The measurement of G

The measurement of G, the Newtonian constant of gravitation, is a long standing problem which still continues to provide a challenge to our scientific creativity. A brief review of the history of G measurements is given. Today, the nearly 1% discrepancy between the recent PTB (Physikalisch-Technische Bundesanstalt) measurement and the "accepted" value of G is of considerable interest to the world of standards. The fact that the PTB measurement appears to be competently and thoughtfully done makes the discrepancy even more intriguing. Finally, a new free-fall approach (using g to measure G) is described. In this proof-of-concept experiment, an FG5 absolute gravimeter is employed in connection with a movable 100 kg mass that surrounds the dropping chamber. Little g is measured when the surrounding mass is located above the FG5\´s dropping region and then when it is located below the dropping region. The difference in these two measurements together with the geometry of the surrounding mass can be used to determine G. The status of this work and prospects for future improvements using this technique are discussed.