What is the author's tone in Mere Christianity by C. S. Lewis?

Lewis' tone varies from calm and assured to strident. He injects what might have come off over the radio as humor, but in the printed version of the scripts, the humor might be too dry for American readers to catch. Some of the words Lewis uses have special meanings in British English, such as "ell" for the length of 45 inches. Lewis uses the term in this context: Give them an inch and they want an ell. Overall the book's tone is appealing as each short script, written to cover 10 minutes of air time, appeals to the intellect more than the emotions.

At times the tone becomes nearly monotonous. The author is usually quick to bring in something to wake the reader up, or in the case of the radio version, recapture attention.