The easiest way to determine the polarity of an unmarked magnet are marked. As a rule, the North pole of the magnet, note blue paint, southern, accordingly red. Since like poles repel each other and unlike attract each other, it is enough to see which pole of your magnet will be repelled from the North pole reference, to determine where, and what.
For the same purpose you can use the compass, which, in fact, represents a magnetic needle, freely rotating on the axis. Bring your magnet to the compass and see what it pole will attract the North end of the arrow. This will be the South pole of your magnet.
If you have no compass, you can make yourself, but this will require the ability to navigate the terrain. After the magnet a few times with an iron needle, you will magnetize it. Then lubricate the needle with any oil, put it on the water surface, poured into a saucer. If the saucer is wide enough, and not near strong magnets, the arrow will point one of its ends to the North. To determine where North is and where South is possible, for example, the sun in the Northern hemisphere it most of the year is moving along the South side of the sky. You can then check the polarity of your magnet the same way as with a conventional compass.
Force field lines enter the South pole of the magnet in and out of the North, as if revolving in a circle. Electric charge is caught in this field will follow the movement of lines.

Sprinkling some powdered sugar in a clean and dry plastic jar, close it and how to shake until the powder will not get electrified. exactly and don't start sticking to the walls of the jar. So you get positively-charged dust.

Put the magnet on the table so that its poles were in a horizontal position. Magnet from a speaker, for example, it will have to put on an edge. Then pour a little of the charged dust in the air above a magnet. Motes spun along the lines of.