These motors were all adapted to the 110-volt direct current and the battery contained fifty-seven cells, each cell being rated a little under two volts. The boys frequently discussed possible combinations in this system. I spent a great deal of time loafing around among them in a comatose condition, and they talked quite as freely when I was around as when they were alone among themselves. One day I heard Dyne say, "Suppose we should store in a reservoir the water which comes down the penstock during a day and store all the electricity it will generate in a day in a storage battery, then at night let the battery run the dynamo backward as a motor, and that turn the water-wheel backward as a rotary pump, we should have the water in the upper reservoir to begin work with the next morning and the problem of perpetual motion would be solved. "Aw, why do you want to do all that," said Erg, "when nature is doing it for us?" Ernest said he had a better scheme than that. He would turn the battery current on to all the motors in the room and they would run the counter shafts forward and the counter shafts would run the dynamo forward and the dynamo would charge the battery, and so you could keep up the motion perpetually if you wanted to. "Get out your pencils," said Harold, as he took down a copy of Houston and Kennelly. "Let us see how we would come out if we tried Dyne's proposition for, say, twenty hours, storing the energy from the falling water for ten hours in the battery and then using this energy during the next ten hours for re-storing the water in the upper pond. We will say that the water-wheel furnishes eight horse-power for ten hours--eighty horse-power hours." I notice it is stated in this book that small dynamos are usually unable to deliver more than 75 per cent. of the energy impressed upon them, and storage batteries and motors deliver about 80 per cent. of the energy impressed upon them. The accounts would, therefore, stand as follows: _Dynamo_ _Horse-power Hours_ _Dr._ _Cr._ To energy impressed by water-wheel 80 By energy delivered to storage battery 60 By loss in heat 20 --------- 80 80 (Assuming that the battery was able to receive all the dynamo could give.) STORAGE BATTERY ACCOUNT To energy impressed by dynamo 60 By energy delivered back to dynamo running as motor 48 By loss in heat 12 --------- 60 60