Generally speaking we do not suppose them specifically different; but only attribute to them different relations, connections and durations. 戴维·休谟.人性论.
To produce all the requisite signals with a single pith-ball electrometer, it was necessary to vary the durations of each divergence, and to combine several to form a single symbol. 弗雷德里克·科利尔·贝克维尔.伟大的事实.