Who wrote the quote Your mind is like a parachute?

According to several sources on the internet, the quote is attributed to Frank Zappa.

However, in the 1936 movie "Charlie Chan at the Circus," Charlie Chan says, "Mind, like parachute, only function when open," slightly less than an hour into the movie. Most web sites credit Sir Thomas Robert Dewar, who died in 1930, but his authorship has been questioned. At least one website attributes it to the Dalai Lama.

Here's an equally good quote from Will Rogers:

You know you've got to exercise your brain just like your muscles. The quote originated in Scotland by Sir Thomas Robert Dewar (1864 - 1930)