440 POPULAR SCIENCE MONTHLY. 



the precautions suggested by experience in measuring the resistance of 

 electrolytes. Indeed, such was the reputation of Cavendish for scien- 

 tific 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 Kohl- 

 rausch has since shown to be nearly accurate, that for weak solutions 

 the product of the resistance by the percentage of salt is nearly con- 

 stant, and also stated accurately the laws of multiple and divided cur- 

 rents, 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 equiva- 

 lent 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 Eichter's 'Anfangsgrimde 

 der Stochyometrie' was not published till 1792, while Cavendish's ex- 

 periments 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. 



