A CONVERSATION I had with Prof. Bragg, of the Adelaide University, in passing through Adelaide last summer suggested some thoughts in regard to the nature of the α rays which may be of interest in view of Prof. Rutherford's letter in last week's NATURE. Prof. Rutherford announces that he has at last succeeded in detecting the positive charge carried by the α rays of radium by using a magnetic field to deflect and remove the slow-moving electrons present with the α particles. He says, “I think these experiments undoubtedly show that the α particles do carry a positive charge, and that the previous failures to detect this charge were due to the masking action of the large number of slow-moving electrons emitted from the plates.” These results, while they afford a welcome confirmation of the conclusions drawn from the evidence of the magnetic and electric deviation suffered by the α rays, do not, to my mind, finally settle the question.