The Ether. --One cannot conceive of motion taking place in a void, for there would be nothing to move. Now heat, light, and other manifestations of energy come to the earth from the sun, and it is assumed that interstellar space must be filled by a transmitting medium, to which the name of ether has been given. It is not known whether this ether is continuous or molecular in structure, but it is believed that it penetrates all bodies and fills up the space between their molecules. One can only speculate as to its density and rigidity.
Solar Radiation. --The sun, with a diameter of 865,000 miles, which would fill the space occupied by our earth and also that inclosed by the orbit of our moon and extend 200,000 miles beyond, is continuously sending out an enormous quantity of radiant energy. Only a minute part of this encounters any planet and is absorbed, and thereby transmuted into other forms of energy. The greater part passes on indefinitely into space, becoming less and less intense with increasing distance. The amount received by the earth is but 1/2200000000 part of the whole, yet in one minute it would heat 37,000,000,000 tons of water from the freezing to the boiling temperature, if 2.6 be the solar constant and 2,000 pounds the ton.
INSOLATION is the term applied to the solar radiation received by terrestrial or planetary objects. Formerly this word meant exposure to the sun's rays, and it is still occasionally used in that sense.
The change in temperature, in electrical state, in chemical composition, or any other effect produced on an object by exposure to sunshine, varies widely in nature and extent with different objects. In the case of black bodies, or perfect absorbers, essentially the entire effect is a change in temperature--a change that is measurable and directly proportional to the total incident energy.