SOLAR AND ARTIFICIAL LIGHT COMPARED.
The most intensely ignited solid (produced by the flame of Lieutenant Drummond’s oxy-hydrogen lamp directed against a surface of chalk) appears only as black spots on the disc of the sun, when held between it and the eye; or in other words, Drummond’s light is to the light of the sun’s disc as 1 to 146. Hence we are doubly struck by the felicity with which Galileo, as early as 1612, by a series of conclusions on the smallness of the distance from the sun at which the disc of Venus was no longer visible to the naked eye, arrived at the result that the blackest nucleus of the sun’s spots was more luminous than the brightest portions of the full moon. (See “The Sun’s Light compared with Terrestrial Lights,” in Things not generally Known, pp. 4, 5.)