"The liquid in the cell, marked C, is used as the electrolyte, and for that we shall take some of the sulphate of copper which the copper ore furnishes. A good strong salt solution would also answer the purpose. The two electrodes are separated, and a wire connects the two outside of the cell. Now you will notice that within the cell the current flows, as shown by the dart E, from the positive to the negative plate, but outside of the battery the current flows through the wires F from the negative to the positive plate."
"I can understand it now. The current from the battery will always go from the negative to the positive pole."
"You are mistaken. I am glad you referred to that. It shows the importance of using correct terms. You must not confound the terms 'negative plate' with 'negative pole.' All currents leave the battery or dynamo from the negative plate, but that negative plate is called the positive pole of the dynamo."
"It seems to me that is a curious way to do it."
"Such is the case, however; but there is no real positive or negative in the alternating current, so that either side may be termed positive or negative."
Work on the battery continued for some days, as lack of fine tools made much of the work difficult, and in doing this work, as in everything else, a certain amount of preparation was necessary. They had no screws, and no facilities for making them, so a substitute had to be devised, but the difficult part now to encounter was the preparation of the wire.
"A battery is of no use unless we can have wire, and it will be a big job to beat out wire long enough for our purposes," Harry observed as the battery neared completion.
"Then we must draw some wire?"
"From what?"
"From the copper?"
"Is that better than iron?"
"Copper should be used for several reasons; first, because electricity travels through a copper wire more easily than through iron, and second, for the reason that copper is more ductile than iron, and can be drawn into a wire with greater facility."
"Doesn't electricity flow through different substances at the same rate of speed?"
"Yes; but it retards the amount or the force."
"You say, 'Amount' or 'Force.' I can understand that if applied to water, that there might be a large or small quantity of water, or a greater or less pressure, but I do not see how this applies to electricity."
"In measuring the pressure of water, calculation is made by taking the height of the water in the tank. For every 28 inches in height a column one inch square weighs one pound. This represents the force of the water when it issues from the orifice below. Now the orifice may be large or it may be small. The amount or quantity which flows out is dependent on the size of the opening. Electricity is measured in a somewhat similar manner. What is called 'Volts' is the same as the force in the tank—that is, voltage means the pressure. Amperage, on the other hand, refers to the amount of current which is passing, and a greater quantity will pass over a large wire just the same as a greater amount of water will flow through a large than a small pipe. Is this perfectly clear to you?"
"Yes; I understand the difference, now."
The drawing of wire is not a difficult task where facilities are at hand, but it must be remembered that all their tools were of the crudest kind. Harry had prepared a number of bars of copper, each having been beaten out to form pieces about ten inches long and a half inch thick. A steel plate about three-eighths of an inch thick, two inches wide, and six inches long, had a number of holes bored through it, the largest hole being a half inch in diameter, and gradually increasing in size, the smallest being about a sixteenth of an inch in diameter.
When all was ready Harry was instructed to hammer out one end, so it would go through the largest hole. The projecting end was then grasped by a pair of heavy pliers, and pulled through, so that the bar was formed the size and shape of the first hole, and of course the bar was lengthened. The end was then hammered out so that it would go through the next smaller hole, and the same process was repeated, and when the wire got larger they had a tool which pushed the wire in at the same time it was being pulled out at the other side.
It was laborious work, and a long time was consumed in fully drawing out each bar. In this way a quantity of serviceable wire was prepared.
"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 principal 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 grass 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.
"Hello, and what is all this? Expecting company?"
"Yes; this is a birthday party."
"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 shores 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."
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 cassava, formed the principal 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."
"It seems people everywhere had some idea of purifying drinking water."
"Yes, and through all ages; even the Bible speaks of it."
"Where?"
