A Binary Search

Have you ever done a binary search? Yes, it's a computer term, but I bet you've done it without knowing what it is. I did one during FGS 2013 at the Allen County Public Library (ACPL) and thought I'd share the concept.

One of my ancestors was injured in a work accident in the Chicago area and I'd like to learn more about it. I've heard two different versions in family legends. Searching newspaper archives by name and location has not turned up an article.

In the 1900 census, Walter McFarlane was a "motorman", most likely on the streetcars. In 1910, he was a night watchman at a cemetery. His injury had left him brain-damaged and able to do only menial work. The period from 1900 to 1910 is a huge time span for searching Chicago newspapers.

The ACPL has Chicago city directories on microfilm. If they had been books, I would have looked at each one in order to see Walter's job. But it takes a lot longer to load film and then find the right page.

A binary search says to go to the middle of the span being searched. So I first checked 1905, which said watchman. I just eliminated half the years.

Split the difference between 1900 and 1905, I chose 1902. Motorman.
Split the difference between 1902 and 1905. I chose 1904. Motorman.

City directory information is gathered some time before publication. But I now know that the injury occurred sometime during or after the compilation of the 1904 directory and before the compilation of the 1905 directory.

I found that by looking at only three microfilms. Going in order through each one, I would have looked at five.

If you've done a binary search, you now know the name for it. If not, I hope you have a new idea that might apply to one of your research opportunities.