The Handy Math Answer Book

everyone, with some dishes and windows broken, unstable objects overturned, and
disturbances of trees, poles, and other tall objects sometimes noticed.

But scientists wanted a more solid, less subjective scale. One of the first scales
developed to measure the true magnitude was invented by American seismologist
Charles Francis Richter (1900–1985) and German-born seismologist Beno Gutenberg
(1889–1960). In 1935 these scientists borrowed the idea of magnitude from
astronomers (stellar brightness is measured by magnitude), defining earthquake mag-
nitude as how fast the ground moved as measured on a particular seismograph a spe-
cific distance from the quake’s epicenter.

The Richter Scale is not a physical scale like a ruler, but rather a mathematical
construct—it is not linear, but logarithmic. Thus, an increase in each whole number
on the scale represents a ten-fold increase in power. Its numbers represent the maxi-
mum amplitude of seismic waves that occur 62 miles (100 kilometers) from the epi-
center of an earthquake. Because seismographs are usually not located at this exact
interval, the magnitudes are deduced using the arrival of specific waves of energy
given off when an earthquake occurs. 301

MATH IN THE NATURAL SCIENCES

What is Mohs’ Scale of hardness?

M

ohs’ Scale of hardness (also seen as Mohs Hardness Scale, Mohs Scale, or

even erroneously as Moh’s Scale) was invented by German mineralogist

Friedrich Mohs (1773–1839). This arbitrary scale measures hardness or the

scratch resistance of minerals and is often used as a quick way to help identify

minerals in the field and laboratory. But the numbers assigned to the various

minerals are not proportional to their actual scratch resistance. Thus, the main

reason for using the scale is to know that a mineral with a lower number can be

scratched by a mineral with a higher number.

Mineral Hardness

talc 1

gypsum 2

calcite 3

fluorite 4

apatite 5

orthoclase 6

quartz 7

topaz 8

corundum 9

diamond 10