  The minute fluctuations of of S&P 500 and NASDAQ 100 indices display
Boltzmann statistics over a wide range of positive as well as negative returns,
thus allowing us to define a {\em market temperature} for either sign. With
increasing time the sharp Boltzmann peak broadens into a Gaussian whose
volatility $ \sigma $ measured in $1/ \sqrt{{\rm min}}$ is related to the
temperature $T$ by $T= \sigma / \sqrt{2}$. Plots over the years 1990--2006 show
that the arrival of the 2000 crash was preceded by an increase in market
temperature, suggesting that this increase can be used as a warning signal for
crashes. A plot of the Dow Jones temperature over 78 years reveals a remarkable
stability through many historical turmoils, interrupted only by short heat
bursts near the crashes.
