4.453
19.83
1.915
522.2
38
3.965
15.72
1.519
658.5
39
3.531
12.47
1.204
830.4
40
3.145
9.888
0.9550
1047.0
No. 10 pure copper wire weighs 31.43 pounds per 1000 feet.
WIRE DATA AND FORMULAE 375
(2) The Ohm.
1 international ohm = 1.06300 Siemens units.
1 international ohm = 1.01348 British Association (B.A.) units.
1 international ohm = 1.00283 legal ohms.
1 international ohm = resistance at C. of column of pure
mercury, 106.3 cms long, weighing
14.4521 grams, and of uniform cross-
section.
1 British Association unit (B.A.U.) = 0.986699 international
ohm.
1 legal ohm = 0.997178 international ohm.
(3) Resistance of Wire Wound in a Channel.
The following formula will enable the resistance to be calculated
for any wire with any thickness of insulation when wound to fill
a channel of any given volume. The formula assumes the wire
is wound in square order and in a regular manner. The formula
is approximate to the extent that terms which involve the square
of the thickness of the insulation are neglected We have
1.27 Vp,
R> ' 2F'
In relation (1) R t = ohms at t to which wire winds,
V = total volume of channel filled with wire,
Pt = resistivity of wire at t,
d = diameter of wire,
h = twice the thickness of the insulation.
Example. To what resistance will No. 26 B. & S. copper wire
wind per cubic centimeter, when its temperature is 20 C., and
the double thickness of its insulation is 5 mils?
In this case
V = 1 cu. cm,
P20 = 1.594 X 1.08 X 10-*,
d = 0.0405 cm,
h = 0.0127 cm (5 mils).
These values placed in relation (1) give
R t = 0.499 ohm.
376 APPENDIX
(4) Certain Formulae for Wire.*
The wire is pure copper and at 20 C.; bare.
(Ohms per 1000 feet) = 10354 -^ (area in cir. mils).
(Pounds per 1000 feet) = 0.0030269 X (area in cir. mils).
(Feet per pound) = 330,360 -r- (area in cir. mils).
(Ohms per pound) = 3,420,400 -f- (area in cir. mils) 2 .
(Feet per ohm) = 0.096585 X (area in cir. mils).
2
Area in circular mils = diameter in mils
For approximate calculations it may be easily remembered that
1000 feet No. 10 wire = 1 ohm,
1000 feet No. 13 wire = 2 ohms,
1000 feet No. 16 wire = 4 ohms, etc.,
1000 feet No. 7 wire = \ ohm,
1000 feet No. 4 wire = \ ohm,
1000 feet No. 1 wire = J ohm, etc.
To change microhms per centimeter-cube to ohms per mil-foot
multiply by 6.014. To change ohms per mil-foot to microhms
per centimeter cube multiply by 0.166. (Statement taken from
Catalogue J, Driver-Harris Wire Company.) f
IV. PHYSICAL DATA.
(1) Resistivity of Mercury.
The following data was furnished the author by the Bureau of
Standards. (In his own work the author has used the value,
volume resistivity of mercury at 20 C. = 95.782.)
The values for the resistivity of mercury are those computed
from the temperature formulae of F. E. Smith of the National
Physical Laboratory of England (Phil. Trans. 204, p. 112; 1904),
C. E. Guillaume of the International Bureau (Comptes Rendus,
115, p. 414; 1892), and Kreichgauer and Jaeger of the Reichsan-
stalt (Wied. Ann., 47, 527; 1892). In the following table volume
resistivity is given in microhms per centimeter cube and mass
resistivity is given in ohms per meter-gram.
* The constants under this heading are reproduced with the permission
of the Standard Underground Cable Company, of Pittsburgh, Pa., from their
"XVII Hand-Book, Standard Underground Cable Company, Copyright, 1906."
t Since the material given in Appendix III was prepared, the Bureau of
Standards has issued circular No. 31, entitled " Copper Wire Tables." This
circular should be consulted for the most authoritative information upon wire
sizes, standards, and temperature coefficients.
PHYSICAL DATA
377
Volume resistivity
Mass resistivity
0C.
20 C.
100 C.
0C.
