degrees (absolute), whilst water does not melt until 273 degrees (absolute) of temperature are reached, and boils at 373 degrees above the absolute zero.