In 1867, Lord Kelvin imagined atoms as knots in the aether.
I had never heard of this before, and I find the idea absolutely delightful. As I understand it, the "knots" are stable vortices in the aether. It was popular from 1870 - 1890, and it blows my mind that only a few years later the electron was discovered (1897), and less than 50 years later (1938), the scanning electron microscope was invented! 1955 was when the atom was first imaged.