CONTENTS.

Article		Page
194.	Application to two cases of the flow of electricity in a conducting sheet	239
195.	Application to two cases of electrical induction	239
196.	Capacity of a condenser A device for storing electrical energy, now commonly called a capacitor. consisting of a circular disk between two infinite planes	240
197.	Case of a series of equidistant planes cut off by a plane at right angles to them	242
198.	Case of a furrowed surface	243
199.	Case of a single straight groove	243
200.	Modification of the results when the groove is circular	244
201.	Application to Sir William Thomson’s guard-ring Sir William Thomson, later Lord Kelvin, was a preeminent physicist who developed precise measuring instruments.	245
202.	Case of two parallel plates cut off by a perpendicular plane. (Figure XII)	246
203.	Case of a grating of parallel wires. (Figure XIII)	248
204.	Case of a single electrified wire transformed into that of the grating	248
205.	The grating used as a shield to protect a body from electrical influence	249
206.	Method of approximation applied to the case of the grating	251

CHAPTER XIII.

Article		Page
207.	The frictional electrical machine	254
208.	The electrophorus of Volta An early instrument used to generate electrostatic charge via induction, invented by Alessandro Volta.	255
209.	Production of electrification by mechanical work—Nicholson’s Revolving Doubler	256
210.	Principle of Varley’s and Thomson’s electrical machines	256
211.	Thomson’s water-dropping machine	259
212.	Holtz’s electrical machine	260
213.	Theory of regenerators applied to electrical machines	260
214.	On electrometers and electroscopes. Indicating instruments and null methods. Difference between registration and measurement	262
215.	Coulomb’s Torsion Balance for measuring charges	263
216.	Electrometers for measuring potentials. Snow Harris’s and Thomson’s	266
217.	Principle of the guard-ring. Thomson’s Absolute Electrometer	267
218.	Heterostatic method A method of measurement where the instrument requires an auxiliary independent electrification to function.	269
219.	Self-acting electrometers—Thomson’s Quadrant Electrometer	271
220.	Measurement of the electric potential of a small body	274
221.	Measurement of the potential at a point in the air	275