맥스웰의 전기에 관한 기초 논문.The Book of An elementary treatise on electricity by James Cl erk Maxwell

AN
ELEMENTARY TREATISE
ON
ELECTRICIT Y
BY
JAMES CLERK MAXWELL, M.A.
LL.D. EDIN., D.C.L., F.R.SS. LONDON AND EDINBURGH
HONORARY FELLOW OF TRINITY COLLEGE
AND PROFESSOR OF EXPERIMENTAL PHYSICS IN THE UNIVERSITY OF CAMBRIDGE
EDITED BY
WILLIAM GARNETT, M.A.
FORMERLY FELLOW OF ST. JOHN’S COLLEGE, CAMBRIDGE
SECOND EDITION
Oxford
AT THE CLARENDON PRESS
1888

맥스웰.James Clerk Maxwell,1831.6.13-1879.11.5. 영국 물리학. 출생지,영국 에든버러. 주요저서,전자기학1873.
15세가 되기 전에 난형곡선卵形曲線에 관한 논문을 에든버러왕립학회에 제출. 에든버러대학에 진학하여 회전곡선의 이론, 탄성고체의 평형平衡 등의 논문을 쓰고, 1850년 케임브리지대학에서 공부. 1855년 펠로로 선출되었으며, 색채론과 전자기학을 연구했다. 1856년 애버딘대학 자연철학 교수가 되었다. 이 무렵 토성고리의 연구로 애덤스상을 받았으며, 1860년까지 재직하다가 런던의 킹스칼리지로 옮겼다. 1865년 병을 얻어 교수직을 그만두기까지의 5년간 색채론에 관한 연구를 하면서 전자기학 이론의 기초가 되는 물리적 지력선指力線 전자기의 장場의 역학 등의 논문을 완성. 상이한 온도 및 압력에서의 공기의 점성粘性에 관한 연구를 비롯하여 기체의 분자운동론에 관한 중요한 연구가 이루어졌으며, 전기저항의 단위를 결정하기 위한 실험적 연구. 사직 후 커쿠브리셔의 글렌레어로 돌아가 명저 전자기학(1873)을 발표하고, 열학熱學에 관한 간단한 저술도 했다. 그 무렵 케임브리지대학에서는 대학총장 데번셔공公의 기부금으로 1871년 교수직이 개설되고, 맥스웰이 실험소 설립을 담당. 이것이 캐번디시연구소이며, 1874년 연구소 개설과 함께 맥스웰이 소장이 되었다. 전자기학에서 거둔 업적은 장場의 개념의 집대성이다. 패러데이의 고찰에서 출발하여 유체역학적 모델을 써서 수학적 이론을 완성하고, 유명한 전자기장의 기초방정식인 맥스웰방정식(전자기방정식)을 도출하여 그것으로 전자기파의 존재에 대한 이론적인 기초를 확립. 전자기파의 전파속도가 광속도와 같고, 전자기파가 횡파라는 사실도 밝힘으로써 빛의 전자기파설의 기초를 세웠다(1873). 전자기파는 이후 헤르츠에 의해 실험적으로 입증.
기체의 분자운동에 관한 연구도 빛나는 업적이다. 당시까지의 분자의 평균속도 대신 분자속도의 분포를 생각하며 속도분포법칙을 만들고, 그 확률적 개념을 시사함으로써 통계역학의 기초를 닦았다(맥스웰볼츠만의 분포법칙). 기체의 점성률에서는 분자의 평균자유행로의 개념을 도입하기도 하였다. 1879년 케임브리지에서 암으로 사망.

맥스웰의 전기에 관한 기초 논문.The Book of An elementary treatise on electricity by James Cl erk Maxwell

CONTENTS.
??
CHAPTER I.
Art.
Page
1. Exp. I. Electrification by friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. ? II. Electrification of a conductor . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ? III. Positive and negative electrification . . . . . . . . . . . . . . . . . . . . 4
4. ? IV. Electrophorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Electromotive force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Potential of a conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Of metals in contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Equipotential surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Potential, pressure, and temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11. Exp. V. Gold-leaf electroscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
12. ? V. Gold-leaf electroscope?continued . . . . . . . . . . . . . . . . . . . . . 12
13. Quadrant electrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
14. Idio- and Hetero-Static . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
15. Insulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
16. Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
CHAPTER II.
ON THE CHARGES OF ELECTRIFIED BODIES.