"The Book of Exodus. I think the fifteenth chapter, says:
"'So Moses brought Israel from the Red Sea; and they went out into the wilderness of Shur; and they went three days in the wilderness and found no water. And when they came to Marah, they could not drink of the waters of Marah, for they were bitter; therefore the name of it was called Marah. And the people murmured against Moses saying, What shall we drink? And he cried unto the Lord, and the Lord showed him a tree, which, when he had cast into the waters, the waters were made sweet.'
"Our Cataract water, flowing, as it does, largely through forests and past vegetable banks, takes up a large quantity of albuminous matter, which is so great in quantity that the atmosphere, or the oxygen in the air, cannot purify it by the time it reaches us, so that if any astringent matter like oak, or birch, or beech, or even alum, is put in the water it will cause the albumen to precipitate. In the district of La Gironde, France, the waters of the Landes are naturally very impure from these causes, but since the cutting and floating down of the immense oak forests, the water has been made sweet and wholesome."
"Isn't all this curious and wonderful to think about?"
The work of preparing and putting into practical form the primary electric battery was going forward steadily, and at the Professor's suggestion a number of cells were made, which it might be well to describe briefly.
As the clay was the only available material, each cell had to be made rather heavy and clumsy in appearance, and was baked when completed. Each was ten inches deep and three by six and a half inches within. The electrodes, made of zinc, were each one-half inch thick, six inches wide, and nine inches long. The copper electrodes were the same dimensions, except that they were a quarter inch thick. These were stood in the cell, a short distance apart, and held in position by means of notched wooden blocks.
When all this was completed the cells were filled with sulphuric acid that had been made from the copper ore. It was, of course, much diluted with water, so as not to make it too strong.
"What is the object in making so many cells?"
"So as to get the voltage."
"Does the voltage depend on the number of the cells?"
"Each cell gives practically two volts, so that if we have 20 cells there will be 40 volts; 30 cells, 60 volts, and so on."
"But where do the amperes come in?"
"That depends on the size of the plates forming the battery. Surface is required for amperage, and quantity of plates for voltage."
"Suppose I had plates the size of this table, wouldn't I get more electricity than if I had the plates cut up into smaller pieces?"
"Electricity means both volts and amperes. There is no such thing as electricity with one of those qualities alone. A current may have 2 amperes and 40 volts, or 40 amperes and 2 volts. Multiplying the volts by the amperes gives what is called watts, and there would be 80 watts in each case."
The determination of the boys to build a new and better boat than the old one was now manifesting itself in plans, which were considered. George was in favor of building a large vessel, by means of which they could sail anywhere they wanted to; but Harry and the Professor opposed that plan, for several reasons. Harry, particularly, objected.
"I am just as anxious as George to build a large boat, but the difficulty is that to do so would take a long time, longer that we ought to take at this time. Furthermore, a large vessel would be hard to manage with our small crew, as we would have to make it a sailing vessel."
"Then why not make it a steam vessel?"
"That would make the job still harder and longer."
"I think Harry is quite right. A boat but little, if any, larger than the one we built, would be the most serviceable. If the one we made had been smaller, or lighter, we should have been able to carry it around the falls. Instead of that we had to leave it there."
Harry insisted in his views. "What we can do with our present supplies is to build a boat, even larger than our former one, and make it still lighter."
"Yes," said the Professor; "we now have lumber which is dried, and with the improvement in the tools we can turn out a boat which will be a credit to any community."
That question settled, the plan of the boat was drawn up. It was decided to build the boat on the general plan of the former one, as to size, namely, from sixteen to eighteen feet in length, and at least five feet wide, with a flat bottom, the prow to be contracted, and the bottom of the forward end to be bent upwardly, as much as their material would permit of bending.
For this purpose Harry stated that the body of the boat would be made of double thickness of material, as their sawing machinery had been so much improved that they could cut it into five-eighth inch lumber, and in that way the joints could be lapped, and the sides and bottom more easily bent into the required curves to make a graceful-looking boat.
The sawmill was at once put into good working condition, and within a week the principal parts of the boat were ready to be assembled.
