Although the equivalence of these words is clear, for example, in Ohm's work of 1826, the context in which Kette is sometimes used in 1820 and 1821 indicates that the concept of a "circuit," in the sense of the wiring external to the source of electricity, has not been established.
"The Earliest Electromagnetic Instruments"
Robert A. Chipman
"Is" can denote a wide variety of ideas, from that of personal identity, as when I see that yonder distant figure is my brother; to that of equivalence, as when a stamped and signed piece of thin paper called a bank-note is five pounds of gold; or to that of mere representation, as when another piece of paper, or a sheet of canvas, duly lined and coloured by the artist to show the semblance of a human face, is the King, or is my father; or to that of result and effect, as when we say that knowledge is power, or that seeing is believing.
"Messages from the Epistle to the Hebrews"
Handley C.G. Moule
When energy is transformed there is an equivalence between the new form and the old.
"Edward Caldwell Moore Outline of the History of Christian Thought Since Kant"
Edward Moore