"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?"