20 C.
100 C.
Smith
94.073
94.073
94.073
95.783
95.782
95.782
103.410
103.379
103.56
12.7898
12.7898
12.7898
12.9751
12.9749
12.9748
13.8076
13.8034
13.828
Guillaume
Kreichgauer and
Jaeger
The C. values are computed from the quantities given in the
definition of the international ohm, 14.4521 grams mass and
106.300 centimeters length; and, in the case of volume resistivity
at C., the density is assumed to be such as to make the cross-
section 1 mm. 2 Smith's temperature formula was obtained from
observations between C. and 24 C., Guillaume's between C.
and 61 C., and Kreichgauer and Jaeger's between 14 C. and
28 C. Accordingly the values given for 100 C. are based on
extrapolation.
The temperature formula for mass resistivity is of course not
the same as for volume resistivity. Thus, letting d represent mass
resistivity, p volume resistivity, and d density,
^ = EL . $L.
do po do
The temperature formula of resistance, as measured in a glass
tube, is different from either of the temperature formulas .for
resistivity. Thus, letting 7 denote the resistance as measured in
a glass tube, and y g the linear coefficient of expansion of the glass,
7t = Pt . 1
7o po 1 + y g t
(2) Resistivities at 20 C.; Densities and Melting Points of the
Solid Elements.
Resistivity or the specific resistance is given in microhms. (To
change to ohms multiply by 10" 6 .) The resistivity is the ohmic
resistance between opposite faces of a centimeter cube of the sub-
stance. Resistivity is quite dependent upon the purity of the
material, which is not generally recorded. It is not useful, there-
fore, to record values beyond three, or at the most four, figures.
Where values given by different observers differ a mean value
is given here. The table is arranged in the order of decreasing
resistivity.
378
APPENDIX
Element
Resistivity
in mi-
crohms at
20 C.
Density,
grams per
cubic cen-
timeter
Melting temperature,
degrees C.
Bismuth
119*
9.80
269
Mercury
95. 782 f
13.5462
-38.80
Silicon
59.5
2.3
1200 (?)
Antimony
41 3
6 62
629 20 5 F P
Thorium
40 9
11 3
1690
Arsenic
38
5 73
volatilizes
Strontium . . .
25
2 54
900
Tellurium
21
6 25
450
Lead . .
20 96
11 37
327
Steel (1% C.)
20
7.8(?)
Thallium
19
11.9
301
Tantalum
14.7
16.6
2910(?)
Rubidium
12.3
1.53
38.5
Iron (0 1% C.)
12 1
7 86
1505 (about)
Tin
11 4
7 29
232
Tungsten (wire) ...
6-12
18 8
3002
Palladium . .
10 78
11 4
1549 22 F. P.
Calcium
10 5
1 55
780
Platinum
10 2
21 5
1755 05 F. P.
Cobalt
9.71
8 6
1489 82 F. P.
Nickel
9.52
8.9
1452 3 2. OF. P.
Osmium
9 5
22 5
2200
Lithium
9 0711
534
186
Indium
9
7 12
155
Cadmium ....
7 57
8 64
320 20 3 F. P.
Potassium .
7 11U
862
62 5
Zinc
6 1
7 1
418 20.3F.P.
Rhodium
6 04
12 44
1907
Iridium
5 34
22 41
2290
Sodium
4 87H
971
97
Magnesium
4.57K
1.723H
633
Molybdenum
4
8 6
very high
Aluminum
3
2 65
657
Gold
2 44
19 32
1062 40 8 F. P
Copper .
1 721
8 89
1082 60 8F. P.
Silver (99.9%)
1 65
10 5
960 00 7 F. P.
Barium
3 75
850
Beryllium
1 93
1430
Boron
2.5(?)
above 2000.
Caesium
1.87
26.4
Graphite, carbon
2 3
vaporizes at
Lanthanum
6 12
about 3720.
810
Manganese
7 39
1200 (about)
Neodymium
6 96
840
Sulphur (amorphous)*.
insulator
1 92
444 6 (boils).
Titanium
3 54
2500
Vanadium
5.5
1620
Zirconium
4 15
1300
* Changes in a magnetic field.
t See Appendix, IV, 1.
J Estimated. Value at 15 C.
40.1.
Estimated. Value at 0C. = 17.6.
|| Estimated. Value at C. = 8.4.
IT Author's value.
