Is that the one that monitors the circuit in my body?
"Tangle Hold"
F. L. Wallace
He intends to provide for his own living by working at his trade, and he will take for instruction about four boys at a time, and as soon as he has brought them forward enough, set them as monitors over others.
"Memoir and Diary of John Yeardley, Minister of the Gospel"
John Yeardley
Admiral Sampson's armored ships numbered seven to Cervera's four, a proportion not dissimilar; but those seven were all the armored ships, save monitors, worthless for such purpose, that the United States owned, or would own for some months yet to come.
"Lessons of the war with Spain and other articles"
Alfred T. Mahan