A speck of dust above our own globe is pulled down to the earth, though the winds may bear it up for a time. If the speck were placed within a measurable distance of the sun, the sun would pull it in. But there is something else the sun is doing besides pulling things to it. It is pouring out energy, radiating light. Only a two-thousand-millionth of this great out rush of energy falls on the earth, but, even so, the pressure of the sun’s light on the earth is equal to 75,000 tons.