Smoke signals? 100 years is approximately the amount of time between the telephone and the internet. The telegraph was around for about 50 years before that. Science has done well, but it's not like the twentieth century magically emerged straight from the stone age.
Just to push it back a bit further, revolutionary France and particularly Napoleonic France established a country-wide system of mechanical telegraph stations. They especially wanted it to warn of British naval attacks, but also for any military news.
It worked pretty well, transmitting, for example, a distance of about 200km (125mi) in about 9 minutes. The Brits would sail up and down the coast and fire on stations when they were feeling bored and mischievous.
Interestingly, Hooke (Newton's compatriot) proposed a similar system a couple of hundred years earlier, but the British military chiefs displayed their usual insight and did not take it up.
