PASCAL'S PRINCIPLE
Imagine you could go into this piece of glass, and travel about in the
red fluid.
When the fluid was poured into the left tube, it filled all 4 tubes up
to the same height.
If you went to the bottom (horizontal) part of the tube, do you think you
would feel more pressure if you were under any specific tube?
No, you would not feel any difference. The pressure you'd feel depends
only on your depth... remember the equation Pressure=Dhg. The equation
takes into account only gravity, depth, and the density of the fluid.
The particles of the fluid transmit the pressure to neighboring particles
throughout the fluid.
Blaise Pascal was a really smart guy. Here is a site made by
a fan of his. It describes some really wild math that Pascal thought
about, 300 years ago: http://members.tripod.com/~absolutebow/ptri2.html