"In your next weekly jaunt, I suggest that you might get our old life-boat. We should not neglect our friend."
The Professor's suggestion met with a hearty response, and on the following day the boys were off early to bring the boat to the Cataract.
First going to Observation Hill, which was the custom of one to do each day, they crawled up the rocky sides, and surveyed the horizon. From that position they could see across the neck of land, east of the Cataract, to the point southeast; to the southwest was the mountain range; to the west the forests, and to the northwest the irregular cliff line, which ended with another projecting point several miles beyond. Along the sea line this was the limit of their knowledge.
"While we are here let us examine the sides of Observation point and try to find the old flagstaff. I still think it was blown away."
Harry's suggestion was acted upon, and they made the trip together over the rocky side toward the sea. Observation point was on the mainland, and formed the extreme northern limit. It was fully half a mile from the grim rock where they had been wrecked. Between the two points were detached rocks which sprang up out of the water, and in which the water was constantly swaying to and fro. When the sea was heavy these rock islands made navigation among them a dangerous occupation.
The tide was then coming in, and eddies and cross currents were rushing hither and thither, so that it was easy to see that to float the wrecked life-boat it must be taken out to sea around the rocks. They hesitated to do this under the circumstances.
All sides of the hill were now examined with care. As they were about to leave the hill and go to the point where the life-boat lay, some wreckage was discovered below them, caught within the clefts of the rock. Here, packed in with seaweed and brush, was an object which interested them.
"What is this, George? It looks like the fragment of a boat; and here is another piece. Let us dig it out."
Both were excited beyond measure at this discovery. Not only one, but a number of pieces were finally removed. It was, beyond question, portions of a boat.
"Harry, this is part of our boat. See this piece of rope; and here is part of an oar. Wait till I get to the bottom of this mass."
"Run for the Professor, and I will remove the pieces while you are away," was George's answer.
Harry was off at the instant, and in less than half an hour, reappeared with the Professor, who examined the recovered portions of the wreck.
"It is certainly parts of a boat; but I am sure, from the present examination, that it cannot be our boat."
The boys were surprised at the information.
"My reasons for saying so," continued the Professor, "is, that the pieces here are not part of a life-boat, such as our craft was, although it was a part of a ship's boat. Where is the stern portion of our boat that you found? Let us get that, and we will be in a better condition to judge."
"We landed it beyond the point where Harry first reached the shore the day we were wrecked."
"Let us get it at once."
In less than a half hour the broken portion of the boat was landed at the foot of the cliff in front of Observation Hill.
Harry now had no doubt that the Professor's observation was correct. "See, this has no double hull, which the life-boat has, and no part of these pieces can be made to fit. Look at this stern. All of the stern post is still on the boat below."
It was, undoubtedly, another boat; but there was no name or number on any of the pieces by means of which it could be identified.
"I believe it was a part of theInvestigator'sequipment," was the Professor's final conclusion. "Have you recovered all the parts from the debris?"
"I don't think we can find anything else. While Harry was away I hunted all along the point in the hope that some more pieces might have been found."
The most minute examination was made for some mark of identification, but nothing was found which would give the least clue.
"Let us gather all these pieces and keep them for further observation, particularly for the reason that other parts may be found eventually, and identification will then be easier."
"Shouldn't we take the remnant of our life-boat to the Cataract?" asked George.
"By all means. It has just occurred to me that we might use that as part of the new boat we are building."
That was an idea which had not occurred to either of the boys. Considering that the portion recovered was the stern, and by far the largest part of the vessel, and that it had the double hull construction, made the suggestion a most acceptable one.
After all parts of the wreckage had been assembled, the Professor, accompanied by the boys, made another tour, much to the left, and on returning to the boat, the Professor's eye caught a white object lying partially hidden behind a rock.
"What is that by the rock to the right?" Without waiting for a further suggestion from the Professor, Harry made his way up, and when the object was reached, threw up his hands, without uttering a word. George had followed, and before the Professor had time to reach the spot, he cried: "A skull!"
