In my early days of television I had the pleasure of interviewing Dr. Russell Maag of N.W. Missouri State University. Dr. Maag believed that the thickness of animal pelts and years of abundant harvests targeted episodes of droughts. His research suggested that tree rings could serve as a model to the type of weather experienced at a given time in a specific area.  Thickness of the ring could explain an abundance of precipitation while a thinner ring suggested a deficit.  Climate-sensitive tree ring records were analyzed for Mexico and matched the infamous "Famine of One Rabbit" in 1454. "One Rabbit" is the first year of the 52-year Aztec calendar cycle and folklore suggests that famine and catastrophe occur in its return.  The tree ring data showed that a severe drought occurred before ten of the 13 One Rabbit years or around A.D. 882 to 1558.  This evidence suggests a climatological match to the curse. From tree rings and rabbits to pressure... Atmospheric pressure is the force exerted on the surface from the weight of air above the surface. We wouldn't know this if it weren't for events that took place at the Puy de Dome Observatory in Central France. The atmosphere is a fluid layer of gases, surrounding the earth with a total weight of 5,600 trillion tons. At sea level, a vertical column of air one inch square, rising to the atmosphere weighs 14.7 pounds. French scientist and philosopher, Blaise Pascal didn't know this in 1648 when he instructed his brother-in-law to carry a barometer from the base of the Puy de Dome, 1465 meters to its summit which resulted in a fall of three inches of mercury. This established the rate of variation of the Earth's atmospheric pressure due to altitude. Two-hundred years later the Puy de Dome Observatory became the first permanent mountain observatory in Europe.