Brass Magdeburg hemisphere apparatus on a wooden stand, made by George Adams, Fleet Street, London, 1762.
In the mid-seventeenth century Otto von Guericke used an air pump to remove the air from between two large close-fitting hemispheres. Teams of horses could not separate them. A scaled down version carried out with air pumps became a standard demonstration. If the air was removed from between the hemispheres, a weight of 40 lb was required to separate them. However, if they were placed in a bell jar and the air was removed, they fell apart. These hemispheres were made by George Adams for King George III.