During a basic lecture about system design the transfer function H(s) was discussed. The question was raised why the letter 'H' is used for this... Sounds weird, but I did start to think about it... Indeed in many books and publications the letter H (besides sometimes G(ain)) is used to describe the transfer function. I googled around but I didn't come further than the fact that H(s) is the Laplace transform of the impulse response, denoted by h(t). Lovely explanation, but of course it moves the problem to where 'h' comes from in the impulse response... Maybe I am looking over something extremely trivial, but I can't seem to get around it. Anybody any idea what the (historical) reason for this mysterious 'H' is?