"Why does this plate get so hot when we pull the wire through?"

"Why do you make a fire by rubbing together two substances?" replied the Professor.

"On account of the friction."

"For that same reason you are making the heat in drawing the copper through the die."

"But I notice that if I hammer a piece of cold iron it will get hot.

There is not any rubbing motion there to make friction."

"Do you think not? You have by that means made the most intense friction. The iron is composed of tiny particles, called atoms, and molecules. When you strike a piece of iron you force these particles in among themselves, and the friction caused by this movement produces the heat."

"Is that true of all substances?"

"Yes."

"Well, if air is forced together will it heat in the same way?"

"Yes, and for the same reason. The tiny particles, of which air is composed, move among each other with such rapidity, under compression, that the heat their frictional contact develops is dependent on the pressure exerted."

"You used the terms 'atom' and 'molecules' a moment ago. What is the difference between them?"

"A molecule is always composed of two or more atoms. An atom is smaller than a molecule, for this reason. Furthermore, an atom comprises only one substance. A molecule has two or more substances in its make-up. For instance, water is composed of two parts of hydrogen and one part of oxygen. One molecule of water, therefore, has three atoms, two of the atoms being hydrogen, and one atom oxygen."

"Baby," the infant orang-outan, had now grown to be a pretty good-sized boy. He would sit at the table and gravely eat with a knife and fork, which he had learned to handle most intelligently. In the various trips which had been made from time to time, the Baby was kept at home, but on more than one occasion he would follow up the wagon, and would as often be welcomed when he did come.

Harry found a good use for him later on, and from that time forward Baby knew that a jaunt into the forest meant a trip for him as well. When it came to tree climbing Baby was in his glory. He would swing from branch to branch, and shake the nuts, and the amusing thing was to see him help gather and throw the nuts into the wagon, in the most business-like fashion. He was never known to laugh, but they had many occurrences which, no doubt, made him smile in his own way.

George was an adept cook. He was fond of making surprising delicacies, and boy-like, they were always the kind that had honey of some sort in their composition. Without any knowledge of cooking, but knowing, in a general way, that eggs and milk were the princ.i.p.al things used in puddings, it was not long before he was regarded as the chef. Baby was sure to be present whenever George occupied the kitchen. And help! Why certainly! He knew what flour meant, and particularly honey. The truth is, that he knew what that meant if George merely looked in the direction of the honey pot.

And talking about eggs! Harry found out about this accomplishment in Baby. In the tall gra.s.s beyond the barley fields were flocks of prairie chickens, and during one of the hunting expeditions he found several nests of eggs. They are just as much more delicious than the common egg as the prairie chicken is more delicate than the hen. Baby never thereafter forgot the eggs. Singularly, he never ate any of them.

Apparently the orang does not crave them in his native state, but the little rascal had an eye to the good things, and when he saw the eggs go into the pudding and cake, there were no scruples on his part.

George had been planning a surprise for the Professor. In many devious ways he learned his age, and August was the month, so in concert with Harry, planned to treat the Professor with a birthday party, the first real attempt at jollification which had been proposed since they landed.

"I remember, he said he would be sixty-five years old on the tenth of August."

"But the trouble is, we don't know when we get to the 10th of the month."

"The chances are he doesn't know, either. But what difference does a day or two make, anyway?"

Among the delicacies which George had prepared were 65 little sweet cakes, because they couldn't put that many candles on the big cake, and the boys knew, from experience, that they would have to use candles, or something else to typify the age.

The "tenth of August" came, and the Professor, in all innocence, proposed a day for hunting. Both boys opposed this, to his surprise. The Professor did not press the matter. As usual, when at home, he was shut up in what they called the laboratory. Even though he should be present in the kitchen he would not be likely to take notice of any extra preparations.

In the meantime Harry had made a bell out of a flat sheet of steel. It was really a gong. When the noon hour arrived and the table had been set ready for the symbolic cake pyramid of little cakes, George ordered the gong to sound, and Harry made such a frightful din with the unexpected noise, that Baby was terribly frightened, and scampered to the loft, his usual place of retreat when reproved or unduly excited.

