This thesis is divided into two parts; Part I consisting of the theory and Part II the experimental work. Part I is divided into three sections; in Section 1 a summary is given of collision processes and how they have been used to explain various experimental results; this is followed in Section 2 by the author's interpretation of some previous experimental observations; a summary of the wave mechanical theory of collisions is given in Section 3. Part II consists of four sections; In Section 1an outline is given of the various ways of exciting spectra and this is followed by a description of the apparatus used by the author in Section 2; the results of the experiments with hydrogen and oxygen are given in Section 3, and the theoretical interpretation of these; the last Section deals with the experiments carried out with hydrogen and helium, and the facts which may be inferred from these experimental results.