THIS Theory has been confirmed to me by divers Experiments, but by none more remarkably than on the Evening of the Day I made those before-mention'd; when the Vapours, which in the Afternoon by the Sun's Heat, and a brisk Gale were dissipated, and the Air perfectly dry, descended again in great Plenty upon the Absence of both, and the Evening was very damp. For between seven and eight o'Clock, I attempted again the same Experiments in the same Manner, without being able to make any of them succeed; though all those mention'd in this Paper with others of less Note, were made in Half an Hour's Time. I AM the more particular in this, being willing to save the Labour of those, who are desirous of making these Kind of Trials; for although some of the lesser Experiments may succeed almost at any Time, yet I never could find that the more remarkable ones would succeed but in dry Weather. _I am, Gentlemen,_ _Your most obedient,_ _humble Servant,_ W. WATSON. _London, April 25. 1745._ [Illustration] TO THE ROYAL SOCIETY. GENTLEMEN, IN some Papers I lately did myself the Honour to lay before you, I acquainted you of some Experiments in Electricity; particularly I took notice of having been able to fire Spirit of Wine by what I call'd the repulsive Power thereof; which I have not heard had been thought of by any of those _German_ Gentlemen, to whom the World is obliged for many surprizing Discoveries in this Part of natural Philosophy. HOW far strictly speaking the Spirit in this Operation may be said to be fired by the repulsive Power of Electricity, or how far that Power, which repels light Substances when fully impregnated with Electricity, fires the Spirit, may probably be the Subject of a future Inquiry; but as I am unwilling to introduce more Terms into any Demonstration than what are absolutely necessary for the more ready Conception thereof, and as inflammable Substances may be fired by Electricity two different Ways, let the following Definitions at present suffice of each of these Methods. BUT first give me Leave to premise, that no inflammable Substances will take fire, when brought into or near the Contact of _Electrics per se_ excited to Electricity. This Effect must be produced by non-electrical Substances impregnated with Electricity received from the exciting _Electrics per se_. But to return, _1st_, I SUPPOSE that inflammable Substances are fired by the attractive Power of Electricity, when this Effect arises from their being brought near excited non-Electrics.