The foregoing conclusions as to the masses of the positive and negative constituents of atoms had all been reached before 1900, mostly by the workers in the Cavendish Laboratory, and subsequent investigation has not modified them in any essential particulars. The history of the development of our present knowledge of the charges carried by the constituents will be detailed in the next chapters. [Pg 45] CHAPTER III EARLY ATTEMPTS AT THE DIRECT DETERMINATION OF Although the methods sketched in the preceding chapters had been sufficient to show that the mean charges carried by ions in gases are the same or nearly the same as the mean charges carried by univalent ions in solution, in neither case had we any way of determining what the absolute value of that mean charge is, nor, indeed, had we any proof even that all the ions of a given kind, e.g., silver or hydrogen, carry the same charge. Of course, the absolute value of could be found from the measured value of if only , the number of molecules in 1 c.c. of gas under standard conditions, were known. But we had only rough guesses as to this number. These guesses varied tenfold, and none of them were based upon considerations of recognized accuracy or even validity. I. TOWNSEND’S WORK ON The first attempt at a direct determination of was published by Townsend in a paper read before the Cambridge Philosophical Society on February 8, 1897.[29] Townsend’s method was one of much novelty and of no little ingenuity. It is also of great interest because it contains all the essential elements of some of the subsequent determinations. [Pg 46]