"There is more than that," said the Professor. "Remove the debris."
The boys saw portions of the skeleton plainly now. It was such a shock to them that they could scarcely speak.
"Probably that solves the mystery of the wreckage we found."
"Undoubtedly," was the Professor's only comment.
The boys were now absolutely unnerved, but the Professor, without noticing their agitated state, carefully removed the seaweed and other accumulation, and found the skeleton largely disjointed, excepting the torso, or upper portion of the frame.
When the entire skeleton had been taken out and arranged, the Professor said: "It seems we are to have one mystery after the other."
"How long do you suppose this body has been here?"
"Probably ten months or more."
The boys looked at each other. "Ten months? That is as long as we have been here."
"That is one of the reasons why I said ten months."
The boys knew what that meant. This was, very likely, one of theInvestigator'sboats, and the skeleton the remains of one of their shipmates.
"Probably it was one of the boys," was George's inquiry.
"I do not think so," said the Professor. "The skeleton shows that of an individual past middle age."
"Why do you think so?"
"Principally, from my examination, so far, on account of the condition of the skull. You see, these saw teeth lines, which cross the top portion. These are called the sutures, and in infancy they are not joined. Before the third period of life these joints grow together, so as to form an undivided skull. But wait; here is another indication. The teeth seem to be greatly worn, showing that the person must have been close to the sixth period of life."
This discovery was the cause of very conflicting emotions in the boys. They reverently gathered the bones, and at Harry's suggestion the boys went to the Cataract for the team. The Professor volunteered to remain.
We may well imagine the feelings of the boys as they went on their mission. Here was mute evidence that others of the ill-fated ship had met disaster. They had often speculated on the fate of their companions. How many had been left to tell the tale!
The yaks were yoked, and taking with them a rude box, which had been put together, as the Professor suggested, they shortly returned.
"Have you found anything new?" was George's first question.
"The poor fellow was undoubtedly killed when he landed, and I think he was a sailor."
"Have you found anything which makes you think so?"
"Nothing but what you see before you. That break in the skull was, in my opinion, made by contact with a rock; furthermore, several of the bones were broken, as you see, at the time he met with his calamity; and one of the legs shows where it was broken before his death, and had mended."
It was a remarkable funeral cortege which wended its way slowly back over the hills to their home. They felt it was paying a tribute to a friend and companion. All doubts on their part had been dispelled. He had been one of their companions on that terrible night when the explosion had sent their ship to the bottom, and had cast them adrift on a sea which welcomed them in raging fury.
"What shall we do with the skeleton?"
The Professor was silent a long time before he answered. "I do not know what to advise. Perhaps, in the future fate may be kind enough to restore us to our homes and friends, and if it should be that we are the only ones so rescued, the skeleton would be a positive means of enabling us to ascertain whether or not he was one of our companions, and also to advise his friends."
A stone sarcophagus was built, in which the remains were deposited after a funeral service at which the Professor presided.
This event had a most depressing influence on the boys, as well it might, during the entire day, and it was the principal topic of their conversation while together. During the two days following only brief references were made to the Professor, but the second evening George's inquisitive nature could not hold in any longer.
"When we were on the rocks examining the skeleton, you referred to the fourth and the sixth ages of man."
"Yes; in point of growth man has seven ages. The first is infancy, which ends at the second year; second, the age which ends at the seventh year; third, at the end of fourteen years; fourth, at the end of twenty-two years; fifth, at the end of forty-seven years; sixth, at the end of sixty-five years; and seventh, which ends at death. These divisions vary somewhat between males and females, and I have given you merely the average between the two sexes."
"I can't help feeling sad, when I think of the things that have happened, and at the thought that all our friends may have been lost."
"Sadness is a natural feeling under the circumstances, but after all, why should it be so? Why should the sight of the skeleton bring sorrow to you? Probably the Egyptians had the right idea when they always had a skeleton at the feast."
