Several workers have previously investigated the magnetic properties of copper and aluminium, but in most cases too small regard has been paid to the changes in magnetic susceptibility brought about by mechanical and thermal treatments previous to measurements. In the present work I have attempted to correlate changes in the magnetic susceptibilities of copper and aluminium with metallurgical changes in the metal lattices. A somewhat tentative theory is outlined covering this correlation. Previous investigations by Kussmann and Seeman led to the conclusion that iron impurity in the pure copper was the sole cause of the various magnetic changes recorded. This it is hoped to disapprove. To get some insight into the changes caused by such ferromagnetic impurity a series of magnetic measurements were carried out on low iron content iron-copper alloys, very kindly supplied by Imperial Chemical Industries Ltd., “Metals Division”. The thesis falls naturally into four main parts, and appendices are added at the end to avoid interpolation of the work with definitions etc. Throughout the thesis (Parts III and IV) only a few experimental values, typical of the many results obtained, are quoted.