"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 quant.i.ty of alb.u.minous matter, which is so great in quant.i.ty 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 alb.u.men 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 quant.i.ty 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."

[Ill.u.s.tration: _Fig. 27. Complete Battery with connections._]

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 princ.i.p.al parts of the boat were ready to be a.s.sembled.

"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 circ.u.mstances.

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 ma.s.s."

"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 sh.o.r.e 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."