Click to embiggenFrom the Library of Congress, we find a diagram of astrophysics equipment from the 19th century. It’s not a telescope. It’s a device designed to disprove the existence of the luminiferous ether, the stuff that we once thought filled outer space rather than the endless void we now know we’re all suspended in. The idea was that light needed something to travel through, some kind of medium, just like sound needs to travel through air (or water, or solid objects). The interferometer was designed to measure the speed of light in two different directions. Since we’re on a planet moving super-fast in one direction through what should have been this ether substance, the light should have experienced some kind of drag in one direction or another. It didn’t.
The full name of this piece is “Diagram of interferometer and four mirrors mounted on stone floating in mercury, which disproved existence of luminiferous ether and its role in the transmission of electromagnetic waves; with surrounding text,” and it first appeared in the December 1887 issue of Philosophical magazine, in the article, “On the relative motion of the earth and the luminous aether,” by Albert A. Michelson and Edward W. Morley.