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.)