"Skeleton at the feast? What was that for?"
"As a reminder of death?"
"There is one thing I could never make myself understand. Why is death necessary? Why couldn't man have been made so he could live always?" was Harry's query.
"You have asked a very broad question. It is one which has a great many answers. At this time I shall give only one of the reasons. The earth would not be big enough to hold the people. I do not know the population of the globe to-day. It is about 1,000,000,000; and if we take the age of the earth at only 5,000 years, we should have in that time 125 generations, counting each generation as 40 years. Do you know what that would mean in population at this time? You could not comprehend the figures. Let us take the United States alone, as an example. Assuming that the population is 90,000,000 at the present time, and that the natural rate of increase is only double in each forty years. This is how it figures out: In forty years we would have 270,000,000; in eighty years, 810,000,000; in one hundred and twenty years, 2,430,000,000; and in one hundred and sixty years, 7,290,000,000. At that rate New York City would have 480,000,000 of people and its boundaries would take in the whole of the State of New Jersey and nearly half of the entire State of New York, as thickly settled as that city now is."
"What is that weed you have, Professor? The root looks like a parsnip."
"It may be something we can drink."
"It looks just like a weed that grows all over our farm at home."
"I have no doubt of it. This is the endive, as it is known in the States, but it is really chicory."
"I have heard of chicory; isn't it used as a substitute for coffee?"
"Principally on account of the bitterness in it. The French make the greatest use of it, because they claim it gives strength to coffee."
"What part of it is used?"
"The root; the bulb you see here, and they have a curious way of preparing it. The root is dug up before the plant shoots into flower, and is washed, sliced and dried! it is then roasted until it is of a chocolate color. Two pounds of lard are roasted with each hundredweight; and afterwards, when ground and exposed to the air, it becomes moist and clammy, increases in weight, and smells like licorice. When put into cold water it gives a sweetish bitter taste, not unlike coffee."
"Let me try some of it, and don't say anything about it to Harry. And now, while I think about it, why couldn't we make some crocks out of our clay, so we can use them for our milk. We can't put them in the copper vessels and the iron is just as bad."
"That is a splendid idea; and you might as well vitrify them."
"What do you mean by vitrifying them?"
"Putting the glaze on them, just like the common crocks have."
"That would be simply fine."
The Professor explained the process, which consisted in making the crocks out of the best clay available, and then burning them. Afterwards an intense heat must be made in the furnace, and after soaking the crocks in a strong solution of salt brine, they must be put in and burned again; the greater the heat, the better.
The boys started at this with a will, and when they had arranged to make the crocks they found it most difficult to put them into a round and uniform shape.
"I would suggest that you make a potter's wheel for that purpose."
"A potter's wheel? What is it like?"
"It is the simplest thing imaginable. Do you think, Harry, you could turn out a wooden vessel just the size of the outside of an ordinary milk crock, and turn it with a central stem below, and also have a little pulley on that stem?"
The Professor made a drawing (Fig. 29), which shows just how he wanted it made. In the drawing, A is the cup-shape, which is the size and shape of outside the crock; B is the central stem; and D is the small pulley on the stem. This was mounted in a pair of arms like CC, and a belt was attached to the pulley.
"You have made a very creditable article. Now you may make a flat paddle, and shape one end so that it will be just like the inside of the crock."
The drawing (Fig. 30) shows how it was made, with a cross handle at the upper end.
That day the crocks were turned out in the following manner: The potter's wheel was rotated about sixty turns a minute, and the clay, in a plastic state, was put in the cup-shaped top, and the hands used to force the clay up the side wall. When the crock was formed in as even a manner as it could be by hand, the blade described was used to make the interior uniform.
The potter's wheel is one of the oldest tools known. Its use can be traced back for more than four thousand years, when it was well known by the Egyptians.