PHYSICAL DATA
379
The density of a substance may depend upon its previous treat-
ment and its physical state; hence values are generally not given
closer than three figures. The densities given are the grams per
cubic centimeter of the substance at room temperature and at
atmospheric pressure. When authorities differ a mean value is
given.
The melting point is given in degrees centigrade at which the
substance melts. In the case of several substances the melting
points are very sharp and have been determined with great care.
They serve as fixed points of temperature which are used for
reproducing the temperature scale. In these cases the symbol,
F.P., follows the recorded temperature; the numerical figure, as
db 0.8 states that the recorded temperature of melting is known
within that number of degrees centigrade.
(3) Data on a Few Alloys.
Alloy
Composition
Maker
Resis-
tivity in
mi-
crohms
at20C.
Temperature
coefficient
over small
range
Density
Driver- Harris
109 6
00016
8 02
Nichrome
Nickel steel
Wire Co.
96.6
87 1
0.00044
low
8.15
8 14
Constantan
German silver, 30%
60Cu+40Ni
30 Ni+Cu+Zn
49
48
0.00001
00023
8.88
Therlo
Manganin
German silver, 18% . .
Yankee silver
Platinoid
Cu+Mn+Al
84 Cu+4 Ni+12 Mn
18 Ni+Cu+Zn
62Cu+i5Ni+22Zn
;;
46.7
44.5
36
33
32 5
0.0000056
0.00002
0.0003
0.00028
00025
8.15
8.5
8.5
8.6
9
Ferronickel
28.2
0.002
8.2
Brass
70 Cu+30 Zn
6 to 9
0.001
8. 4 to 8. 7
(4) Standard Solutions for Calibrating Purposes. (See 1121.)
The table gives the resistivity p t at six temperatures t of NaCl t
and KC1 solutions.
The numbers -in the columns are resistivities. They express the
resistance in ohms of the solution (at the temperature in degrees C.
heading the column) between opposite faces of a centimeter-cube
of the solution. The reciprocals of the resistivities expressed in
ohms are conductivities expressed in mho, cubic centimeter, units.
[Note that the resistivity of a saturated solution is roughly one
million times the resistivity of a pure metal.]
n = normal solution.
380
APPENDIX
Thus, 1 n = normal KC1 = 74.59 gms. of the salt dissolved in
1 liter, at 18 C., of pure water.
NaCl, Sat. = saturated solution of NaCl at temperature head-
ing a column.
Solution
oc.
8C.
12 C.
16 C.
20 C.
24 C.
NaCl Sat
7 435
5 924
5 342
4 847
4 425
4 062
KC1, In...
15 ..288
12.572
11.509
10.592
9.797
9.104
KC1, O.ln
KC1, 0.02n
139.86
657.9
112.61
526.3
102.14
478.5
93.283
436.7
85.690
400.0
79.113
369.0
KC1, 0.01 n
1282.0
1031.0
934.6
852.5
782.47
721.50
(5) Resistivities of Insulators.
These vary so widely with the temperature, the purity and
character of the material, the state of the surface,* and the con-
ditions of the test, that the values given below are only roughly
approximate and merely serve to indicate the order of magnitude
of the quantities. Expressed in megohms resistance between
opposite faces of a cubic centimeter of the material the resistivities
of a few materials at ordinary temperatures are:
Paraffin wax = 3 X 10 12 ,
Mica = 9 X 10 9 ,
Ebonite = 2 X 10 9 ,
Porcelain, 50 C., = 2 X 10 9 ,
Rubber (used as insulation on wire) = 4.5 X 10 8 ,
f Fused Silica = 2 X 10 8 ,
t Glass (soda-lime) = 5 X 10 5 .
Consult par. 815.
National Physical Laboratory, England.
INDEX.
(Numbers refer to pages.)
A.
i values of, 363.
1000 -a
Accuracy, checked by using dif-
ferent methods, 6.
Ageing of thermometers, "304.
Alloys, data on, 379.
"Alternating Currents," Bedell and
Crehore, 205.
Alternating current, resistance de-
termined with, 199.
Alternating-current resistance, appa-
ratus to measure, 200.
error in measuring, considered, 206.
remarks upon, 199.
test of method of measuring, 207.
Aperiodic motion, 348.
Approximation formulae, 372.
Armagnat, H., 347.
Arrangements of rheostat coils, 81.
five plans described for, 81.
Assumptions, when using deflection
instruments, 20.
