Complex sentence: They were first investigated by Jules-Henri Poincaré in the 1890s, and he noticed that the paths leading to and from any of these points would almost always settle, for a time, on the orbit around it.
Split into simpler sentences: They were first investigated by Jules-Henri Poincaré in the 1890s. He noticed that the paths leading to and from any of these points would almost always settle, for a time, on the orbit around it.