"Well," said he, still addressing himself to Miss Miette, "this drawing is concerned with physical science, because the peasant, in placing his cloak before the heat of the fire, causes the phenomenon of evaporation to take place. The vapor which escapes from the damp cloth is water, is nothing but water, and will always be water under a different form. It is water modified, and modified for a moment, because this vapor, coming against the cold wall or other cold objects, will condense. That is to say, it will become again liquid water,—water similar to that which it was a moment ago; and that is a physical phenomenon,—for physical science aims to study the modifications which alter the form, the color, the appearance of bodies, but only their temporary modifications, which leave intact all the properties of bodies. Our drawing is concerned with chemistry, because the piece of wood which burns disappears, leaving in its place cinders in the hearth and gases which escape through the chimney. Here there is a complete modification, an absolute change of the piece of wood. Do what you will, you would be unable, by collecting together the cinders and gases, to put together again the log of wood which has been burned; and that is a chemical phenomenon,—for the aim of chemistry is to study the durable and permanent modifications, after which bodies retain none of their original properties. Another example may make more easy this distinction between physical science and chemistry. Suppose that you put into the fire a bar of iron. That bar will expand and become red. Its color, its form, its dimensions will be modified, but it will always remain a bar of iron. That is a physical phenomenon. Instead of this bar of iron, put in the fire a bit of sulphur. It will flame up and burn in disengaging a gas of a peculiar odor, which is called sulphuric acid. This sulphuric-acid gas can be condensed and become a liquid, but it no longer contains the properties of sulphur. It is no longer a piece of sulphur, and can never again become a piece of sulphur. The modification of this body is therefore durable, and therefore permanent. Now, that is a chemical phenomenon."
Monsieur Roger stopped for a moment; then, paying no apparent attention to Paul, who, however, was listening far more attentively than one could imagine he would, he looked at Miette, and said,—
"I don't know, my child, if I have explained myself clearly enough; but you must certainly understand that in their case the artist has represented, whether he wished to or not, the physical phenomenon and the chemical phenomenon."
"Yes, sir," answered Miette, "I have understood quite well."
"Well," said Monsieur Dalize, "since you are so good a teacher, don't you think that you could, during vacation, cause a little chemistry and a little physical science to enter into that little head?" And he pointed to Paul Solange.
The latter, notwithstanding the sentiment of respectful sympathy which he felt for Monsieur Roger, and although he had listened with interest to his explanations, could not prevent a gesture of fear, so pronounced that everybody began to laugh.
Miette, who wished to console her good friend Paul and obtain his pardon for her teasing, came up to him, and said,—
"Come, console yourself, Paul; I will let you take my portrait a dozen times, as you did last year,—although it is very tiresome to pose for a portrait."