Ayrton shunt, 160.
errors in using, considered, 164.
full theory of, 160.
galvanometer constant obtained
with, 166.
insulation measurement using an,
167.
numerical illustrations in using an,
165.
table relating to, 161.
B.
Babcock, H. D., 327.
Balance, systematic method of ob-
taining, 97.
Batteries, curves for, 217.
Batteries, Continued.
internal resistance of, 214.
tested by condenser method, 215.
Battery, resistance of, by Kelvin's
method, 235.
resistance of, by Mance's method,
218.
resistance of, by Siemen's method,
236.
resistance of, by voltmeter and
ammeter methods, 220.
Battery resistance, alternating-cur-
rent methods of measuring,
226.
bridge method of measuring, elec-
trodynamometer detector, 230.
bridge method of measuring, tele-
phone detector, 226.
diminished deflection method, 233.
galvanometer deflection methods
of measuring, 233.
test of A. C. method of measur-
ing, 228.
Bedell and Crehore, 347.
Bell Telephone Company, 288.
Bell Telephone Company method,
248.
Bell Telephone Company test, 288.
Bimetallic conductors, conductivity
of, 368.
Bridge, Bureau's form for comparing
standards, 328, 329.
Bridge wire, calibration of, 70.
Bureau of Standards, 4, 148, 299, 301,
326.
Burgess, C. F., 29.
Burgess, method of, 29.
Bus-bar, measurement of current in,
108.
resistance of, 106.
381
382
INDEX
C.
Cable, insulation resistance per mile,
169.
Cables, faults on heavy underground,
284.
formula for calculating insulation
resistance of, 185.
insulation resistance of, 185.
Calibration of bridge wire, 70.
application of, 73.
coils used for, 71.
curve for, 73.
sample measurement, 75.
theory of method of, 72.
Callender and Griffiths, 298.
Capacities, comparison of, 285.
Capacity and resistance, theorem on
relation between, 186.
Capacity of conductors in cables, 285.
Cardew, Major, 156.
Cardew's electrometer method, 156.
Carey-Foster bridge, mechanical de-
sign of, 65.
standardization of bridge wire of,
68.
Carey-Foster method, connections
for, 61.
for comparing resistances which
differ considerably, 66.
methods for determining bridge
wire resistance in, 63.
shunt for bridge wire in, 65.
specimen readings made with, 67.
theory of, 62.
three bridge wires used in, 65.
unique feature of, 61.
uses of, 65.
Cell, standard cadmium, 3.
Celluloid, specific resistance of, 179.
Celluloid condenser, resistance of,
176.
C.G.S. System, conversion of units
in, 371.
Closed circuit, resistance measured
without opening, 103.
resistance of section of, 102.
Columbia dry cell, resistance tested,
229
Combinations of resistance coils, 80.
formulae for, 80.
Committee on dry cell test, 218.
Condenser, method of connecting a
variable, 182.
resistance of celluloid, 176.
standard, 3.
Condenser method of testing bat-
teries, 215.
Condensers, theory of leakage of,
170.
Conductance, defined, 132.
Conductivity, calculated from resist-
ance data, 148.
of bimetallic conductors, 368.
commercial measurement of, 140.
equipment for determining, 145.
determined with variable ratios,
. 150.
relation to temperature coefficient,
148.
standards of, 132.
Conductivity and resistance, rela-
tions between, 367.
Conductor considered as a conveyor
of energy, 133.
Conductors, general and specific
properties of, 136.
money value of, 370, 371.
Conjugate conductors, 51.
Connection, methods of ascertaining,
and fault location, 292.
Constant, arbitrary galvanometer,
168.
Contact resistances, expression for
errors due to, 79.
in arms of Wheatstone bridge, 78.
Conversions to different systems of
units, 371.
"Cooling curves," footnote, 345.
Copper wire, table for, 374.
weight of, per 1000 feet, 374.
Correction factor, errors by neglect-
ing, 119.
in formula of Kelvin double bridge,
118.
Corrections, methods of applying, in
loop test, 278, 280.
INDEX
383
Crosses, method of locating induc-
tive, 288.
Crosses or grounds, loop methods for
locating, 258.
Curves, of galvanometer motion, 348.
of insulation resistance, 195.
D.
Damping of galvanometer system,
348.
D'Arson, a unit, 356.
