Benjamin Franklin, William-Temple Franklin (1818). “Memoirs of the Life and Writings of (the Same), Continued to the Time of His Death by William Temple Franklin. - London, H. Colburn 1818”, p.249
Bhante Henepola Gunaratana (2010). “Beyond Mindfulness in Plain English: An Introductory Guide to Deeper States of Meditation”, p.43, ReadHowYouWant.com