It is not enough to describe some objects by their location. We may also need to know its direction. For example, a wind blows a storm over your school. Where is that storm coming from? Where is it going? How can we describe a direction? The most common way is by using a compass. A compass is a device with a floating needle (Figure 2.1). The needle is a small magnet. The needle aligns itself with the Earth's magnetic field. The compass needle always points to magnetic north. If you have a compass and you find north. You can then know any other direction. See the directions, such as east, south, west, etc., on a compass rose. The Earth has two poles. It has a magnetic north pole. It also has a geographic north pole. These two poles are close to each other but not the exact same place.

What is the most common way to determine direction?

Earthquakes seemed to outline a special feature of earth's crust. Earthquakes let scientists know where the crust was moving. This led to the discovery that the Earths crust was broken up into regions, or plates. Earthquakes happen most often along these plate boundaries. This was evidence that continents can move. The movements of the plates are called plate tectonics. The Earths crust is divided into plates. There are about a dozen large plates and several small ones. Each plate is named for the continent or ocean basin it contains. Scientists know he plates are in motion. They now know the direction and speed of this motion . Plates dont move very fast. They move only a few centimeters a year. This is about the same rate fingernails grow. So you might wonder, what could cause this motion? What supplies the energy to cause this change?

Why is it likely that scientists only learned about plate boundaries from studying earthquakes?

His exile lasted nearly a year and a half. Long before that time there had come a reaction in his favour. The new consuls were well disposed towards him; Clodius's insolence had already disgusted Pompey; Caesar was absent with his legions in Gaul; his own friends, who had all along been active in his favour (though in his querulous mood he accused them of apathy) took advantage of the change, his generous rival Hortensius being amongst the most active; and all the frantic violence of Clodius and his party served only to delay for a while the return which they could not prevent. A motion for his recall was carried at last by an immense majority. Cicero had one remarkable ally on that occasion. On one of the days when the Senate was known to be discussing his recall, the 'Andromache' of Ennius was being played in the theatre. The popular actor Esop, whose name has come down to us in conjunction with that of Roscius, was playing the principal character. The great orator had been his pupil, and was evidently regarded by him as a personal friend. With all the force of his consummate art, he threw into Andromache's lament for her absent father his own feelings for Cicero. The words in the part were strikingly appropriate, and he did not hesitate to insert a phrase or two of his own when he came to speak of the man
On one of the days when the Senate was known to be discussing his recall, the 'Andromache' of Ennius was being played in the theatre. Who was playing the principal character?