Article		Page
462.	J. A. Broun’s method of correction John Allan Broun (1817–1879) was a Scottish meteorologist and magnetician known for his work on magnetic variations.	115
463.	Joule’s suspension James Prescott Joule’s method for suspending magnetic needles to reduce friction.	115
464.	Balance vertical force magnetometer	117

CHAPTER VIII.

Article		Page
465.	Elements of the magnetic force	120
466.	Combining the results of a country's magnetic survey	121
467.	Deriving the expansion of the earth’s magnetic potential using spherical harmonics A mathematical method for representing physical fields on the surface of a sphere.	123
468.	Definition of the earth’s magnetic poles. They are not located at the ends of the magnetic axis. False poles: they do not exist on the earth’s surface	123
469.	Gauss’s calculation of the 24 coefficients for the first four harmonics	124
470.	Distinguishing between external and internal causes of magnetic force	124
471.	Solar and lunar variations	125
472.	Periodic variations	125
473.	Magnetic disturbances and their 11-year cycle Referring to the correlation between magnetic storms and the solar sunspot cycle.	126
474.	Reflections on magnetic investigations	126

PART IV.

Article		Page
475.	Örsted’s discovery of how an electric current affects a magnet Hans Christian Örsted discovered in 1820 that electric currents create magnetic fields.	128
476.	The space near an electric current is a magnetic field	128
477.	The effect of a vertical current on a magnet	129
478.	Proof that the force from an infinitely long straight current is inversely proportional to the distance	129
479.	Measuring current using electromagnetic units	130