A similar more famous experiment that didn’t involve explosions was possibly conducted or at the very least proposed by Galileo Galilei just under a decade later in 1638. Galileo, like Beeckman also suspected that the speed of light wasn’t infinite and made passing references to an experiment involving lanterns in some of his work. His experiment (if he ever conducted it at all), involved placing two lanterns a mile apart and trying to see if there was any noticeable lag between the two; the results were inconclusive. The only thing Galileo could surmise was that if light wasn’t infinite, it was fast and that experiments on such a small scale were destined to fail.
It wasn’t until Danish Astronomer, Ole Römer entered the fray that measurements of the speed of light got serious. In an experiment that made Galileo flashing lanterns on a hill look like a primary school science fair project, Römer determined that, lacking lasers and explosions, an experiment should always involve outer space. Thus, he based his observations on the movement of planets themselves, announcing his groundbreaking results on August 22, 1676.
Specifically, while studying one of Jupiter’s moons, Römer noticed that the time between eclipses would vary throughout the year (based on whether the Earth was moving towards Jupiter or away from it). Curious about this, Römer began taking careful notes about the time I0 (the moon he was observing) would come into view and how it correlated to the time it was usually expected. After a while, Römer noticed that as the Earth orbited the sun and in turn got further away from Jupiter, the time Io would come into view would lag behind the expected time written down in his notes. Römer (correctly) theorized that this was because the light reflected from Io wasn’t traveling instantaneously.
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