Note 12 — Chapter III · ON ELECTRIC BELLS AND OTHER SIGNALLING APPLIANCES.
Reading edition
A "push," of which several forms will hereafter be described and figured, consists essentially in a spring carrying a stud, standing directly over, but not touching, another stud, fixed to a base. The lower stud is connected to one terminal of battery, the spring is connected to the bell. When the spring is pressed down, the two studs come into contact, the current flows, and the bell rings.