In 1654, Otto von Guericke, burgomaster of Magdeburg, performed an experiment using two brass hemispheres which fit together closely to make a sphere and which could be evacuated with a vacuum pump, which von Guericke had invented in 1650. Von Guericke used hemispheres about fourteen inches in diameter, and when as much air as possible had been pumped from them, two teams of horses could not pull the hemispheres apart. The hemispheres shown here were purchased for $6.00 in 1885. __________________________________________ Mayor Otto von Guericke of Magdeburg (1602-1686 AD) clearly had a flair for the dramatic. His scientific demonstrations involved props such as guillotines and strongmen. But his most famous public experiment at Regensburg sometime around 1654 (the exact date is uncertain) included what came to be known as the Magdeburg hemispheres. Made of copper or brass, the hemispheres can be joined to form a hollow globe. Using an air pump (which von Guericke also invented), he removed the air from the sphere and showed how 16 horses – 2 teams of 8 each – could not pull the halves apart. The sphere immediately fell apart once air was reintroduced. From this experiment, he showed that the air pressure surrounding the hemispheres, without the counteraction of the pressure normally existing inside the sphere when it was filled with air, made them cling together. Scientists were just beginning to realize that we live under an ocean of air, with the mass of the atmosphere corresponding to a pressure of about 1 kg per cm2. The discovery of the sheer force of the pressure of the atmosphere led to the development of the first steam engines in the 1700s. Although the 1600s were a tumultuous time in Magdeburg’s history, von Guericke still found time to contemplate various questions about the nature of space. Aristotle (384-322 BC) proposed that “nature abhors a vacuum,” currently defined as any volume with a lower particle density and gas pressure than the surrounding atmosphere. This postulate would be believed for almost 2000 years. Evangelista Torricelli (1608-1647 AD), one of von Guericke’s contemporaries, demonstrated in 1643 that a vacuum could exist in space above an enclosed column of mercury. However, from astronomical observation of the constancy of the time it took for planets to revolve, von Guericke concluded that space is also a vacuum without friction. He also conducted experiments on the elasticity of air, as well as the relation of air pressure and altitude. Combined with Blaise Pascal’s discovery of the link between atmospheric pressure and weather, von Guericke proposed meteorological stations to gather data to forecast the weather. Other discoveries he is credited with include the magnetization of iron, the invention of a static electricity generator, and the observation of colored shadows. -Mira Lamb 2018 References “Guericke, Otto Von,” accessed April 14, 2017. https://www.accessscience.com:443/content/ guericke-otto-von/m0091124. Marquardt, Niels. “Introduction to the principles of vacuum phsyics,” last modified November 22, 2016. https://cds.cern.ch/record/582156.