+--------------------+----+----+----+---+---+---+---+---+----+---+ |LENGTH OF CIRC., CM.|200 |180 |160 |140|120|100| 80| 60|200 | O | +--------------------+----+----+----+---+---+---+---+---+----+---+ |DEFLECTION; WEST |26° |28° | 30°| | | | | | 26°|67°| +--------------------+----+----+----+---+---+---+---+---+----+---+ |DEFLECTION; EAST |25° |27° | 30°| | | | | | 25°|67°| +--------------------+----+----+----+---+---+---+---+---+----+---+ | AVERAGE |25.5|27.5| 30 | | | | | |25.5|67 | +--------------------+----+----+----+---+---+---+---+---+----+---+ Fig. 97.] =316. Directions.= (A) With the circuit arranged as in Fig. 96, and with G V properly placed, take the reading of G V, the current passing through 200 cm. of No. 30 G-S W. Record your results in a diagram made like Fig. 97. The row of figures across the top shows the length of the circuit. The table is started with results from one experiment. Your results will probably be different from these. (B) Get the deflection with the current passing through 180 cm. of wire. To do this press a piece of copper (O, Fig. 96) upon the wire at the mark 10 cm. from Z, another thin piece of metal, U, having been slipped under the wire. This will allow the current to pass across from one wire to the other. Record the deflection in the col. marked 180. (C) Record the deflections for the lengths, 160 cm., 140, 120, 100, 80, and 60; then repeat (A) to be sure that the cell has been working uniformly. This deflection should agree with that in (A). (D) Change the direction of the current through G V; to do this, change wire, 1, from M P 2 to M P 1, and wire 5 to M P 2. This must be done without disturbing G V. (E) Repeat (A), (B), and (C), and record the deflections for the different lengths. (F) Get the average deflections. (G) Take, for future use, the deflection produced without G-S W being in the circuit. Swing the end of wire, 3, that is joined to Y, around to M P 2. The current will then pass simply through G V. Record deflection in col. marked O. =Note.= It is best to do the next experiment at once with the same cell, so that the results of the two experiments can be compared. In case this is impossible, get your cell to produce the same deflection when you use it again, as shown in col. O, Fig. 97. You can regulate the deflection of the needle of G V by varying the strength and quantity of the acid in P C. _=317. Discussion.=_ The resistance of a wire evidently depends (Exp. 121) upon its length. The _exact_ relation between resistance and length cannot be seen from these results, however, which are used in the next experiment. It will be shown later that in a wire, other things remaining the same, the resistance varies directly as its length.