Shrinking Kilogram Bewilders Physicists

Physicist Richard Davis of the International Bureau of Weights and Measures, sits next to a copy of a 118-year-old cylinder that has been the international prototype for the metric mass, in his office in Sevres, southwest of Paris, Wednesday, Sept. 12,007. Davis said the reference kilo appears to have lost 50 micrograms compared to the average of dozens of copies. The kilogram's inconstancy illustrates how technological progress is leaving science's most basic measurements in its dust. (AP Photo/Jacques Brinon)

(AP) -- A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight - if ever so slightly.