“By that it is meant that these divisions have a certain resemblance to the degrees or steps of a flight of stairs, or the rounds of a ladder. The red liquid goes up or down from division to division just as we mount or descend a flight of stairs step by step. If it grows warmer, the red liquid moves and little by little climbs the steps; if colder, it goes down the ladder. Thus the heat can be estimated according to the step or degree where the liquid stops.
“It is freezing when the liquid goes down to zero; the heat is that of boiling water when it goes up to division 100. The intermediate steps or degrees indicate, evidently, other states of heat, greater when the degree is higher up on the ladder.
“The degree of heat of any body, as indicated by the thermometer, is called its temperature. Thus we say the temperature of freezing water is zero, that of boiling water one hundred degrees.”
[3]. It is the centigrade thermometer that is here described.—Translator.
“One morning,” said Emile, “when you sent me to get something from your room, I put my hand on the little bulb of the thermometer. The red liquid began to go up, little by little.”
“It was the warmth of your hand that made it go up.”
“I wanted to see how high the liquid would go, but I had not patience to wait till the end.”
“I will tell you. At last the thermometer would have marked at most 38 degrees, which is the temperature of the human body.”
“And in the very hot days of summer what degree does the thermometer mark?” asked Jules.
“In our region the greatest heat of summer is from 25 to 35 degrees.”