17. Exp. VI. Electrified body within a closed vessel . . . . . . . . . . . . . . . . 17
18. ? VII. Comparison of the charges of two bodies . . . . . . . . . . . . . 18
19. ? VIII. Electrification of inside of closed vessel equal and op-
posite to that of enclosed body . . . . . . . . . . . . . . . . . . . . . . . 19
20. ? IX. To discharge a body completely . . . . . . . . . . . . . . . . . . . . . . . 20
21. ? X. To charge a body with a given number of times a particular
charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
22. Five laws of Electrical phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
I. In insulated bodies.
II. In a system of bodies during conduction.CONTENTS.
ix
Page
Art.
III. In a system of bodies during electrification.
IV. Electrification of the two electrodes of a dielectric equal
and opposite.
V. No electrification on the internal surface of a conducting
vessel.
CHAPTER III.
O N E L E C T R I C A L W O R K A N D E N E R G Y.
23. Definitions of work, of energy, of a conservative system . . . . . . . . . 23
24. Principle of conservation of energy. Examples of the measurement
of work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
25. Definition of electric potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
26. Relation of the electromotive force to the equipotential surfaces . . 25
27. Indicator diagram of electric work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
28. Indicator diagram of electric work?continued . . . . . . . . . . . . . . . . . . 26
29. Superposition of electric effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
30. Charges and potentials of a system of conductors . . . . . . . . . . . . . . . 28
31. Energy of a system of electrified bodies . . . . . . . . . . . . . . . . . . . . . . . . 29
32. Work spent in passing from one electrical state to another . . . . . . . 30
?? ????
33. ?? = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
????
34. ∑(?? ?? ′ ) = ∑(?? ′ ?? );?Green’s theorem . . . . . . . . . . . . . . . . . . . . . . . . 32
35. Increment of energy under increments of potentials . . . . . . . . . . . . . . 32
?? ????
36. ?? = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
????
37. Reciprocity of potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
38. Reciprocity of charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
39. Green’s theorem on potentials and charges . . . . . . . . . . . . . . . . . . . . . . 35
40. Mechanical work during the displacement of an insulated system . 37
41. Mechanical work during the displacement of a system the potentials
of which are maintained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37CONTENTS.
x
Page
Art.
CHAPTER IV.
THE ELECTRIC FIELD.
42. Two conductors separated by an insulating medium . . . . . . . . . . . . . 40
43. This medium called a dielectric medium, or, the electric field . . . . 40
EXPLORATION OF THE ELECTRIC FIELD.
44. Exp. XI. By a small electrified body . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
45. Exp. XII. By two disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
46. Electric tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
47. Exp. XIII. Coulomb’s proof plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
48. Exp. XIV. Electromotive force at a point . . . . . . . . . . . . . . . . . . . . . . . 45
49. Exp. XV. Potential at any point in the field. Two spheres . . . . . . . . 45
50. Exp. XVI. One sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
51. Equipotential surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
52. Reciprocal method. Exp. XVII. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
53. Exp. XVIII. Method founded on Theorem V. . . . . . . . . . . . . . . . . . . . 48
54. Lines of electric force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
CHAPTER V.
F A R A D A Y ’ S L AW O F L I N E S O F I N D U C T I O N .
55. Faraday’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
56. Hollow vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
57. Lines of force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
58. Properties of a tube of induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
59. Properties of a tube of induction?continued . . . . . . . . . . . . . . . . . . . . 52
60. Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
61. Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
62. Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
63. Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
64. Analogies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
65. Analogies?continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
66. Limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
67. Faraday’s cube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59CONTENTS.
xi
Page
Art.
68. Faraday’s cube?continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
69. Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
70. Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
71. Theorems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
72. Induction and force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
73. + and ? ends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
74. Not cyclic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
75. In the inside of a hollow conducting vessel not containing any elec-
trified body the potential is uniform and there is no electrification 63
76. In the inside of a hollow conducting vessel not containing
any electrified body the potential is uniform and there is no
electrification?continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
77. Superposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
78. Thomson’s theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
79. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
80. Induced electricity of 1st and 2nd species . . . . . . . . . . . . . . . . . . . . . . 65
CHAPTER VI.
PARTICULAR CASES OF ELECTRIFICATION.
