In today's Newsday (a Long Island, NY newspaper) there was an article about the 100th anniversary of arguably the most important invention of the 20th century. The article was a recollection of the inventor by his neice. In the second paragraph she recalls:

> "He was sitting there with a notepad and his ever-present
> slide rule," she says. "I asked, 'What are you doing out
> here, Uncle Willis?' He looked up and said, in all
> seriousness, 'Trying to figure out the size of a drop of
> water.'"

For the whole article:

http://www.newsday.com/mynews/ny-p2top22777903jul09.story