Data exhibited by curve, 5.
Decade, advantages of four coils to
the, 83, 85.
combinations of four coils to give,
84.
Decade plan, advantages of, 81.
Deflection indicator for measuring
temperature, 318.
Deflection instruments, low accu-
racy of, 16.
Densities of solid elements, 377.
Density of copper, 134.
Dial bridges for temperature meas-
urements, 314.
Differential circuits, application of, to
thermometry, 46.
practical advantages of, 45.
proof of a useful property of, 43.
properties of, 41.
Differential methods, 41.
assumptions made in, 42.
Differential galvanometer, for tem-
perature measurement, 312.
used with shunts, 48.
Diminished deflection method, 233.
Dry cells, report on methods of
testing, 217.
E.
e, functions of, 365.
Electric wiring system, insulation of,
210.
Electrical measurement, subjects con-
sidered under, 1.
Electrical Review, reference to, 79.
Electrical World and Engineer, ref-
erence to, 30.
Electrodynamometer, for battery re-
sistance, 230.
the Rowland, 200.
used in substitution method, 231.
Electrolytes, cell for containing, 245.
not measurable by direct current,
238.
resistance of, 238.
resistance of, by method of Kohl-
rausch, 240.
resistivities of, 244.
special bridge for measuring, 242.
Electrostatic induction, relation to
other quantities, 188.
Energy, money value of electrical, 6.
English-metric conversions, 365.
English Post Office bridge, 89.
Errors, absolute, 8.
accidental, 6.
calculation of, applied to deflec-
tion instruments, 14, 15.
calculation of, extended to several
variables, 10.
gross, 5.
mean, 8.
per cent, 9.
relative, 8.
systematic, 6, 7.
Evaluation by reading small deflec-
tions, 97.
F.
Factory testing set, 198.
Fault, distance to, in loop test, 260.
faulty wire of known length, two
good wires of unknown length,
267.
located with faulty wire and good
wire of unknown length, 277.
Fault finder, a lineman's, 294.
Fault-locating apparatus, the Fisher
set, 293.
Fault location, lead wires used in, 281.
practice and accuracy in, 290.
problems in, 253.
relation of principles to practice
in, 253.
384
INDEX
Fault location, Continued.
two faulty wires and one good
wire of unknown length, 276.
Faults, definition of, 251.
list of, 252.
location of, as opens, 284.
methods of locating, 251.
upon low-tension power cables, 283.
Feussner, decade system of, 87.
Fiber, specific resistance of, 183.
Figure of merit, defined, 354.
of galvanometers, 350.
unit of, 356.
Fisher, H. W., 267, 276, 293.
Fisher's loop test, modification of,
270.
Fisher's method, loop test when
length of cable is known, 269.
special case, 276.
Five-coil combinations, 86.
Formulae for conductivity, 137, 138,
139.
Four-coil arrangement of resistances,
Northrup's method, 82.
Four-coil arrangement used with dial
switches, 84.
Franklin Institute, Jour, of, foot-
note reference, 358.
Fundamental coefficient, defined, 299.
Fundamental interval, defined, 299.
G.
Galvanometer, arbitrary constant of,
168.
constant of, obtained with Ayrton
shunt, 166.
current reduction thru, by Ayrton
shunt, 162.
description of a high sensibility,
361.
Einthoven string, 357, 358, 359.
flat-coil pointer type, described,
340.
indicator in null methods, 40.
moving magnet and D'Arsonval
type of, 339.
portable pointer, used with ohm-
meter, 58.
Galvanometer, Continued.
portable type, for temperature
measurement, 311.
proportionality for flat-coil type,
345.
resistance of, measured by second
property of bridge, 69.
sensibility of pointer type, 340.
Galvanometer constants, table of, 360.
Galvanometer shunts, 157.
theory of ordinary, 157.
Galvanometer system, "dead parts"
of, 357.
equation of motion of, 346.
Galvanometers, comparison of, 349.
diverse qualities of, 350.
drawing of flat-coil type, 341.
flat-coil type of, 340.
sensitive, for insulation testing, 346.
Gas, expansion of, 297.
Graphite, resistivity of, 4.
Ground, located upon a single line,
253.
on single line, sample test, 257.
testing from each end of line for,
254.
testing from one end of line for, 255.
Grounds, location of, on high-tension
cables, 281.
resistance of, 248.
