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LESSONS

IN

ELEMENTARY

PHYSICS.

INTRODUCTION.

1. Definition of Physics.-As we look around on the universe in which we dwell, we are struck with a variety of objects outside of ourselves and independent of us. Some of these we see, some we hear, others we touch, or taste, or smell, while many appeal to various senses at once.

When quite young we begin to reason upon these impressions, and the constant recurrence of phenomena in a certain order gives us a well-grounded expectation that in future the same order will be observed. As night approaches, the sun appears to sink below the horizon, and so to vanish from our sight; and yet, from past experience, we have the most perfect confidence that he will reappear on the morrow. But while all classes of men in every age acquire from the necessities of life a certain knowledge of the laws which regulate - the phenomena around them, this knowledge is nevertheless most superficial and imperfect. A child knows that a stone will fall to the ground, but it required a Newton to discover the law of gravitation.

It is only within the last three centuries that men have

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