Torbern Olof Bergman (1735-1784), Swedish mineralogist and chemist. Autograph letter signed to the physicist Jean-Baptiste Le Roy (1720-1800), member of the Académie des Sciences and inventor of the first positive and negative electric machine ever used. 3 pp. folio. Upsala, 18 October 1763. Address on the back with wax seal. In Latin. Very long and important scientific letter, in Latin, entirely devoted to electrical experiments and the work of Benjamin Franklin, with mathematical formula. "[...] Electrica vero imprimis adfero, nam et te hisse labiribus invigilarescio, et meam quoz qualemcunq operan per aliquot annos (quantum alia negotia siverint) exercuerunt. Systema Franklinianum mox mihi valde arrisit, cum inde mira facilitate et congruentia phoenomena miche nota explicari possent, interim tamen quin absg ulteriori examine hance amplecter hypothesin, veritatis prohibuit amor. Huic itag scrutinio multum impendi temporis, conclusiones ex Franklini principiis colligendo, harumg cum experimentis comparatione. De duobus, usg contratrus elextricitatis generibus, multa variag experimenta memet plene convicerunt, sed quid de natura electricitatis sic dicta neativa vel resinosa sit sta tuendum, adhuo dubius hiereo [...] Inveni legem ab aliis detecham, quod numurum utrag simul generetur, plerumg veram asse, nonnullas tamen reperi exceptions, quas proxima vice commemorabo. Vidi quog parvas circumstantias friciones sape etficere, ut quod libet ex confricatis pro lubitu fieri potess vel pritivum vel negativum. Dominus Wilson tales varias ante me observavit, sed quod interdum calor idem prastet, adhut nemo, quantum scio, probavit [...]".