by William Gilbert, On the Magnet — Book II. Chap. 19… (1900)
“ Coitio verò non fortior.—This heading to chap. xix., taken with the seven lines that follow, and the contrast drawn between unitio and coitio, throw much light on the fundamental sense attached by Gilbert to the term coitio. It is here clearly used in the sense of mutual tendency toward union. Note also the contrasted use in chap. xx. of the verbs cohære and adhære. Adhærence connotes a one-sided force (an impossibility in physics) , cohærence a mutual force. ”
