Theory Embodied in Instrument Design
The electric machine evolved out of the air pump at the turn of the eighteenth century. When a glass air pump receiver was rubbed, it glowed within, it attracted and repulsed small bits of string, depending on how much air was left in the receiver. These phenomena were ascribed to electrical matter ecited by the rubbing and pushed inside or outside the glass by air pressure. Consequently, the first electric machines were designed with hollow glass spheres or cylinders rubbed by a cushion. After scholars discovered that air pressure had no role in electrical attraction or repulsion, the fragile, hollow spheres were replaced with solid glass plates.
Instruments can be theory-laden.
- (From the information plate by the Globe Electric Machine at the Collection of Historical Scientific Instruments at Harvard)↵