Things started falling back into place in the sixteenth century when Nicolaus Copernicus appeared on the scene. In 1543 he presented the theory that the Sun, not Earth, was at the center of the universe. Although still incorrect, his theory at least made room for an explanation of the seasons, and he correctly deduced that Earth rotated on its axis once a day and made the long trip around the Sun once each year. This was a scandalous and shocking idea at the time, because it contradicted religious dogma and suggested that man was just a part of nature, instead of being superior to it.
Leonardo da Vinci was fascinated by the weather. He noticed that a ball of wool weighed more on a rainy day than on a dry one, and further experiments led to his invention of the hygrometer, a device to measure the amount of water suspended in the air. Da Vinci wasn’t content to measure the air’s water content; he also invented the anemometer, which measures wind speed.
Even though the air’s moisture level and speed now could be measured, for most of the sixteenth century no one could tell you how hot it was, because there were no thermometers yet. Enter Galileo Galilei, who remedied the thermometer shortage in 1593.
Galileo called his invention a thermoscope. It consisted of a long-necked glass bottle that was placed, upside down, into a vessel containing water. When the bottle was heated slightly, usually by the warmth of the experimenter’s hands, the air inside expanded and the water was pushed downward. When the bottle cooled, the air contracted and the water rose back up into the neck of the bottle. Unfortunately, the thermoscope had no degree markings and was useless for determining temperature, but it paved the way for the more accurate versions to come.
Now one could tell how humid it was and how fast the wind was blowing, and could get a vague idea of the temperature. But what about the air pressure?
Evangelista Torricelli, a student of Galileo’s, created the first mercury barometer to measure atmospheric pressure in 1644, completing the list of instruments needed to develop an accurate weather forecast.
Aristotle’s contention that “nature abhors a vacuum” could be debated but not tested until Torricelli created one inside his mercury barometer. Catholic Jesuits, alarmed by this breach of faith, theorized that the mercury was being held up by invisible threads. But by then there was no stopping the weather revolution.
A French mathematician, Blaise Pascal, theorized that if air had weight, it should exert less and less pressure the higher you went. In 1648 he convinced his brother-in-law, armed with one of Torricelli’s barometers, to climb almost 5,000 feet up a mountain. Sure enough, the higher he went, the lower the mercury sank.
The first recorded weather observations in the New World were made by a minister named John Campanius Holm in 1644 and 1645. Some people consider Holm, who lived in the colony of New Sweden near Wilmington, Delaware, to be America’s first weatherman. In fact the National Weather Service gives an award in his name to outstanding volunteer weather observers each year.
Have you ever wondered why the United States uses a method of measuring temperature that’s different from the one used by the rest of the world? Blame Daniel Gabriel Fahrenheit, a German instrument maker who, in 1714, came up with the temperature scale that bears his name. He based his system on the difference between the freezing point of water and his own body temperature. Sound arbitrary and confusing? Indeed.
The Fahrenheit scale is considered antiquated by scientists, who use the Celsius scale instead and wish everyone else would too. Old habits die hard—it’ll probably be some time yet before everyone’s on the same page temperature-wise.
Not content to leave well enough alone, Swedish astronomer Anders Celsius proposed another method. He divided the freezing and boiling points of water into equal degrees, which he called the centesimal system. Celsius decided the boiling point of water would be 0°, and the freezing point would be 100°. That must not have made any more sense at that time than it does now, because after his death, the scale was turned upside down, creating the measuring system still used today.
In 1793, Englishman John Dalton wrote a book called Meteorological Observations and Essays in which he advanced the theory that rain is caused by a drop in temperature, not air pressure. Taking the next step, he realized in 1802 that temperature actually affects the amount of water vapor the air can hold, a concept now called relative humidity.