Since the day that the boys visited Observation Hill, at the time they discovered the skeleton and fragments of the boat, no attempt had been made to visit the cave. That was the mission when they accidentally made their surprising discovery.
George did not, however, feel that they should again make the attempt until they had a better lighting means than the unsatisfactory candles, and when the supposed petroleum vein dashed all hopes of lighting material from that quarter, the only remedy seemed to be by way of improving their candle-light.
Harry had progressed well in the making of the battery. It was now in a completed state, and he announced that the first tests would be made the next day. In the morning all assembled in the factory, and the sulphuric acid solution was made up.
The Professor inspected the batteries. Ten cells had been prepared, so that they could have, at least, fifteen volts. When all the cells had been connected together—that is, the positive pole of one cell with the negative pole of the other—a wire was attached at each end of the row of cells, at the last electrodes, so as to form the outside connections.
When the two outside wires were brought together and their contact broken a spark was plainly shown, which was an indication that the battery was generating electricity. The boys danced about with joy at this exhibition. From that time forward the battery was one of the most interesting things in the laboratory, and what they finally accomplished with it will be fully detailed as we go along in their history.
George thought he saw a way to make the light necessary for the cave. "Why can't we rig up an electric light now and explore the cave?"
"We might do that, but we have several things to do before we can have light from that source."
"Haven't we the electricity for it?"
"Do you know how many years electricity was known before electric light was discovered? Before we can utilize this agency for lighting purposes, we must make a machine which will produce a vacuum; we must make glass; we must learn to carbonize threads; and the art of blowing glass would be a necessary accomplishment."
"As usual," said Harry, "something must be made to make something that makes something else."
"But can we make electric light without putting it in a glass bulb?"
"Yes; we can make what is called the arc light; instead of the incandescent."
"What is the difference between the two?"
"In the incandescent, such as we talked about making, a thin carbon filament is enclosed in a glass bulb, from which as much air as possible has been exhausted, and when a current of electricity passes through this filament, it is heated up to a white heat."
"Why doesn't it burn out?"
"It does burn out in time. What preserves it, however, for a long time, is that most of the oxygen has been exhausted from the bulb——"
"Oh, yes; I know, there must be oxygen to support combustion, so that the carbon is merely heated up?"
"I am glad you remembered that. The arc light, on the other hand, depends on an entirely different thing. You have seen, no doubt, the long black pencils used in the large lamps. That is carbon also, made out of ground coke, molded and compressed into shape."
"What does arc mean!"
"Did you notice that when we put together the two circuiting ends of the wires in our battery this morning, we could not notice the existence of a current, but whenever we pulled them apart we had a spark?
"Let us now make a little experiment which will show you the arc. You see, I am making a sharp point at the end of each wire, and I will fasten one of the wires so it cannot be moved. Now the other wire will be placed with its point as close to the other points as possible, and so fixed to the support that we can adjust it still closer and hold it. See, the points now touch each other. I will move one of the wires the slightest distance away from the other. There! see the light?"
"But it goes out in a little while; what is the cause of that?"
"The electricity has been burned off the end of the wire, and the distance is now too great for the electricity to jump from one to the other, so they must be moved closer together. That space between the ends of the two wires is the electric arc. Instead of the two wires the carbon pencils are used."
"But how are the two carbon pencils kept apart at the right distance at all times?"
"That is what the invention of the arc light consisted in; to find a means whereby the current itself makes the adjustment necessary to furnish a steady, constant light. When we start to make the arc light the mechanism can be explained."
George's scheme of the electric lamp for the cave had vanished. But the cave must be explored. He was determined on that point.
The yaks were brought out and a start made for the cliffs. After unhitching them from the wagon and unyoking the animals, so they could feed in the meantime, the oil lamps were taken out and carefully examined. The Professor had suggested the advisability of carrying with them two of the spears, which, it will be remembered, formed part of the weapon equipment of their last voyage, and those, with the guns, were considered sufficient for any foe likely to be in the cave.
