2. We want a bell upstairs to make a single stroke whenever the kitchen bell is rung from the front door.
3. We want a floor push under the dining-room table which will cause the kitchen bell to ring a single stroke.
4. We want a push button in the dining-room which will cause both bells to clatter and call people from their beds, from the piazza, the lawn, etc., to their meals.
This equipment needs only one battery of two dry cells, two bells, three push buttons and about two hundred feet of wire. It should cost less than five dollars.
The boys drew many plans and tried many schemes and at last determined upon the plan shown in [Fig. 173].
Fig. 173
P is the floor push under the dining-room table. When the circuit is closed at this point the current leaves the battery from the carbon pole c, passes up and around the magnets of the kitchen bell and back to the zinc pole of the battery z by way of the push button P. All other circuits are open.