_Example._ We see from the table that the resistance of about 39 ft. 1 in. of No. 24, B and S copper wire is 1 ohm. This equals 469 in. If 469 in. have a R (resistance) of 1 ohm, 1 in. will have a R of one-469th of an ohm; that is 1 divided by 469, which equals a little over .002 ohm. For every inch of No. 24 wire used, then, for connections, we may allow .002 ohm. This will be near enough for our purposes. Suppose that each connection is 18 in. long, the regular wires with connectors being used. The R of the 36 in. joined to R C will then be 36 times .002 = .072 ohm. Our standard R must then be considered as 2.072 ohm. If we substitute this in the example, as stated in § 328, we have 3.7 × X = 6.3 × 2.072. X must equal (6.3 × 2.072)/3.7 = 3.528 ohm, which includes the unknown resistance and 36 in. of connections, the R of which is .002 ohm; 3.528 - .072 = 3.456, the resistance of X alone. Compare this with the answer to example, § 328. Make allowances according to length of connectors used. _=Note.=_--Carefully keep all the results of these experiments in a note book for future reference. Be sure that connections are good. =EXPERIMENTS 127-137. To measure the resistances of various wires, coils, etc., by the "bridge method."= _Apparatus._ The coils of wire, etc., as stated in the "Directions" of each experiment. The details of each piece of apparatus may be found by referring, from the numbers given, to the "Apparatus List," and to descriptions in the paragraphs mentioned. Also all the apparatus of Exp. 126. =Note.= Make proper allowances for connections (§ 330) in all experiments in measuring resistances. =EXPERIMENT 127.= =331. Directions.= (A) As explained in Exp. 126, measure the resistance of the 10-turn coil of G V, allowing for connections (§ 330). Read the bridge-scale carefully. (B) Use one-half of the 2-ohm coil as standard and repeat. =EXPERIMENT 128.= =332. Directions.= (A) Measure the resistance of the 5-turn coil of G V (see Exp. 126, etc.), using 2 ohms as standard. (B) Use 1 ohm as standard, repeat, and compare results. (C) Add the resistances of the 5 and 10-turn coils, and compare the sum with the resistance of the 15-turn coil, as found in Exp. 126, D. The difference should be but a few hundredths of an ohm. =EXPERIMENT 129.= =333. Directions.= (A) Measure the resistance of the coil of No. 24 copper wire (No. 89). This coil is used for later experiments. Spring connectors are fastened to the ends of this coil, allowing it to be directly connected to the conductor on the bridge, so no allowance should be made for its connecting wires. (See Exp. 126 for details.) Mark the resistance upon the coil for future use. (See Note.)