Gauss' law of the arithmetic mean

Gauss' law of the arithmetic mean

[′gau̇s ‚lȯ əvthə ‚a·rith¦med·ik ′mēn]
(mathematics)
The law that a harmonic function can attain its maximum value only on the boundary of its domain of definition, unless it is a constant.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.