A star cluster must, of course, give a similar spectrum, resulting from the superposition of the spectra of the single stars in the cluster.
"The Story of the Heavens"
Robert Stawell Ball
In this early stage proofs should not be given with pedantic fullness; definitely fallacious methods, such as that of superposition, should be rigidly excluded from the first, but where, without such methods, the proof would be very difficult, the result should be rendered acceptable by arguments and illustrations which are explicitly contrasted with demonstrations.
"Mysticism and Logic and Other Essays"
Bertrand Russell
Three principal Tests of relative Age: superposition, Mineral Character, and Fossils.
"The Student's Elements of Geology"
Sir Charles Lyell