Christiaan Huygens established a wave theory of light in 1678. Why do you think that he waited until 1690 befo?
Probably because he wanted to make sure he was right? That is supposing he published it at his leisure. Remember, Darwin had to rush his publication of the Theory of Evolution because a fellow scientist had come to the same conclusions as him, albeit without the same level of research. I cannot recall the chaps name but I do believe he wanted to publish his theory to gain funding to further research it. Darwin had to rush his through to rubber stamp the idea as his. Perhaps Huygens had no such competition and could afford to wait until he was absolutely certain before announcing his theory? Or perhaps, whilst he was refining it some young upstart threatened to rock his boat and maybe he just put it out there for the World to see? I know nothing about this, I must admit, and have done no research! But I do know about Darwin and am just applying the same (sort of) course of events to Huygens work!
