Quotes About Mercury

Can you imagine my joy at the feasibility of the general covariance with the result that the equations of the perihelion movement of Mercury prove correct? I was speechless for several days with excitement. (Einstein to Ehrenfest)

Of course, in an ideal world we'd be using mercury as the propellant fluid, but even that has handling problems, not to mention cost and sourcing for the kind of volume we're looking at. So what we've wound up with is a very dense hydrocarbon, it's almost pure crude oil, but the chemists have tweaked the molecular structure so it remains liquid over a huge temperature range.