Experiments made with gun-cotton shewed conclusively that the cotton was ‘loudest of all;’ and ‘fired in the focus of the reflector, the gun-cotton clearly dominated over all the other sound-producers.’ The reports were heard at distances varying from two to thirteen miles and a half. When the fog clears off, the noisy signals are laid aside and bright lights all round the coast guide the seaman on his way. Some years ago the old oil light was superseded by the magneto-electric light, and this in turn has given place to the dynamo-electric light, which excels all in brilliance and intensity. In this machine the required movements are effected by steam or water power; and when the electric current is thereby generated, it is conducted by wires to a second machine, which co-operates in the work with remarkable economy and efficiency. Readers desirous of knowing the improvements made in the dynamo-electric machines by Messrs Siemens, and the experiments carried on in lighthouses, should refer to the _Proceedings_ of the Institution of Civil Engineers for the present session. Particulars of a galvanic battery of extraordinary power have been brought to this country from the United States. Instead of the carbon plate commonly used as one of the elements in the cells, it has a copper plate coated with lead and platinum; and a blowing apparatus is so combined that a stream of air can be blown through the acid liquid with which the cells are filled. The effects of this aeration are remarkable: the galvanic current is rendered unusually powerful, and a large amount of heat is developed. The way in which these effects are produced is not yet satisfactorily made out; but that this battery offers a new and potent means of investigation to chemists and physicists cannot be doubted. An account of an exclusively metallic cell has been given to the Royal Society by Professors Ayrton and Perry of the Engineering College, Tokio, Japan, in a paper on ‘Contact Theory of Voltaic Action.’ They took strips of platinum and magnesium, which were in connection with the electrodes of the electrometer, and dipped them into mercury, and immediately saw evidence of a strong current. The experiments were continued with much care until the Professors felt assured that ‘the electro-motive force obtained was about one and a half times the electro-motive force of a Daniell’s cell.’ ‘It may be possible,’ they remark further, ‘by mechanical or other means, or by using another metal than magnesium, to give constancy to this arrangement; and as its internal resistance is extremely small, the cell may be of great practical use for the production of powerful currents.’