NO present Advantage accrued to those Persons, or to that Age, which first discover'd the Properties of the Magnet. Many hundreds of Years intervened, before they were applied to the great Uses of Navigation. Had these remain'd a secret till now, what other Methods could have been substituted in their Place, by which we could securely traverse the vast Ocean? All the Advantages we receive from distant Commerce, we must still have been Strangers to, but for this fortunate Application of the magnetical Power. And even the Discoveries thus far had been very imperfect, without the Knowledge of the Variation of the Compass. But the present Age, and even this Nation, boasts of a Gentleman[[1]], who seems to be entrusted with the magnetical Powers themselves. He makes artificial Magnets, increases in a few Minutes the Powers of real ones to a surprizing Degree, changes at Pleasure their Poles, and makes that newly acquired Polarity, permanent. The World, I hope, will not long be deprived of the Manner, by which these extraordinary Changes are produced, which as yet this Gentleman thinks proper to conceal. As Electricity has some Properties in common with Magnetism, as will be shewn in the Course of these Observations; some new Lights probably may be thrown upon both. But to return; admitting even, that no substantial Advantages could arise from the Inquiries before us, (which, however, we can by no means grant, upon our considering the Effects we already perceive of its Operations upon human Bodies) whatever tends to enlarge the Conceptions of the Mind, and to implant in us still more lofty Ideas of the Almighty Author of Nature, deserves certainly, independent of other Considerations, our highest Regard.
THESE Experiments were all made with Glass Tubes of about two Foot long; the bore about an Inch in Diameter. But a scrupulous Exactness in these Proportions is no ways necessary. The thinner and lighter these Tubes are, the sooner they are excited; though they, 'tis true, don't retain their Power so long as those, which are more thick and substantial. But where you intend to communicate the electrical Power, as fast as you excite it, I should prefer a light Tube; though it ought never to be less than 1/12 of an Inch thick, because of the Danger of breaking it by the Friction.
THE Tube, before it is rubbed, should be always made dry and warm, which may be done by laying it before the Fire. But I cannot omit hereupon making one further Remark; viz. that Glass Tubes, exactly of the same Dimensions, made at the same Time, and with the same Materials, vary considerably with regard to their fitness for electrical Purposes. Clear and dry Air with some degree of cold is most eligible, though I have succeeded in the greatest Fogs, but with more Difficulty.
TO
Martin Folkes, Esq;
P. R. S.
SIR,
THE Society having heard from some of their Correspondents in Germany, that what they call a Vegetable Quintessence had been fired by Electricity, I take this Opportunity to acquaint you, that on Friday Evening last I succeeded, after having been disappointed in many Attempts, in setting Spirits of Wine on Fire by that Power. The preceding Part of the Week had been remarkably warm, and the Air very dry, than which nothing is more necessary towards the Success of Electrical Trials; to these I may add, that the Wind was then Easterly and inclining to freeze. I that Evening used a glass Sphere as well as a Tube; but I always find myself capable of sending forth much more Fire from the Tube than from the Sphere, probably from not being sufficiently used to the last.
I had before observ'd, that although[[2]] Non-electric Bodies made electrical, lose almost all that Electricity by coming either within or near the Contact of Non-electrics not made electrical; it happens otherwise with Regard to Electrics per se, when excited by rubbing, patting, &c; because from the rubbed Tube I can sometimes procure five or six Flashes from different Parts, as though the Tube of two Foot long, instead of being one continued Cylinder, consisted of five or six separate Segments of Cylinders, each of which gave out its Electricity at a different Explosion.
The Knowledge of this Theorem is of the utmost Consequence towards the Success of electrical Experiments; inasmuch as you must endeavour by all possible Means to collect the Whole of this Fire at the same Time. Professor Hollman seems to have endeavour'd at this and succeeded, by having a tin Tube, in one End of which he put a great many Threads, whose Extremities touch'd the Sphere when in Motion, and each Thread collected a Quantity of electrical Fire, the Whole of which center'd in the tin Tube, and went off at the other Extremity. Another Thing to be observ'd, is to endeavour to make the Flashes follow each other so fast, as that a Second may be visible before the First is extinguish'd. When you transmit the electrical Fire along a Sword or other Instrument, whose Point is sharp, it often appears as a Number of disseminated Sparks, like wet Gunpowder or Wild-fire; but if the Instrument has no Point, you generally perceive a pure bright Flame, like what is vulgarly call'd the Blue-ball, which gives the Appearance of Stars to fired Rockets.
The following is the Method I made use of and was happy enough to succeed in. I suspended a Poker in silk Lines; at the Handle of which I hung several little Bundles of white Thread, the Extremities of which were about a Foot at right Angles from the Poker. Among these Threads, which were all attracted by the rubbed Tube, I excited the greatest electrical Fire I was capable, whilst an Assistant near the End of the Poker held in his Hand a Spoon, in which were the warm Spirits. Thus the Thread communicated the Electricity to the Poker, and the Spirit was fired at the other End. It must be observ'd in this Experiment, that the Spoon with the Spirit must not touch the Poker; if it does, the Electricity without any flashing is communicated to the Spoon, and to the Assistant in whose Hand it is held, and so is lost in the Floor.