The Professor was out of the laboratory like a shot, and hurried over to the house. At the same time George returned. "Who has taken my cakes?"

he cried. "There are less than a dozen left." Baby chattered in the loft. The Professor could not understand the commotion. All he knew was that Baby was swinging along the rafters and that George was flying around the kitchen hunting cakes.

"h.e.l.lo, and what is all this? Expecting company?"

"Yes; this is a birthday party."

[Ill.u.s.tration: _"'What is this, a party?' said the professor. 'Yes, a birthday party,' said Harry"_]

"That is a good idea. I suppose you have invited all your friends?"

"Yes; we have invited all we know; just one."

The Professor did not need to be told any more than this. His eyes filled with tears, the first real thing that the boys ever saw on his part that strongly affected them, and when the Professor, his heart so full that he could not speak, silently looked at them, they forgot the feast, and the cakes, and Baby. They thought of home and of what they were doing there, and whether the time would ever come when they might be rescued.

Brave Harry was the first to recover. Like a veteran he grasped the Professor by the hand, and wished him many a happy return of the day, and George, though not so demonstrative, joined Harry in this wish and prayer. Just then one of George's cakes fell at his feet. He picked it up and Harry glanced at the Baby. The mysterious disappearance had been solved.

No! Baby was not spanked. He came down without any coaxing, with several of the cookies in his hand, and gravely took his place at the table.

What a very narrow margin there is between tears and laughter. They roared as though such a thing as tears were unknown.

When they recovered from their fits of laughter, and attempted to proceed with the feast in some semblance of order, a glance at Baby was sufficient to start them up anew. And here a surprising thing occurred.

As before stated, he never had been known to laugh. But now Baby laughed, for the first time. And then the boys and the Professor knew that this was also the first time they had indulged in a hearty laugh.

"You may say what you please," said the Professor, "but laughter is infectious. How much farther a smile will go than a frown. And this reminds me of a very curious thing in nature. What are called perfumes have been known to carry through the air for ten miles. The odor from the balsam-yielding Humeriads has been perceived at a distance of four miles from the sh.o.r.es of South America; a species of Tetracera sends its perfume as far as that from Cuba, and the aroma of the Spice Islands is wafted many miles to sea. Now the singular thing is, that vile and injurious odors are not carried such distances."

"Why not?"

"For the reason that the oxygen of the air destroys the bad odors."

"I thought of this when we were laughing here so merrily a while ago.

Laughter is like a perfume, it goes a long way and does not need a purifying agent; but the harsh and angry word is like the evil smelling substance, which needs to be purified."

CHAPTER XI

THE GRUESOME SKELETON

The merry party lingered long over the meal. Roast prairie chicken was the chief dish. The Professor had found lentils, and this, with potatoes, or ca.s.sava, formed the princ.i.p.al dish, to say nothing of the sago pudding and the residue of the little cakes which just suited Baby's palate.

For drink there was plenty of cold water, fresh and sparkling, obtained from a natural spring not far away. The Cataract River furnished a good water, in the sense that it was clear, but it had an unpleasant taste at times, so for all cooking purposes the water used had to be carried from the spring, which was sometimes burdensome.

"I wish we could purify the Cataract water, as it would be a great convenience," was George's remark, when they were considering their work and duties.

"We can easily do that by using the chips of the common oak tree or the charcoal can be used, as I have before stated."

"It is a curious thing that oak chips will purify it. Does it act in purifying the same way as charcoal?"

"We used oak bark for the purpose of tanning leather because of the tannic acid it contained. The chips of the wood contain tannic acid as well, and it does the same thing to the impurities in water that boiling does--namely, it coagulates it. In Egypt, the muddy waters of the Nile are clarified and purified by using bitter almonds. In India, they use a nut called the Strychnos for this, purpose."