The work of photographing by the Wilson method the artificial disintegration of elements has been continued. In the earlier work, about 400,000 tracks of alpha particles in nitrogen were photographed and eight collisions were observed in which a proton was ejected and the alpha particle captured. This process was shown to correspond to the formation of a then unknown isotope of oxygen O 17 . Recently this isotope has been discovered spectroscopically in the atmosphere. Four more collisions of the same type have been observed by Harkins and his co-workers. There are two main objectives in such investigations. It is important to discover if the disintegration of elements other than nitrogen takes place also with the capture of the alpha particle, or whether disintegration without capture can occur. The Wilson method is the only direct method of doing this, since it is only thus that the motion of all the particles involved in the collision can be observed.