Harry, on this occasion, volunteered to mount Observation Hill for their daily trip of observation. He returned by the time the yaks were disposed of and the implements prepared, as stated.
"I suggest," said the Professor, "that we keep constantly on the alert now for any vestiges of driftwood, or other objects which we are likely to find along the shore."
As a result the progress was slow, and the scrutiny keen on the part of all. As they rounded the last large projecting rock, just before entering the gorge which led to the cave, Harry jumped on a rock, waving his hand, and crying, as he pointed seaward: "A sail! A ship! See it?"
The agitation of George was beyond all description. Harry kept repeating the words. He was entirely beyond control.
"Be calm; do not become excited. Harry, you are the most nimble; run to Observation Hill: here take the large sheet in the wagon; wave it there, and keep up the signaling; they may see you."
The ship, although far away, was plainly made out, but its character could not be determined. It was evidently a large sailing vessel. Just imagine what must have been the feelings of the party at the sight of the ship, although so far away. Would they see the signal?
In the commotion that followed, what was the Professor doing? He quickly placed two stakes in line with the ship, and watched it patiently. "It is moving to the west."
George's curiosity induced him to look over the Professor's shoulder, and thus enable him to follow the movement of the boat, and by means of which he could see the sails slowly move past the distant stake.
The Professor scarcely moved. "What is Harry doing? Is he still signaling?"
"Yes; he hasn't stopped since he reached the hill."
The stake nearest the Professor was again moved over a trifle as the ship moved on, and they watched and waited.
"Why, the ship hasn't moved for the last ten minutes."
"It seems not," was the Professor's response. Again they waited. George walked to the stakes and back again. He stepped aside to look at Harry on the hill, and again returned to the observation stakes.
"Singular that the ship hasn't moved in twenty minutes or more."
Then, enthusiastic at the mere thought, he cried out, as he ran toward the Professor: "Do you think they have seen our signal? Have they stopped; and are they returning?"
"Either that or they have changed their course, and are now leaving us dead ahead."
This was a blow to the poor boy, whose hopes, brought about by the apparently checked motion of the ship, were now dashed to the ground, when the Professor continued: "They are sailing away, I am sorry to say."
He left the observation stakes. Poor Harry was still signaling frantically. The Professor told Harry that further effort in that direction would be useless, and he slowly and sadly came down the hill.
They looked at each other most sorrowfully, and the boys could scarcely restrain their tears, while the Professor carefully avoided their gaze, or seemed not to notice their grief.
"It is one satisfaction to know," said Harry, as he dolefully looked across the broad sea, "that vessels do come this way, and that it is not out of the world entirely."
George quickly recovered. "Why not make a big signal flag for Observation Hill?" This was seconded by the Professor.
"And while we are about it why not make a good old American flag?" was Harry's comment.
The cave had been forgotten in this incident. When their wondering and questionings had ceased, the descent was made around the point, and the entrance soon reached.
The two lamps were now lighted, and the explorations began.
"I think it is advisable," was the Professor's first observation, "that we go in a hundred feet or so, and then mount one of our lamps in a conspicuous place. We can then proceed with the other as far as the water, and if any accident happens it will not cause trouble to both of the lights. We can always have one of them to fall back on."
When they had gone the distance determined on, a secure ledge was selected, and Harry placed the light so it would cast its beams along the cave.
"Be careful now, we are near the water."
The Professor had now the other light, and the boys led the way, so the beams from the light shone past ahead of them. They went beyond the point where the water had been found previously, but there was no sign of it. The course of the cave now changed to the right, and the floor of the cave went downwardly at a slight descent.
The Professor suddenly restrained the boys. "Wait a moment; the light behind us should be brought forward to this point."
George went back and brought it up, and after some delay a place for it was found. The two lights now plainly showed a sudden enlargement in the area of the cave, and above them hung what appeared to be huge icicles, giving the interior a weird appearance. Still no water was in sight.
