The scientist who measured the charge on an electron was Robert Millikan. He conducted the famous oil drop experiment in 1909.

Here's how the experiment worked:

* Oil droplets were sprayed into a chamber.

* The droplets were charged by friction with the nozzle.

* Electric fields were applied to the chamber, allowing Millikan to control the droplets' motion.

* By observing the droplets' movement, Millikan could calculate the charge on each droplet.

Millikan found that the charges were always multiples of a specific value, which he determined to be the charge of a single electron. His experiment provided strong evidence for the existence of the electron and its quantized charge.