178. In Parts III. and IV. of my first series of papers under this title (Transactions of the Royal Society for February 1856), I described experiments discovering effects of stress on the thermo-electric quality and the electric resistances of metals. About the time those experiments were made I also made several nugatory attempts to discover the effects of stress on magnetization; and eighteen years have passed before I have been able to resume the investigation. Early in the year 1874 I made arrangements to experiment on the magnetization of iron and steel wires in two different ways—one by observing the deflections of a suspended magnetic needle produced by the magnetization to be tested, the other by observing the throw of a galvanometer-needle, due to the momentary current induced by each sudden change of magnetism. The second method, which for brevity I shall call the ballistic method, was invented by Weber, and has been used with excellent effect by Thalén, Roland, and others. It has great advantages in respect of convenience, and the ease with which accurate results may be obtained by it; but it is not adapted to show slow changes of magnetism, and is therefore not fit for certain important parts of the investigation. On this account I am continuing arrangements for carrying out the first method, although hitherto I have obtained no good results by it. 179. On the other hand, I have found the ballistic method very easy and perfectly satisfactory in every respect, except that it does not show the slow changes of magnetization. It was by it that all the results which I am now going to describe were obtained. The apparatus, which is very simple, is represented in the accompanying sketch (fig. 1).