81. Concentric spheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
82. Unit of electricity. Law of force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
83. Electromotive force at a point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
84. Definition of electromotive force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
85. Coulomb’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
86. Value of the potential due to a uniformly electrified sphere . . . . . . 72
87. Capacity of a sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
88. Two concentric spherical surfaces. Leyden Jar . . . . . . . . . . . . . . . . . . 76
89. Two parallel planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
90. Force between planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
91. Thomson’s attracted disk electrometers . . . . . . . . . . . . . . . . . . . . . . . . . 79
92. Inverse problem of electrostatics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
93. Equipotential surfaces and lines of force for charges of 20 and 5
units (Plate I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81CONTENTS.
xii
Page
Art.
94. Equipotential surfaces and lines of force for opposite charges in the
ratio of 4 to ?1 (Plate II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
95. Equipotential surfaces and lines of force for an electrified point in
a uniform field of force (Plate III) . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
96. Equipotential surfaces and lines of force for charges of three elec-
trified points (Plate IV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
97. Faraday’s use of the conception of lines of force . . . . . . . . . . . . . . . . 84
98. Method employed in drawing the diagrams . . . . . . . . . . . . . . . . . . . . . 86
CHAPTER VII.
ELECTRICAL IMAGES.
99. Introductory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
100. Idea of an image derived from optics . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
101. Electrical image at centre of sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
102. External point and sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
103. Two spheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
104. Calculation of potentials when charges are given . . . . . . . . . . . . . . . . 96
105. Surface density induced on a sphere by an electrified point . . . . . . 97
106. Surface density on two spheres and condition for a neutral line . . . 99
CHAPTER VIII.
C A P A C I T Y.
107. Capacity of a condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
108. Coefficients of condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
109. Comparison of two condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
110. Thomson’s method with four condensers . . . . . . . . . . . . . . . . . . . . . . . . 103
111. Condition of null effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
CHAPTER IX.
ELECTRIC CURRENT.
112. Convection current with pith ball . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
113. Conduction current in a wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
113. No evidence as to the velocity of electricity in the current . . . . . . . 109CONTENTS.
xiii
Page
Art.
114. Displacement and discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
115. Classification of bodies through which electricity passes . . . . . . . . . 111
Definition of the conductor, its electrodes, anode, and cathode . . . 111
External electromotive force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Metals, electrolytes, and dielectrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
1. Metals.
116. Ohm’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
117. Generation of heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
2. Electrolytes.
118. Anion and cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Electrochemical equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
119. Faraday’s Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Force required for complete electrolysis . . . . . . . . . . . . . . . . . . . . . . . . 114
120. Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
121. Helmholtz’s experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
122. Supposed inaccuracy of Faraday’s Law not confirmed . . . . . . . . . . . 116
123. Measurement of resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Ohm’s Law true for electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
124. Theory of Clausius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
125. Theory of Clausius?continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
126. Velocities of ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
127. Molecular conductivity of an electrolyte . . . . . . . . . . . . . . . . . . . . . . . . 119
128. Kohlrausch’s experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
129. Secondary actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
3. Dielectrics.
130. Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
131. Dielectric capacity of solids, including crystals . . . . . . . . . . . . . . . . . . 122
132. Dielectric capacity of solids, liquids, and gases . . . . . . . . . . . . . . . . . 123
133. Disruptive discharge. Mechanical and electrical analogies. Ultimate
strength. Brittleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
134. Residual charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
135*. Mechanical illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125CONTENTS.
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Page
Art.
136. Electric strength of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
137. Gases as insulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
138. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
139. Mercury and sodium vapours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
140. Kinetic theory of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
141. Electric phenomena of Tourmaline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
142. Electric glow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
143. Electric windmill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Electrified air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Motion of thunder-clouds not due to electricity . . . . . . . . . . . . . . . . . . 134
144. To detect the presence of electrified air . . . . . . . . . . . . . . . . . . . . . . . . . 134
145. Difference between positive and negative electricity . . . . . . . . . . . . . 135
146. Discharge by a point on a conductor electrified by induction . . . . . 135
147. The electric brush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
148. The electric spark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
149. Spectroscopic investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
150*. Description of the voltaic battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
151*. Electromotive force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
152*. Production of a steady current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
153*. Magnetic action of the current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
154*. The galvanometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
155*. Linear conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
156*. Ohm’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
157*. Linear conductors in series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
158*. Linear conductors in multiple arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Kirchhoff’s Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
159*. Resistance of conductor of uniform section . . . . . . . . . . . . . . . . . . . . . 144
CHAPTER X.
