| Dynamo | Battery | Motors | |||
| 36 | 27 | 27 | 20 | 20 | 15 |
| 15 | 12 | 12 | 9 | 9 | 7 |
| 7 | 5 | 5 | 4 | 4 | 3 |
| 3 | 2 | 2 | 1 | 1 | .8 |
| .8 | .6 | .6 | .48 | .48 | .36 |
| .36 | .27 | .27 | .20 | .20 | .15 |
| .15 | .12 | .12 | .09 | .09 | .07 |
| .07 | .05 | .05 | .04 | .04 | .03 |
| .03 | .02 | .02 | .01 | .01 | .003 |
It is evident that while our energy would dwindle continually we should never quite come out of the little end of the horn, since any number may diminish by 20 per cent. of itself indefinitely.
"Let us get at something practical," said Erg. "How are we going to furnish electricity to the cottage when the dynamo is not running? If we put a storage battery at the cottage, how are we going to store it having nothing but alternating current up there; and if we attempt to transmit current from our central station battery, how are we going to get along with the drop in the voltage?"
"I'll tell you how to do that," said Dyne. "They want 20 amperes and the line offers 4 ohms of resistance. That means a drop of 80 volts. We have simply to provide a subsidiary battery of 48 cells, which we may throw in series with our 57 cells when we supply electricity to the cottage, and then they will have the right voltage for use out there."
"Yes," said Erg, as he rolled over, "they will have the right voltage when they use 20 amperes, but what will happen if they simply turn on one lamp. The drop in voltage then will be (.5 amperes × 4 ohms =) 2 volts; 105 cells at 1.8 volts a cell will send out there 189 volts minus the drop of 2 volts, leaving 187 volts upon a lamp adapted to 110 volts, and it will immediately burn out. The same thing would happen to any single piece of apparatus if the current was turned upon it alone. The only thing they could do if they wanted to light a lamp, say in the middle of the night to take a dose of medicine, would be to start up all together, all their lamps, sewing machine, wringer, dishwasher, fireless cooker, vacuum cleaner, etc., etc., to keep down the voltage so that one lamp would not burn out."
"I have read," said Ernest, "that they use rectifiers, which convert the alternating into direct current, for storing batteries. These are much used over the country. Electric automobiles run by storage batteries, and in the great majority of communities there is no other electric current than the alternating. So they would be helpless without the rectifier. We should then get another battery of fifty-five cells for the cottage and keep it stored by using a rectifier with our alternating current.
"But all their equipment up there," said Ernest, "is adapted to the alternating current. Of what use would a direct current be to them?"
"Well," said Harold, "it is all the same whether you have alternating or direct current on lamps, cooking apparatus, etc., and I have understood that they have motors which run on both alternating and direct currents. If so, that would fix them up all right."
The boys now turned to me for the first time to inquire whether motors could be obtained which would run on both alternating and direct current, and I replied that small motors for running sewing machines, vacuum cleaners, etc., were made which would serve us, perhaps not economically, but as they were the only solution to our problem we could get along with them.