Some time ago, Stephen Davis wrote that the international prototype kilogram is: > ... a solid cylinder of platinum-iridium alloy maintained at constant > temperature at S�vres near Paris. I don't believe the prototype kilogram is kept at constant temperature. Mass does not depend on temperature, so what would be the point? The earlier prototype for the metre was a platinum-iridium bar on which two marks near ether end were defined to be 1 metre apart. The temperature of that bar DID have to be at a specified temeprature WHEN IT WAS USED FOR MEASURING because the length of the bar would vary with temperature. (However, even here, I don't see why the bar would need to be kept at a constant temperature when it was merely being stored and not at that moment being use to measure anything.) The prototype metre was later replace by other better standards, most recently by the distance light travels in vacuum in a specified fraction of a second. Regards, Bill Hooper ============ Keep It Simple! Make It Metric! ============
