This was repeated over and over a great many times, and finally the hard steel bar was found to have a charge of magnetism, and for the purpose of providing a means for holding the magnetism, a C-shaped piece of iron was put on the bar, as shown in the detached figure.
"Is that the reason," asked Harry, "why a small piece of metal is always put across the ends of a horseshoe magnet when it is not in use?"
"Yes."
CHAPTER X
STARTING ON THE VOYAGE TO THE WEST
"If I remember correctly, you stated some time ago, Professor, that the barometer indicated the pressure of the atmosphere, and in that way it was useful in letting us know what the weather would be. Before we sail, would it not be well to make one of them? If we had possession of one of the articles, we might not have been caught in the storm the first time we took out No. 3."
"That is a good suggestion. I intended to propose that, because with the barometer and the compass we shall be equipped with two of the most useful instruments needed."
"I cannot comprehend how the air pressure has anything to do with the weather. Is the air pressure really greater at one time than at another?"
"Heated air ascends, does it not?"