How was V. Herschel able to figure out the structure of the Milky Way?

William Herschel, whose list of scientific merits is enormous, was the first to try to determine the shape and size of our huge star system, called the Galaxy – from the Greek “galatios”, which means “milky”. The task was not easy and fraught with mistakes, since W. Herschel had no idea about the interstellar absorbing matter. In the end, he got a structure like a thick lens with heavily jagged edges, with the Sun almost exactly in the center of the Galaxy. Knowing full well that this is not so, let us refrain from criticizing the great astronomer. Perhaps, at the current level of knowledge, it was impossible to achieve a greater result.
The conjecture that the star system of the Milky Way may be just one of countless such systems was put forward in 1734 by the Swedish philosopher Emmanuel Swedenborg. W. Herschel also suggested that at least some light nebulae, interpreted as relatively close to us protostellar clouds, in fact, may be very distant star clusters – galaxies in which it is impossible to consider the stars separately due to the very great distance before them. At the same time, astronomical observations of the planetary nebula NGC 1514, carried out by Herschel in 1785, made it possible to see in its center a single star surrounded on all sides by a mysterious nebula resembling scattered clouds. Thus, the existence of genuine nebulae within the boundaries of our Galaxy, the Milky Way, was confirmed. In the nebula, like distant star systems, after that it was hard to believe.