Photoacoustic effect a rotating slotted wheel. He noticed that the resulting acoustic signal was dependent on the type of the material and correctly reasoned that the effect was caused by the absorbed light energy, which subsequently heats the sample. Later Bell showed that materials exposed to the non-visible (ultra-violet and infra-red) portions of the solar spectrum can also produce sounds and invented a device, which he called "spectrophone", to apply this effect for spectral identification of materials. Bell himself and later John Tyndall and Wilhelm Röntgen extended these experiments, demonstrating the same effect in liquids and gases. However, the results were too
Ultraviolet (Light My Way) singing the repeated "baby"s, one of the most heavily used clichés in pop songs and one that he had avoided up to that point in his songwriting; Flood later commented that "he got away with it alright." Although the song is ostensibly about love and dependency, like many U2 songs, it also lends itself to religious interpretations. Listeners have heard an allusion to the Book of Job and its tale of God serving as a lamp upon Job's head walking through the darkness. Robyn Brothers suggests that ultraviolet light is "a metaphor for a divine force both unseen to the