It is odd to think that there is a word for something which, strictly speaking, does not exist, namely, 'rest'. We distinguish between living and dead matter; between moving bodies and bodies at rest. This is a primitive point of view. What seems dead, a stone or the proverbial 'door-nail', say, is actually forever in motion. We have merely become accustomed to judge by outward appearances; by the deceptive impressions we get through our senses.