Earthquake force or magnitude is a favorite topic of discussion among the west-coasters subjected to the occasional shakers. But what does it really mean when a quake is, say, 5.5. in magnitude as opposed to a 7.1? That was the general question Charles Richter set out to solve with his patented Richter Scale, which was inspired by his study of radio waves. Richter later said earthquake waves were a lot of radio waves, emanating out from a a central location. Their strength could be measured in a similar way.

On this day, April 26, in 199 Richter developed his famous scale, consists of a secure frame from which a weight hung held in place by inertia. Any ground movement would set off the weight, which would transfer onto a stationary piece of paper the “amplitude”, or ground displacement of the seismic wave.

At the suggestion of one of this advisers, Richter made the scale logarithmic, meaning each full step in magnitude (from 5.0 to 6.0) indicates a tenfold jump in power.