We went to Threlkeld Quarry to see a steam digger. Steam driven pistons can only move in a straight line. But the hydraulics on this old JCB are an improvement. Water is incompressible. The molecules are so close together that there is no space between them into which they can be squashed. This means that water transmits pressure. If you push on one side, you also push on the other side. Water pressure acts equally in all directions - up and down and sideways. So pushing on one end of the hydraulic fluid in the black pipes means that a push is generated at the other end as well to move the digger arm. The black pipes go round the corner but the pressure is still transmitted because of the way that pressure acts in all directions.
