Marci Shimoff, Carol Kline, Marianne Williamson (2012). “Love For No Reason: 7 Steps to Creating a Life of Unconditional Love”, p.49, Simon and Schuster
Quoted in Evan Esar, The Dictionary of Humorous Quotations (1949). Usually attributed to Dewar, but it should be noted that the line "mind like parachute - only function when open!" appears in the 1936 film Charlie Chan at the Circus (screenplay by Robert Ellis and Helen Logan).