The Weight of the Human Soul (21 Grams)

I am linking to this article from the NY Times from about 100 years ago. I had always wondered what the phrase "21 grams" meant. Fooling around on Google, I did a quick search and was immediately struck by what I found: namely, that 21 grams is believed to be the weight of the human soul. I traced this odd little piece of info to its roots, and offer them here, in this reprint.