PHENOMENA OF AN ELECTRIC CURRENT WHICH FLOWS THROUGH
HETEROGENEOUS MEDIA.
160. Seebeck’s discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
161. Law of Magnus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
162. Thermoelectric diagram and definition of thermoelectric power . . . 146
163. Electromotive force measured by an area on the diagram . . . . . . . . 147CONTENTS.
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Art.
164. Cumming’s discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
165. Thermal effects of the current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
166. Peltier’s effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
167. Thomson’s effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
168. Thomson’s analogy with a fluid in a tube . . . . . . . . . . . . . . . . . . . . . . . 151
169. Le Roux’s experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
170. Expression of Peltier’s and Thomson’s effects . . . . . . . . . . . . . . . . . . . 152
171. Heat produced at a junction depends on its temperature . . . . . . . . . . 152
172. Application of the second law of thermodynamics . . . . . . . . . . . . . . . 153
173. Complete interpretation of the diagram . . . . . . . . . . . . . . . . . . . . . . . . . 153
174. Entropy in thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
175. Electric entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
176. Definition of entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
177. Electric entropy equivalent to thermoelectric power . . . . . . . . . . . . . 155
178. Thermoelectric diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
179. Specific heat of electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
180. Difference between iron and copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
181. Complete interpretation of the diagram . . . . . . . . . . . . . . . . . . . . . . . . . 158
182. Thomson’s method of finding the E. M. F. at a point in a circuit . 159
183. Determination of the seat of electromotive force . . . . . . . . . . . . . . . . 160
184. E. M. F. between metal and electrolyte . . . . . . . . . . . . . . . . . . . . . . . . . 160
185. Electrolysis. Deposition of metal. Solution of metal . . . . . . . . . . . . . 161
186. Heat generated or absorbed at anode and cathode . . . . . . . . . . . . . . . 162
187. On the conservation of energy in electrolysis . . . . . . . . . . . . . . . . . . . 164
188. Joule’s experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
189. Loss of heat when current does external work . . . . . . . . . . . . . . . . . . 165
190. Electromotive force of electrochemical apparatus . . . . . . . . . . . . . . . . 165
191. Reversible and irreversible effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
192. Example from electrolysis of argentic chloride . . . . . . . . . . . . . . . . . . 166
193*. On constant voltaic elements. Daniell’s cell . . . . . . . . . . . . . . . . . . . . . 168
CHAPTER XI.
METHODS OF MAINTAINING AN ELECTRIC CURRENT.
194. Enumeration of methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173CONTENTS.
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Page
Art.
195. The frictional electric machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
196. On what the current depends. Use of silk flaps . . . . . . . . . . . . . . . . . . 174
197*. Production of electrification by mechanical work. Nicholson’s re-
volving doubler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
198*. Principle of Varley’s and Thomson’s electrical machines . . . . . . . . . 176
199*. Thomson’s water-dropping machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
200. Holtz’s electrical machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
201*. Theory of regenerators applied to electrical machines . . . . . . . . . . . . 181
202*. Coulomb’s torsion balance for measuring charges . . . . . . . . . . . . . . . 183
203*. Electrometers for measuring potentials. Snow-Harris’s and Thom-
son’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
204*. Principle of the guard-ring. Thomson’s absolute electrometer . . . . 187
205*. Heterostatic method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
206*. Measurement of the electric potential of a small body . . . . . . . . . . . 193
207*. Measurement of the potential at a point in the air . . . . . . . . . . . . . . . 194
208*. Measurement of the potential of a conductor without touching it . 195
CHAPTER XII.
ON THE MEASUREMENT OF ELECTRIC RESISTANCE.
209*. Advantage of using material standards of resistance in electrical
measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
210*. Different standards which have been used and different systems
which have been proposed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
211*. The electromagnetic system of units . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
212*. Weber’s unit, and the British Association unit or Ohm . . . . . . . . . . . 197
213*. Professed value of the Ohm 10,000,000 metres per second . . . . . . . 197
214*. Reproduction of standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
215*. Forms of resistance coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
216*. Coils of great resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
217*. Arrangement of coils in series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
218*. Arrangement in multiple arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
219*. On the comparison of resistances. (1) Ohm’s method . . . . . . . . . . . . 202
220*. (2) By the differential galvanometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
221*. (3) By Wheatstone’s Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207