"A characteristic of older folksongs, in most cases, is that we don't know their composers or authors. Older folksongs were written often with no commercial purpose in mind. They were passed down by word of mouth, from generation to generation."

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For in 1900 all electromagnetic radiation of longer wavelengths was already known at least to the extent that one could not seek in it the more striking characteristics of X-rays such as, for example, the strong penetrating power.

— Max von Laue