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     When the set is in operation, we know that there is a current (electricity) flowing in wires A & B. We know that current is but the movement of electrons. Now how are these electrons moving--in a steady stream? No, because then the current would be direct current.
     We can place in one of these wires (as shown in Fig. 14) an electric eye that can "see" the electrons as they move through the wire and actually measure them. This device is the "oscillograph." Its eye is so quick that it can detect a difference in the number of electrons flowing every thousandth of a second. Let us put it to work for us. This is what it will tell us--and for convenience, the facts have been arranged in tabular form.
TABLE NO. 9

Time in Seconds	Current in Amperes	Direction
.00126	5.	Right
.00294	8.7	"
.0042	10.0	"
.0056	8.7	"
.0069	5.	"
.0083	0.	"
.0097	5.	Left
.01	8.7	"
.0125	10.	" etc.

     Observe Table No. 9 carefully--notice that the electrons flow first in one direction, increasing in numbers to a maximum and then decreasing until they actually stop moving entirely. Then they flow in the other direction, increasing in numbers to a maximum and then decreasing until they stop entirely and then they flow in the first direction again.
     By this time you could plot these facts in graph form for yourself but just to show you how the curve looks, Fig. 15, is included. Notice that the curve is drawn on a horizontal line which is the zero line or "no movement" line. The horizontal divisions represent time intervals and the divisions on the vertical line represent current flow in amperes. The portion of the curve above the zero line represents current flow in one direction, below the line, current flow in the opposite direction.
     Scientific investigation has advanced with such strides in recent years that today it is actually possible to photograph an

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Content	©1931, National Radio Institute
Webpage	©1997, Nostalgia Air
Transcriber	Richard Lancaster