"The white substances we see all around us indicate that above us the rocks are limestone, and water, in coming through, has acted on the stone so as to form carbonate of lime, or chalk."
The single lamp was now sufficient to light up the interior, which looked like a domed iceberg, with all sorts of fantastic figures standing out in bold relief, which were contrasted by the many dark recesses irregularly scattered about everywhere.
"I see an opening beyond," was Harry's remark, in a suppressed tone.
The contracted opening was to the left, and he quickly made his way over the uneven floor to that point. "The water is beyond, and I hear something there."
George quietly moved forward. The light from the Professor's lamp glistened on the surface, and rippling waves were easily distinguished.
"What has become of the light we had on the perch?" was the Professor's startling inquiry.
The boys looked back. It was not there. Probably it had gone out.
"We must not go on until we have relighted it," was the Professor's caution.
George went back. The light from the Professor's lamp still threw its rays back to the ledge, which was not more than a hundred feet from their present location. "I can't find it. It is not here, and I know I put it on this ledge. Here is the piece of lime I put up against it."
Too startled for words, Harry drew back from the opening. Without further conversation he and the Professor retraced their steps toward George, who was now frantically searching every crevice.
"That is too bad. Are you sure this is the place?"
"I am positive of it."
The boys looked at the Professor. He knew they mentally asked whether they should proceed with the single light. "I think it would be unwise to go farther with one light only. If we can do no better we can make a half dozen lights, and light up the whole cave. I am just as much interested in it now as you are."
They were about six hundred feet from the mouth of the cave, as nearly as could be estimated.
"Before we return we might as well chart the cave, so we shall have some idea of its crooks and turns. Have we anything to measure with? If not, have you a cord, so we can get some idea of distances?"
George held out one of the spears, which was about five feet long.
"That will answer," said the Professor. "Let us call this five feet long for the present. The first thing we must do is to establish a base line. But what shall we do for something to mark our chart on? I haven't a bit of paper."
Here was another difficulty. It would be impossible to make tracings on their clothing. Harry's wit came to the rescue. "I have it. Why can't we break off a piece of this chalk. Probably we can find some smooth piece that will answer."
"That might be done," was George's answer, on reflection; "but what can be used to mark on chalk?"
The Professor was now highly amused. "Can't you think of anything we have here which will answer?"
"I haven't had a pencil, or anything except charcoal, since we touched this wonder island."
"We have something here that is used among all civilized people the world over for marking purposes." The boys opened their eyes in wonder. "I have it here," said the Professor, looking at the lamp.
"The lamp?"
"No, not the lamp, but what is in the lamp."
"The oil? Where can we get anything to mark with in the oil?"
"We have been making a marking material all the time we have been in the cave, and you are just as well acquainted with it as anything you know. It is the soot from the burning oil."
The boys laughed, not at the information, but at their stupidity.
"Yes; the soot is carbon, and the best soot is made by imperfectly burning oil, or fat, or any other fuel which has a large amount of carbon."
The boys found several pieces of flat chalk, one of them a little over a foot long. This was held above the flame of the candle until covered with soot.
"The first thing to do is to establish a base line. This we will mark A on the drawing. Now, starting from the point here where we lost the light, you may measure along the line to the west, we will say, until you get to the other end of the chamber. Twenty-five measures of the spear? That makes the chamber 125 feet long, and it is about 90 feet the other way. Let us roughly outline the floor plan. Now go out toward the mouth of our cave, and measure off 50 feet. Stop there. You see, I have marked the line A and have laid down the slate slab so that this line is exactly on a line with the one you have measured along the chamber. The point B, 50 feet from here, which you have just measured, makes an angle, C. I will now take the slab to the point B, and you may measure off 50 feet more, and we will call that D. That gives us another angle line, E. You see, at every point we establish a new base line. C is the base line for the line E, and so on all through the cave."