xiv Contents 



THOUGHTS CONCERNING ELECTRICITY P . 110 



From MS. No. 18. (Probably an early draft of the theory) 



ARTICLES 



Hypothesis of an electric fluid . . 195 



The fluid acts at a distance but does not itself extend to any perceptible distance from 



electrified bodies 196 



Proof of this, and objections to the hypothesis of electric atmospheres . . . 197 



On the hypothesis of electric atmospheres .198 



Condition of electric equilibrium between conductors in electric communication . 199 

 Illustration from the equilibrium of air ......... 200 



Definitions of positive and negative electrification, and of over and under charge . 201 



Four hypotheses 202 



Cor. I, 2. Effect of two overcharged bodies approaching each other . . . . 203 



Cor. 3, 4. Equally electrified bodies repel 204 



Cor. 5. Electrification by induction . . . . . . . . . . 205 



Cor. 6. Theory of condensers 206 



Shock of the Leyden vial 207 



Fifth hypothesis, on the communication of electricity between conductor and the 



surrounding air 208 



Effect of an overcharged body 209 



Attraction and repulsion of electrified bodies 210 



Electrification by induction . . . . . . . . . . .211 



The electric spark 212 



Vacuum formed by the spark 213 



Statement of the theory of one electric fluid ....... 214-216 



ACCOUNT OF THE EXPERIMENTS . . P . 118 



(i) INVESTIGATION OF THE LAW OF FORCE 

 From MS. No. 7 (apparently prepared for publication) 



The electricity of glass is here taken to be positive 217 



First experiment. A globe within a hollow globe and in communication with it does 



not become over or undercharged when the whole is electrified (Fig. 12) . . 218 

 General description of the apparatus . . . . . . . . . .219 



General plan of the experiment ........... 220 



The apparatus actually used 221 



Mechanism for performing the required operations 222 



The charging jar 223 



The gauge electrometer ............ 224 



Reason for using the jar 225 



Theory of the experiment ............ 226 



Result of the experiment ............ 227 



Second method of trying the experiment 228 



Advantages of the second method 229 



Estimation of the degree of accuracy of the result 230 



The charge of the inner globe is less than Js f tnat f tne outer globe . . . 23 1 

 Hence the electric force is inversely as the square of the distance . . . .232 



Demonstration of this by Lemma 4 (Fig. 13) . 233 



Limits between which the law of force must lie, n = 2 ^5 . . . . . 234 



Second experiment. A piece of wood within a vessel formed of two wooden drawers 235 



