770 INDEX OF SUBJECTS. 



CHAPTER III. MEASUREMENT OF COUPLES. 



PAGE 



Torsion Couple 48 



Moments of Inertia 48 



Experimental Determination of Moments of Inertia and of Couples ... 51 



Unifilar Balance 54 



Determination of the Coefficient of Torsion 56 



Coefficients of Elasticity and of Tenacity 58 



Influence of Temperature on Torsion 59 



Silk Threads 59 



Bifilar Balance 60 



Influence of the Rigidity of the Wires . . . . , 63 



Influence of the Points of Support 66 



Influence of Temperature 67 



Comparison of the Unifilar with the Bifilar Balance 67 



CHAPTER IV. PROPERTIES OF CIRCULAR 

 CURRENTS. 



Circular Cylindrical Coils 71 



Length of the Wire. Mean Radius 72 



Volume and Weight of the Wire 73 



Resistance 74 



Surface. Magnetic Moment 75 



Electromagnetic Action 77 



Action at a Point on the Axis 78 



Most Suitable Dimensions for a Rectangular Channel 80 



Coil of Maximum Action for a Given Source 81 



Best Form of the Channel 84 



Wire of Variable Diameter 87 



Action of a Circular Current Outside the Axis 90 



Action of a Coil Outside the Axis 93 



Action of a Coil at a Small Distance 96 



Action of a Coil at a Great Distance 98 



Action of a Long Coil 99 



Maxwell's Method 101 



Action of a Coil on a Magnetic Needle 102 



Gaugain's Coil 105 



Von Helmholtz's Arrangement 106 



Coil with Four Circles 108 



Coil with Three Circles 1 10 



Two Circles with Currents in Opposite Directions in 



Mean Actions in 



Annular Coil 113 