Grounds or crosses, loop methods for
locating, 258.
H.
Heraeus platinum, 302.
Herseus wire, purity of, 307.
Hering, Dr. Carl, 29.
Bering's conversion tables, 7.
Bering's liquid potentiometer, 247.
High resistance, electrometer method
for measuring, 175.
leakage method I for measuring,
171.
leakage method II for measuring,
175.
leakage method III for measuring,
180.
measured by leakage methods, 170.
INDEX
385
High resistance, measured by method
of mixtures, 180.
High resistances, capacity used in
measuring, 155.
deflection methods for measuring,
153.
galvanometer for measuring, 157.
measured with Wheatstone bridge,
153.
metallic resistances excluded from,
152.
specified and described, 152.
two general classes of, 152.
without appreciable capacity, 157.
High-tension cables, location of
grounds on, 281.
testing outfit for, 283.
Hoopes bridge, 140.
operations required in using, 143.
precautions in using, 144.
standards for, 142.
theory of, 141.
Humidity, effect of, on resistance
standards, 326.
I.
Inductive crosses, location of, 288.
Inertia, moment of, of galvanometer
system, 352.
Insulation measurements, factory
testing set for, 198.
with galvanometer and Ayrton
shunt, 167.
Insulation resistance, measured by
deflection methods, 191.
of a long cable, 191.
operations required in measuring,
by deflection, 191.
per mile of cable, 169.
Insulation resistance of a cable, for-
mula for calculating, 185.
Insulators, resistivities of, 380.
Instruments, distinction between in-
dicator and deflection, 338.
proposed treatment of, 324.
K.
Kelvin double bridge, a network of
nine conductors, 115.
Kelvin double bridge, Continued.
assembled from resistance boxes,
126.
correction factor in formula for, 118.
diagrams of, 116.
formula for, 118.
formula for sensibility of, 121.
methods of applying principle of,
123.
Otto Wolff's ratio coils for, 123.
ratio coils variable, 123.
standard variable, 125.
theory of, 117.
Kelvin's method, for measuring gal-
vanometer resistance, 69.
Kelvin- Varley slides, 75.
equivalent to a long slide-wire, 77.
Kempe's Handbook of Electrical
Testing, 53.
Kohlrausch, Dr. F., 30, 372.
Kohlrausch's method for resistivity
of electrolytes, 240.
L.
Landolt, etc., 246.
LeChatelier, 306.
Lead wires, resistance of, eliminated,
310.
used in fault location, 281.
Leakage methods, 170.
condition for highest precision, 173.
Leakage of condensers, theory of, 170.
Leeds, Morris E., 312.
Leeds and Northrup Co., 58, 101, 119,
126, 145, 146, 198, 200, 265,
283, 340, 359.
Lineman's fault finder, 294.
Live wires, methods of measuring
resistance of, 210, 212.
Loop methods, for locating grounds
or crosses, 258.
H. W. Fisher's method, 267.
modified to meet special condi-
tions, 267.
the Murray loop, 258.
Loop test, defined, 258.
Fisher's method with slide-wire
bridge, 269.
386
INDEX
Loop test, Continued.
from both ends of faulty wire, 271.
illustrative example, 274.
modifications of Fisher's method,
269.
position of galvanometer in, 259.
testing from one end when return
wire is of unknown resistance,
273.
testing with return wire of un-
known length, 271, 273.
testing from one end, method II, 274.
Loop tests, correction for conductors
of different sizes in, 280.
methods of applying corrections
in, 278, 280.
Lord Kelvin, 115.
Low resistance, distinguished from
medium, 100.
measured with ammeter and milli-
voltmeter, 101.
Low-resistance standards, set of pre-
cision, 101.
Low resistances, compared by Carey-
Foster bridge, 114.
compared by modified slide-wire
bridge, 114.
compared by potentiometer, 115.
Low-tension power cables, location
of faults upon, 283.
M.
Magnesium, conductivity of, 139.
resistivity of, 127.
Mains, resistance of underground, 110.
Mance's method, 218.
Manganin, temperature coefficient
of, 101.
Manganin resistance, 5.
Marine cable testing, 292.
Marvin, Prof. C. F., 299.
Matthiessen's standards of conduc-
tivity, 134.
relation between, 134.
Maxwell's rule, 96.