MAGNETISM.

Q. What is magnetism?

A. It is that science which treats of the properties of the magnet or loadstone.

Q. What is the magnet or loadstone? A. It is an ore of iron found in the iron mines of Sweden and Norway. It is also found in Arabia, China, and other countries in Asia.

Q. Mention some of the properties of the magnet.

A. It attracts iron, points to the poles, and dips or inclines downwards.

Q. Can the loadstone communicate these powers to iron or steel?

A. Yes; a piece of iron or a piece of steel will be magnetised by being rubbed against a loadstone. A light and slender piece of steel, as a sewing-needle, may be magnetised by simply touching a good loadstone.

Q. Can iron or steel be magnetised in any other way?

A. Yes; by being struck with a hammer.

Q. What is an artificial magnet?

A. A piece of steel or iron to which the properties of the magnet have been communicated.

Q. What is the tendency which the magnet has of pointing towards the poles called?

A. Its polarity.

Q. What are the two ends of a magnet called?

A. Its poles; the end pointing to the north being called its north pole, and the end pointing to the south its south pole.

Q. What is the axis of a magnet? A. The straight line joining the two poles is called the axis of the magnet. Q. How can the polarity and dip of the magnet be shown?

A. If a light and slender bar of magnetised iron be placed so as to be able to move freely in any direction, its north pole will be found to point to the west of north, and to dip or sink, and its

south pole will be found to point to the east of south, and to be elevated.

Q. What instrument is founded on the property which the magnet possesses of pointing towards the north and south? A. The mariner's compass.

Q. What is the mariner's compass? A. It is a needle or small bar of steel which has been made magnetical. Q. For what is it used?

at sea.

A. To point out the course of a ship The mariner's compass has probably done more to extend commerce, to promote manufactures, and to civilize mankind, than any other scientific dis

covery.

Q. Cannot the mariner find out his course at sea by any other means than the magnet?

A. Yes; he can do so by means of the heavenly bodies, but when these are obscured by clouds, he cannot find out his course without the compass.

Q. Were long voyages undertaken before the invention of the mariner's compass?

A. No; for the mariner durst not then

lose sight of the coast, for fear of mistak ing his course if the sky should become clouded.

Q. Does the mariner's compass point exactly north and south?

A. No; it possesses the properties of the magnet, and it is found that in Europe its north pole points to the west of north, and its south pole to the east of south. This deviation from the true north and south is called the deviation or variation of the compass.

Q. Who first observed the deviation of the compass?

A. Columbus in his first voyage observed the deviation of the compass as he advanced across the Atlantic Ocean.

Q. Are the deviation and dip of the compass always the same?

A. No; they vary at the same place at different times, and in different places at the same time.

Q. Who first observed the dip of the compass?

A. A person named Robert Norman, in the year 1576.

Q. Do the changes in the deviation

of the magnet take place rapidly at the same place?

A. No; they take place very gradually at the same place. The change which takes place at the same place even in two or three years is not great.

Q. Since the direction in which the magnet points is different at different places at the same time, how can the mariner rely on the compass to tell him the course in which he is sailing?

A. Mariners are furnished with charts which tell them the variation of the compass at the different places on the earth, with sufficient accuracy to enable them to find out their course.

Q. Are there any places on the earth's surface where the compass points exactly north and south, and where it does not dip?

A. Yes.

Q. Does the magnet possess any other property?

A. Yes; if the two north or the two south poles of two magnets, freely suspended, be brought together, they will