The rate of temperature change in soil and rock from the surface to the interior of the Earth: The geothermal gradient on the average is estimated to be an increase of about +10°C per kilometer.

The temperature difference between warmer surface waters of the ocean and colder deep waters, whereas the deep waters are about 20-50 degrees Fahrenheit colder that the surface waters: In principle, the ocean thermal gradient can be utilized with various types of ocean thermal energy conversion systems.

A solar pond that consists of three main layers; the top one is near ambient temperature and has low salt content, while the bottom one is very hot and salty and is lined with a dark-colored material.

The middle (gradient) zone acts as a transparent insulator, permitting sunlight to be trapped in the bottom layer (from which useful heat is withdrawn).

This middle layer, which increases in brine density with depth, counteracts the tendency of the warmer water below to rise to the surface and lose heat in the air.

1. The voltage per unit length along a resistor or other conductive path.
2. The electric field in a region, defined as the potential difference between two points divided by the distance between them.