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CCCCLXXXV: FROM M. DE SAUSSURE 1 - Benjamin Franklin, The Works of Benjamin Franklin, Vol. VI Letters and Misc. Writings 1772-1775 
The Works of Benjamin Franklin, including the Private as well as the Official and Scientific Correspondence, together with the Unmutilated and Correct Version of the Autobiography, compiled and edited by John Bigelow (New York: G.P. Putnam’s Sons, 1904). The Federal Edition in 12 volumes. Vol. VI (Letters and Misc. Writings 1772-1775).
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FROM M. DE SAUSSURE1
Naples, 23 February, 1773.
I have received with the greatest pleasure the two letters, which you did me the honor to write to me; the one of October the 8th, the other of December 1st. As they were both addressed to me at Geneva, and as I left that place at the beginning of October to come to Italy to pass the winter, they reached me very late, and I have thus been debarred the privilege of showing you, by a prompt reply, how much I feel flattered by the honor of your correspondence. The letter on the action of pointed conductors, and the accompanying Essay, contain experiments and reasonings perfectly conclusive, and which leave no doubt as to the utility of these ingenious preservatives.
If I had been acquainted with these new experiments, I should have made use of them with great advantage in a short apologetic memoir, which I published in October, 1771, for the information of some people who were terrified at a conductor which I had erected at Geneva before the house I lived in. This memoir, however, met with the desired success. It reassured everybody, and I had the pleasure of watching the electricity from the clouds during the whole course of the last summer. Several persons even followed this example, and raised conductors either upon their houses or before them. M. de Voltaire was one of the first. He does the same justice to your theory that he did to that of the immortal Newton.
The project of the Royal Society is well worthy of the zeal of that illustrious body for the advancement of useful knowledge; and I should be much pleased if I could in any way aid them in the execution of this project.1 Had I been at Geneva, I should have made it my duty and pleasure to take a journey to the mountains in the neighborhood, to ascertain with precision the dimensions of the mountains and valleys which I thought best suited for the execution of this design. I do not believe, however, that, among those with which I am acquainted, there is any place exactly suited to give certain information on the subject to which their researches are directed. In the Jura, there is no summit sufficiently high, since the Dole, the mountain which rises highest above the level of our lake, does not reach seven hundred toises above this level.
Then it must be considered that the Jura, as well as the Alps, form continued chains of mountains, all connected together, or, at least, situated at very short distances from each other. There is no single mountain, or, at least, I know of none, of sufficient height. You often find deep valleys, surrounded by high mountains, but behind these mountains are other valleys and other mountains, so that the deviations which might be observed in the plumb-line, would be the complex effect of the combined attractions of all these mountains; and, in order to deduce from them a comparison between the density of the earth and that of these mountains, much labor and many calculations would be required. As far as I am able to judge, it appears to me that some large rock, rising out of the open sea, like the Peak of Teneriffe, would be the most suitable place for this attempt.
The memoir upon this subject, which you did me the honor to send, I have transmitted to Lord Stanhope, at Geneva, that he may confer respecting it with M. de Luc, who, having attended particularly to the height of mountains, in connection with his observations of the barometer, is the best man in the world to give valuable information on this subject. It is now, doubtless, well known that Signor Beccaria of Turin, who has measured a degree of the meridian at the foot of the Alps, has had an opportunity to observe great deviations of the plumb-line, and would thus be enabled to furnish useful hints to the Royal Society.
I have the pleasure of often seeing here Sir William Hamilton, who has the kindness to take me to the most interesting places in the neighborhood of Naples, those which establish his theory of volcanoes ancient and modern, and prove that the whole Bay of Naples, from the sea to the Apennines, has been thrown up from the bottom of the sea by subter ranean fires, and is thus the product of volcanoes rather than the theatre of their ravages. We are also much devoted to electricity. The little machine, which Mr. Nairne made for him, is really excellent, and much the best they have ever had in this part of Italy. Sir William Hamilton, knowing that I had the honor of writing to you, has requested me to present his compliments.
I regret extremely that I was not at Geneva to receive M. de Normandy. I should have been delighted to have had this opportunity to prove to you how highly I value your recommendation. If you have any commands for me in Naples, I shall still be able to receive them here, and you may address them to Sir William Hamilton. We propose to try together some experiments on the electricity of the vapors of Vesuvius, although, to say the truth, I regard them merely as conductors, which establish a communication between the earth and the higher regions of the atmosphere.
Sir William Hamilton has also done me the kindness to invite me to witness some experiments he has tried with the torpedo. These experiments are not decisive, because the fishes we had were small, and gave only slight shocks, but no sign whatever of electricity appeared. We are waiting for some larger ones, in order to continue this investigation, according to the mode which you have yourself marked out.
Accept my assurances of the high consideration and esteem with which I have the honor to be,
[1 ]M. de Saussure was the well-known professor at Geneva, celebrated for his philosophical writings, and for his ascent of Mont Blanc.—Ed.
[1 ]To ascertain the lateral attraction of mountains, with the view of determining the mean density of the earth upon the Newtonian theory of gravitation. On this subject, it would seem, Dr. Franklin had written to request the aid of M. de Saussure, who had bestowed much time and attention in observing the geological structure and formation of the mountains of the Alps.