The Wednesday quotation, Part V: Spinoza on the union of bodies.

When a number of bodies of the same or different size are driven so together that they remain united one with the other, or if they are moved by the same or different rapidity so that they communicate their motions one to the other in a certain ratio, those bodies are called reciprocally united bodies (corpora invicem unita), and we say that they all form one body or individual, which is distinguished from the rest by this union of bodies. (Ethics 50)