196 The Stock Market Crash—dAnd After
science into business management, trade union policy,
and government administration. Concrete instances
of technical improvements in many mining, metallurgical,
 and fabricating processes are given in the chapters
 on industry. The remarkable results achieved
are demonstrated statistically from census data showing
 output per worker. Similar, though less striking,
 instances appear in the chapter on construction.
Without help from any extraordinary invention, the
railroads, also, have attained a higher level of operating
 efficiency. In farming there is an intriguing
report of new machines and new methods coming
into use. Here, too, the record of average output
per worker shows considerable gain.
“All this means that since 1921 Americans have
found ways of producing more physical goods per
hour of labor than ever before. They have received
larger average incomes because they have produced
more commodities and services.”
It was in this intensified upthrust of forces making
 for increased productivity per worker during the
past seven years that the secret of the long bull market
 stands revealed. From this increased productivity
 came a more rapid increase of earnings of
corporations, together with the ‘“‘plowing-back” of
earnings in expectation of greater future gains. This
expectation made men content to invest their money
for smaller immediate dividends and at higher prices
for corporate securities than past earnings had
warranted.
A further reason was in the reduction of risks due