“What one man calls God, another calls the laws of physics.”

Opening lines, p. 104
Variant translations:
What is God-given is called nature; to follow nature is called Tao (the Way); to cultivate the Way is called culture.
As translated by Lin Yutang in The Importance of Living (1937), p. 143
What is God-given is called human nature.
To fulfill that nature is called the moral law (Tao).
The cultivation of the moral law is called culture.
As translated by Lin Yutang in From Pagan to Christian (1959), p. 85
The Doctrine of the Mean

Address to the Society for Psychical Research (1897)
Context: These rays, as generated in the vacuum tube, are not homogeneous, but consist of bundles of different wave-lengths, analogous to what would be differences of colour could we see them as light. Some pass easily through flesh, but are partially arrested by bone, while others pass with almost equal facility through bone and flesh.
It seems to me that in these rays we may have a possible mode of transmitting intelligence which, with a few reasonable postulates, may supply a key to much that is obscure in psychical research. Let it be assumed that these rays, or rays even of higher frequency, can pass into the brain and act on some nervous center there. Let it be conceived that the brain contains a center which uses these rays as the vocal chords use sound vibrations (both being under the command of intelligence), and sends them out, with the velocity of light, to impinge on the receiving ganglion of another brain. In this way some, at least, of the phenomena of telepathy, and the transmission of intelligence from one sensitive to another through long distances, seem to come into the domain of law and can be grasped. A sensitive may be one who possesses the telepathic transmitting or receiving ganglion in an advanced state of development, or who, by constant practice, is rendered more sensitive to these high-frequency waves. Experience seems to show that the receiving and the transmitting ganglions are not equally developed; one may be active, while the other, like the pineal eye in man, may be only vestigial. By such an hypothesis no physical laws are violated; neither is it necessary to invoke what is commonly called the supernatural.

Adams as portrayed in the musical 1776 (1969); this has sometimes been cited as an actual quote of Adams.
Misattributed

The attraction of the earth
Atheist Central
2010-02-24
http://raycomfortfood.blogspot.com/2010/02/attraction-of-earth.html
2011-10-21

The Great Chain of Life (1956), Chapter 9 "The Vandal and the Sportsman" http://books.google.com/books?id=Ydc0cooCB6QC&lpg=PA146&q="when+a+man+wantonly+destroys+one+of+the+works+of+man+we+call+him+vandal+when+he+wantonly+destroys+one+of+the+works+of+god+we+call+him+sportsman"#v=onepage. Iowa City: University of Iowa Press, 2009, p. 148.

Quoted in "Leaping the Abyss" (April 2002) by Gregory Benford, in Reason Magazine http://reason.com/archives/2002/04/01/leaping-the-abyss/4

On tithing - "TB Joshua Returns Elderly Woman's Half-A-Million Naira Tithe" http://www.premiumtimesng.com/letter-to-the-editor/176233-t-b-joshua-returns-elderly-womans-half-a-million-naira-tithe176233.html Premium Times, Nigeria (February 4 2015)

Better than Good: Creating a Life You Can't Wait to Live (2007)

In "Gods", ADAM International Review, No. 299 (1962)