Hauksbee sphere
In 1705, Francis Hauksbee put a small amount of mercury inside a glass bubble under a vacuum (enabled by Boyle’s invention) and rotated the glass sphere as fast as his belt-and-handle apparatus allowed him to. When doing so, he noticed a purple glow inside the rotating glass whenever his hand was placed near it. Hauksbee later lost interest in these “fine appearances” (as he called them) but his invention made him the first person to see the effects of electricity in vacuum. This was a giant leap for mankind. Since the days of ancient Greece we had only looked at sparks from static electricity as mere curiosity and amusement.
Source: 1. Hauksbee, F. Physico-Mechanical Experiments on Various Subjects: Containing an Account of Several Surprizing Phaenomena Touching Light and Electricity, Producible on the Attrition of Bodies. (Printed by R. Brugis, London, 1709).
Public Domain
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Full disclosure, I may occasionally borrow a sentence from Will Durant's Story of Civilization. I absolutely love that collection!