>HOW do you use gravitational mass to measure a mass's mass? Use the distance, Luke. The grav attraction depends on distance raised to a power. If you can move the test body and measure force simultaneously then you have it. You could use the Moessbauer effect (in both directions, to cancel external field), to determine the potential energy difference from test mass to probe mass vs. distance I think. Peter -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu