This second measurement teaches us that a _certain quantity_ will pass out of the pipe in a _certain time_ if the pressure is steady, such quantity depending, of course, on the size or friction resistance of the pipe.
In electricity the volts of pressure act so as to force the quantity of current to _flow through the wires at a certain rate_ per second, and the rate at which it flows is measured in ampères. For instance, let us suppose that an electric lamp required a pressure of 100 volts and a current of one ampère to light it up, we should have to supply a current of electricity flowing at the rate of one ampère, acted upon by an electromotive force of 100 volts.
You will see, therefore, that while the volt does not represent any electricity, but only its pressure, the ampère represents the _rate of flow_ of the current itself.
You should remember that there are several words sometimes used in connection with the word "ampère"--for instance, we might say that a lamp required a "current" of one ampère or that a dynamo would give a "quantity" of 20 ampères.
_The Ohm._--You have learned that the _pressure_ would discharge the _quantity_ of water at a certain rate through the pipe. Now, suppose we were to fix _two_ discharge-pipes to the tank, the water would run away very much quicker, would it not? If we try to find a reason for this, we shall see that a pipe can only, at a given pressure, admit so much water through it at a time.
Therefore, you see, this pipe would present a certain amount of _resistance_ to the passage of the total quantity of water, and would only allow a limited quantity at once to go through. But, if we were to attach two or more pipes to the tank, or one large pipe, we should make it easier for the water to flow, and, therefore, the total amount of resistance to the passage of the water would be very much less, and the tank would quickly be emptied.
Now, as you already know, water has substance and weight and therefore occupies some space, but electricity has neither substance nor weight, and therefore cannot occupy any space; consequently, to carry electricity from one place to another we do not need to use a pipe, which is hollow, but we use a solid wire.