Anyone who has ridden on a railroad train knows how rapidly another train【36】by when it is traveling in the【37】direction and conversely how it may look almost【38】when it is moving in the same direction.【39】a train at a station starts to move forward【40】gently that passengers feels no backward movement【41】.Then if they happened to【42】the window and see another train slide past on the next track, they have no way of knowing【43】train is in motion and which is at rest【44】can they tell how fast either one is moving or in which direction The only way they can judge their【45】is by looking out the other side of the car for some fixed body of reference【46】the station platform. or a single fight. Newton was【47】these tricks of motion, only he thought in terms of ships. He knew that on a calm day at sea a sailor can shave himself or drink soup as【48】as when his ship is lying motionless in harbor. The water in his basin, the soup in his bowl, will remain【49】whether the ship is making five knots, 15 knots or 25 knots. So【50】he looks hard at the sea it will be【51】for him to know how fast his ship is moving or indeed if it is moving at all. Of course, if the sea should get rough or the ship changes course suddenly,【52】he will sense his state of motion. But even supposing that we have the idealized conditions of a glass calm sea and a silent ship, nothing that happens below decks -- no amount of observation or mechanical experiment performed inside the ship --will reveal its velocity through the sea. The physical【53】based on these facts was formulated by Newton in 1687.'The motions of bodies included in a given space , he wrote, 'are the same【54】themselves, whether that space is at rest or moves uniformly【55】in a straight line.' (66)