I'm glad to see the press now referring to the open-ended Richter scale.

There is another common misapprehension that the magnitude scale is itself some kind of instrument or apparatus. Visitors will frequently ask to 'see the scale.'

What emerged, of course, was that the magnitude scale presupposed that all earthquakes were alike except for a constant scaling factor. And this proved to be closer to the truth than we expected.

I repeatedly have to correct this belief. In a sense, magnitude involves steps of 10 because every increase of one magnitude represents a tenfold amplification of the ground motion. But there is no 'scale of 10' in the sense of an upper limit.

Incidentally, the usual designation of the magnitude scale to my name does less than justice to the great part that Dr. Gutenberg played in extending the scale to apply to earthquakes in all parts of the world.

We would have been happy if we could have assigned just three categories, large, medium, and small; the point is, we wanted to avoid personal judgments. It actually turned out to be quite a finely tuned scale.