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An example of radiant heat. "Radiant heat is transmitted in a vacuum as well as air." A thermometer is on top of the glass flask. The flask neck is narrowed by the blowpipe. The flask is attached to an air pump with which a vacuum is produced in the interior.

Radiant Heat

An example of radiant heat. "Radiant heat is transmitted in a vacuum as well as air." A thermometer…

"The radiation of light, or the intensity of light is inversely proportional to the square of the distance from the light source." —Croft 1917

Light Intensity

"The radiation of light, or the intensity of light is inversely proportional to the square of the distance…

"If a pair of concave mirrors be set facing each other, as shown in figure 7, and a source of heat be placed in the focus of one, a thermometer in the focus of the other will quickly show a rise in temperature though the mirrors are many feet apart." Louis Derr, 1911

A Pair of Concave Mirrors Set Facing Each Other

"If a pair of concave mirrors be set facing each other, as shown in figure 7, and a source of heat be…

"Stevenson's louvre-boarded box for the thermometers, which is now very widely used for temperature observations. The box is made of wood, and louvred all round so as to protect the thermometers inside from radiation, and at the same time secure as free a circulation of air as is consistent with a satisfactory protection from radiation. The box is painted white, both inside and outside, and screwed to four stout wooden posts, also painted white, firmly fixed in the ground. The posts are of such a length that when the thermometers are hung in position the bulbs of the minimum thermometer and hygrometer are exactly at the same height of 4 feet above the ground, the maximum thermometer being hung immediately above the minimum thermometer." —The Encyclopedia Britannica, 1903

Thermometer Box

"Stevenson's louvre-boarded box for the thermometers, which is now very widely used for temperature…