XIX Using Electricity to Aid the Memory
For the sparking equipment of the motor boat we use dry cells which have an internal resistance of not more than.06 ohm. They will, when short circuited through the ammeter for only an instant, give 25 amperes.
(1.5 volt)/(.06 ohm) = 25 amperes
When we allow for a slight resistance in the ammeter itself, and for the drop in voltage, we see that the internal resistance of a cell must be even less than.06 ohm.
After being used about two months upon the motor boat these cells develop more internal resistance, and they will then show not more than six to ten amperes when short circuited through an ammeter. They are then not reliable for ignition of the engine, but are quite as good as ever for bell-ringing, and often continue so for more than a year. The result is that we always have more partly run-down dry cells than we can use. Seeing them about has stimulated the boys to devise ways for using them.
The housekeeper is distracted by carrying on so many cooking processes at one time. She forgets the eggs, and lets them boil five minutes instead of three because the coffee must percolate twelve minutes, and she lets the coffee percolate twenty instead of twelve minutes because the biscuit must bake twenty minutes, and the biscuit are forgotten because the pies must come out in thirty minutes, and the cake in forty minutes. All this worries the cook. Harold is a sympathetic boy and enters into the troubles of others. I had at one time shown him how to bore a hole in a glass plate in five or ten minutes by using a round file wet with water. One day he presented the kitchen with a clock, intended to relieve the burdened memory of the cook. This is represented in Fig. 175.
An ordinary kitchen clock had a hole bored through the glass which covers its face. This glass is easily moved around in its metal rim, bringing the hole over any desired minute upon the face. One wire of the battery is attached to a leg of the clock, the other goes to a bell, and then the wire from the bell is poked through this hole. When the minute hand reaches that point the electric current is closed through the metal of the clock, and the bell rings warning that the eggs, coffee or what not are done.
We each urged that our memories should share in the vacation, and applied for one of these outfits. I took one of the clocks and cut back the minute hand so as to make it shorter than the hour hand, and then had the hole in the glass made so that the hour hand should close the electric circuit. This was kept at my study table and reminded me of my appointments. Some used these clocks to alarm themselves in the morning when they slept overtime.
Another reminder is shown in Fig. 176. C is a float which rises and falls with the water in our house tank. A cord running over two pulleys connects this with a weight, d, hanging in front of a scale upon the wall of the kitchen. This indicates how much water there is at any time in the tank, which is situated in the garret. The boys arranged a bell and battery so that when the tank is nearly empty the weight d will pull upward a spring, a, and make it close the circuit through the bell to warn that water must be pumped. When the tank is nearly full the weight d pushes down the spring b and rings the bell again.
Harold said that yeast cakes were the heaviest tax upon our memories. If some one started for the village store, before he got out of hearing, a call would come after him, “I forgot the yeast cake. Please put that on the list.” When one returned from the village store with numerous packages, he would generally hear, “My yeast cake was forgotten.” We tried all sorts of schemes to get rid of this yeast-cake nuisance, and finally adopted Harold’s “curled bread” project.
We had built a brick oven out back of the house for experimental purposes. Harold proposed that the boys bake a month’s supply of bread at a time, and, when it was a day or two old, cut it all into thin slices and let it dry. These slices curled up as they dried and were known as “curled bread.” A flour barrel was filled with it each month. It kept perfectly any length of time. The family voted it to be better than crackers and better than fresh breadstuff of any kind.
Harold’s suggestion regarding yeast cakes worked so well and was such a relief to our memories that I proposed he next attack the problem of the often forgotten salt in cooking.