to
. He published as his final value
. In 1903, however,[36] he published some new work on
in which he had repeated the determination, using the radiation from radium in place of that from X-rays as his ionizing agent and obtained the result
. He explained the difference by the assumption that in his preceding work the more active negative ions had monopolized the aqueous vapor available and that the positive ions had not been brought down with the cloud as he had before assumed was the case. He now used more sudden expansions than he had used before, and concluded that the assumption made in the earlier experiments that the number of ions was equal to the number of particles, although shown to be incorrect for the former case, was correct for these second experiments. As a matter of fact, if he had obtained only half the ions in the first experiments and all of them in the second, his second result should have come out approximately one-half as great as the first, which it actually did. Although Thomson’s experiment was an interesting and important modification of Townsend’s, it can scarcely be said to have added greatly to the accuracy of our knowledge of