Dr. Wilson, being a man of influence, succeeded in having his views taken up by the Board of Ordnance. It has been remarked that this controversy would never have attracted attention but for the fact that the discoverer of the effect of points was Franklin. He was an American and the dispute with the colonies was then at its height. The war of the Revolution had begun, and the British forces had already met with serious reverses. No patriot could, therefore, admit any good in points. George III. took sides, decreed that the points on the royal conductors at Kew should be covered with balls, and ordered Sir John Pringle to support Dr. Wilson. Sir John gave the dignified answer: "Sire, I cannot reverse the laws and operations of nature"; to which the King, incensed that so incompetent a man should hold such an important office, replied: "Then, Sir John, perhaps you had better resign," which Sir John did.
A wit of the time put the matter epigrammatically when he wrote:
"While you, great George, for knowledge hunt
And sharp conductors change to blunt,
The nation's out of joint;
Franklin a wiser course pursues,
And all your thunder useless views
By keeping to the point."
It was in connection with this heated controversy that Franklin wrote the following admirable words:
"I have never entered into any controversy in defence of my philosophical opinions. I leave them to take their chance in the world. If they are right, truth and experience will support them; if wrong, they ought to be refuted and rejected. The King's changing his pointed conductors for blunt ones is, therefore, a matter of small importance to me."
It was not until September, 1752, that Franklin raised a rod over his own house. This experimental conductor was made of iron fitted with a sharp steel point and rising seven or eight feet above the roof, the other end being buried five feet in the ground. In order to avoid useless personal displacement, Franklin, the economist of time, made an automatic annunciator similar to that devised by Gordon in 1745, and described by Watson in his Sequel, 1746, to apprize him of the advent of a good thunder-gust. Instead of making the rod of one continuous length, it was divided on the staircase, opposite his chamber door, the ends being drawn apart to a horizontal distance of a few inches. Screwing a pair of tiny gongs to the ends, he suspended between them a brass ball, held by a silk thread, to act as clapper. Whenever a thundercloud came hovering by, the bells began to ring, thereby summoning the philosopher to his "laboratory" on the staircase.
Franklin's rod, erected over his house in the summer of 1752, was evidently intended by him for experimental rather than protective purposes. There is no doubt whatever in his mind about the use of such pointed conductors for the protection of buildings and ships against the destructive effects of lightning. He expressly says, in an article printed in Poor Richard's Almanack for 1753, that "It has pleased God in His infinite goodness to mankind, to discover to them the means of securing their habitations and other buildings from mischief by thunder and lightning. The method is this: provide a small iron rod (it may be made of the rod-iron used by the nailers), but of such a length, that one end being 3 ft. or 4 ft. in the moist ground, the other may be 6 ft. or 8 ft. above the highest part of the building. To the upper end of the rod fasten about a foot of brass-wire, the size of a common knitting needle, sharpened to a fine point; the rod may be secured to the house by a few small staples. If the house or barn be long, there may be a rod and point at each end, and a middling wire along the ridge from one to the other. A house thus furnished will not be damaged by lightning, it being attracted by the points and passing through the metal into the ground without hurting anything. Vessels also, having a sharp-pointed rod fixed on the top of their masts, with a wire from the foot of the rod reaching down round one of the shrouds to the water, will not be hurt by lightning."
It is well known, as Dr. Rotch, Director of the Blue Hill Observatory, recently pointed out, that the matter for these almanacs was prepared by Franklin himself under the pen-name of Richard Saunders. As the above passage appeared in the almanac for 1753, it is obvious that it must have been ready sometime toward the end of 1752. Furthermore, we know that it was actually in the hands of the printer in the middle of October of that year, for the Pennsylvania Gazette of Oct. 19th says that the almanac was then in press and that it would be on sale shortly. Whence it follows that the year 1752 is the year of the invention of the lightning rod, and not 1753 or 1754 as often stated.
The instructions given by Franklin include all the essentials necessary for the erection of a lightning conductor. It may be made of iron or copper, flat or round, but must make good "sky" and good "earth." The former condition is secured by screwing to the top of the rod either copper or platinum terminals ending in sharp points; and the latter, by burying the lower end deep in moist soil. Between "sky" and "earth" the rod must be continuous.
The function of the rod is twofold, as Franklin well recognized, preventive and preservative. It prevents the stroke, under ordinary conditions, by the action of the points, which send off copious streams of air and dust particles electrified oppositely to that of the cloud. Even at a distance, the dangerous potential of the cloud is reduced by these convection currents and the stroke ordinarily averted. It is clear that ten points are more efficacious than one, and fifty more than five. Hence the number of points which we see distributed over the higher and more conspicuous parts of a building, all of which are carefully connected with the lightning conductor.