Sentence:  The experiments of Romagnosi and others have already been noted but no one had determined the cause and effect <WSD>relationship</WSD> between these two primary forces . 
Meaning of the word marked with <WSD> tags:  a relation between people; (`relationship' is often used where `relation' would serve, as in `the relationship between inflation and unemployment', but the preferred usage of `relationship' is for human relations or states of relatedness)