New experiments.�Paradoxes inferred from them.�Difference in the electricity of a globe of glass charged, and a globe of sulphur.�Difficulty of ascertaining which is positive and which negative. 261 Probable cause of the different attractions and repulsions of the two electrified globes mentioned in the two preceding letters. 264 Reasons for supposing, that the glass globe charges positively, and the sulphur negatively.�Hint respecting a leather globe for experiments when travelling. ibid. Electrical kite. 267 Hypothesis, of the sea being the grand source of lightning, retracted.�Positive, and sometimes negative, electricity of the clouds discovered.�New experiments and conjectures in support of this discovery.�Observations recommended for ascertaining the direction of the electric fluid.�Size of rods for conductors to buildings.�Appearance of a thunder-cloud described. 269 Additional proofs of the positive and negative state of electricity in the clouds.�New method of ascertaining it. 284 Electrical experiments, with an attempt to account for their several phenomena, &c. 286 Experiments made in pursuance of those made by Mr. Canton, dated December 6, 1753; with explanations, by Mr. Benjamin Franklin. 294 Turkey killed by electricity.�Effect of a shock on the operator in making the experiment. 299 Differences in the qualities of glass.�Account of Domien, an electrician and traveller.�Conjectures respecting the pores of glass.�Origin of the author's idea of drawing down lightning.�No satisfactory hypothesis respecting the manner in which clouds become electrified.�Six men knocked down at once by an electrical shock.�Reflections on the spirit of invention. 301 [xiii] Beccaria's work on electricity.�Sentiments of Franklin on pointed rods, not fully understood in Europe.�Effect of lightning on the church of Newbury, in New England.�Remarks on the subject. 309 Notice of another packet of letters. 313 Extract of a letter from a gentleman in Boston, to Benjamin Franklin, Esq. concerning the crooked direction, and the source of lightning, and the swiftness of the electric fire. 314 Observations on the subjects of the preceding letter.�Reasons for supposing the sea to be the grand source of lightning.�Reasons for doubting this hypothesis.�Improvement in a globe for raising the electric fire. 320 Effect of lightning on captain Waddel's compass, and the Dutch church at New York. 324 Proposal of an experiment to measure the time taken up by an Electric spark, in moving through any given space. 327 Experiments on boiling water, and glass heated by boiling water.�Doctrine of repulsion in electrised bodies doubted.�Electricity of the atmosphere at different heights.�Electrical horse-race.�Electrical thermometer.�In what cases the electrical fire produces heat.�Wire lengthened by electricity.�Good effect of a rod on the house of Mr. West, of Philadelphia. 331