Page:Popular Science Monthly Volume 59.djvu/450

440 the precautions suggested by experience in measuring the resistance of electrolytes. Indeed, such was the reputation of Cavendish for scientific accuracy, that his bare results were accepted at once and readily became a part of general knowledge, although no one conjectured by what method he had obtained them, more than forty years before the invention of the galvanometer, the only instrument by which any one else has ever been able to compare electrical resistances. In carrying out this work Cavendish not only arrived at the result, which Kohlrausch has since shown to be nearly accurate, that for weak solutions the product of the resistance by the percentage of salt is nearly constant, and also stated accurately the laws of multiple and divided currents, but he even anticipated, in January, 1781, the law of electrical resistance, discovered independently by Ohm and published by him in 1827. Moreover, in a very remarkable set of experiments on a series of salts and acids in order to determine their relative electric resistance, Cavendish tells us, 'that the quantity of acid in each should be equivalent to that in a solution of salt in twenty-nine of water,' and it is difficult to account for agreement not only of the ratios, but also for the absolute numbers given by Cavendish with those of the modern system, in which the equivalent weight of hydrogen is taken as unity. They must have been derived from his own work, for Wenzel's 'Lehre von der Verwandschaften' was published in 1777, and also gives values greater than those used by Cavendish, and Richter's 'Anfangsgrunde der Stochyometrie' was not published till 1792, while Cavendish's experiments were made in 1777. It is only by comparing the dates of these researches with the dates of the principal discoveries in chemistry that we become aware that in the incidental mention of these numbers we have the sole record of one of those secret and solitary researches, the value of which to other men of science Cavendish does not seem to have taken into account after he had satisfied his own mind as to the facts. He dealt with his discoveries as with his great wealth, allowing the larger part of them to lie unused.