How did William Herschel’s ideas about nebulae change after his 1790 observation?

Before his 1790 observation, William Herschel maintained that all nebulae were composed of stars. He argued that those he could not resolve into individual stars were simply distant "island universes"—vast systems of stars similar to our own galaxy—and he rejected the theory that a mysterious "luminous fluid" existed in space.12

However, on November 13, 1790, Herschel observed a nebula that he was forced to interpret as a central star surrounded by a cloud of luminous fluid, which directly contradicted his earlier hypothesis. Rather than abandoning his work, he adapted his theory to incorporate this new evidence. He concluded that the central star he observed was actually condensing out of the surrounding cloud due to the force of gravity. By 1811, he further expanded this cosmogony to describe the stages of stellar formation, tracing the process back to a time before stars had begun to form from the fluid.1