It is curious to reflect, for example, upon the remarkable legend of the Philosopher's Stone, one of the oldest and most universal beliefs, the origin of which, however far back we penetrate into the records of the past, we do not probably trace its real source.
For example, some stars put out large amounts of energy in the infrared part of the spectrum, so that this can produce a different relative magnitude rating than using light energy from the middle of the spectrum.
