Description: Vacuum hemispheres.

Caption: In fact it is the pressure of the air which keeps the hemispheres together and not the vacuum, which exerts no force. When the air is pumped out of them, the spheres are almost impossible to separate. In fact the iron they are made of would fail before the force applied could separate them.

Introduction: This apparatus, made by J.J. Griffin & Sons at London, in second half of the 19th century, demonstrates the power of the pressure of the atmosphere. the hemispheres were invented, in about 1663, by Otto von Guericke (1602-1686) to demonstrate, or so he thought, the power of an improved vacuum pump, invented by him in 1650.

Background: In 1663 Guericke travelled to Berlin to demonstrate his experiment with the Magdeburg hemispheres to the German Elector Friedrich Wilhelm. He used horses to try to pull them apart. The power of atmospheric pressure can also be demonstrated by heating an empty screw capped metal can (without the cap) and then removing the can from the heat and then quickly fitting the cap. As the can cools it will collapse.

Historical Context: Design - When: circa 1663 - Where: Magdeburg, Saxony (Prussia), Germany - Who: Guerick, Otto von (1602-1686)

Historical Context: Manufacture - When: circa 1900 - Where: London, England - Who: John J. Griffin & Sons Ltd

Historical Context: Use in lecture demonstrations - Who: Department of Natural Philosophy now called the Department of Physics and Astronomy, Glasgow University

Historical Context: Used in lecture demonstrations in the Department of Natural Philosophy now called the Department of Physics and Astronomy - When: circa 1900-1957 - Where: Natural Philosophy Lecture Theatre, Gilbert Scott Building, University of Glasgow, University Avenue, Glasgow, Scotland

Historical Context: Event - "Lord Kelvin: A life in science" exhibition, Hunterian Museum, University of Glasgow. Object on display in this exhibition.