XVIII Electric Bell Outfit for the Cottage
The boys asked me what arrangement of electric bells we needed at the cottage and so I gave them this problem to work out by themselves:
1. We want a bell in the kitchen to be rung by a push button at the front door. But there are times when no one is in the kitchen and hence,
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.
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.
P´ is the push button at the front door. When the circuit is closed at this point the current leaves the battery at c, passes up to the right-hand binding post of the kitchen bell and divides, part going through each bell. The portion of the current which goes through the kitchen bell passes around the magnets and through the armature to the left-hand binding post before it can find a path back to the battery. Hence, the kitchen bell clatters. The portion of the current which passes to the upper bell goes around its magnets and finds a path back from the middle binding post to the battery by way of P´. Hence the bell upstairs rings with a single stroke.
P´´ is a push button situated upon the wall by the side of the door which leads from the dining-room to the kitchen. When the circuit is closed at this point, the current leaves the battery at c, passes up to the right-hand binding post of the kitchen bell and divides, part of it going through each bell. The portion which goes through the kitchen bell passes around its magnets and through its armature to the left-hand binding post, then up to the middle binding post of the upper bell, through its armature to its left-hand binding post and back to the battery by way of the push button P´´. The other portion of the current passes directly up to the right-hand binding post of the upper bell, around its magnets, and through its armature to its left-hand binding post, thence back to the battery by way of the push button P´´. Hence, both bells clatter and keep time with each other. The upper bell will ring independently of the lower bell, but the lower bell is dependent upon the upper one to open and close its circuit, somewhat as a relay.
Soon after the cottage had been equipped with electric bells I went to the mill one day and found a push button at the door. Upon going in I was curious to examine the electric bell outfit of that place and found what is illustrated in Fig. 174.
A switch, S, had been attached to the bell. The boys said that when they felt well they kept the switch upon the left-hand point and the bell rang as a clatter bell. When they felt a little sick they put the switch upon the middle point and the bell rang with a single stroke, but when they felt very sick they put the switch upon the dead point and the bell did not ring at all.