Spencer, H. (1880). The multiplication of effects. In H. Spencer, World's famous literature. First principles (pp. 362-386). Philadelphia, PA, US: David McKay Publisher.
http://dx.doi.org/10.1037/12424-025
To the cause of increasing complexity set forth in the last chapter, we have in this chapter to add another. Though secondary in order of time, it is scarcely secondary in order of importance. Even in the absence of the cause already assigned, it would necessitate a change from the homogeneous to the heterogeneous; and joined with it, it makes this change both more rapid and more involved. To come in sight of it, we have but to pursue a step further that conflict between force and matter already delineated. Let us do this. (PsycINFO Database Record (c) 2016 APA, all rights reserved)