A historical is a mixture of fact and fiction. The writer's task is to ensure the accuracy of historical facts so the reader believes he or she is a part of the story.

The best example of this is the 1980 movie, Somewhere in Time. Here's the wikipedia blurb on this production:
 
Christopher Reeve plays Richard Collier, a playwright who becomes smitten by a photograph of a young woman at the Grand Hotel. Through self-hypnosis, he travels back in time to the year 1912 to find love with actress Elise McKenna (portrayed by Jane Seymour).

The assumption is that time travel is possible if he believes it. In his hotel room, Richard removes or hides everything that doesn't fit 1912.  With an early 20th century hair cut and dressed in period clothing, he lies down on the bed and 'thinks' himself back in time. As long as he doesn't encounter anything from his birth era, he stays in the past.

*SPOILER ALERT
During a crucial point in the film, Collier puts his hand in his trousers pocket and pulls out a 1979 Lincoln penny. Suddenly, he remembers everything. With Elise crying out his name, he comes back to modern times.

No, I'm not going to tell you how it ends. You can rent the movie or read the wikipedia article.

My point in bringing this movie to your attention is to show you what I'm trying to do in my research... remove everything that doesn't belong in the time I've set for my story so that you, as the reader, believes you're right there where it's happening.

To that effect, the pages refered in the right side bar will show you some of the research I've undertaken to ensure the historical accuracy of my stories.