I shall not, in this place, enter on any exposition of the general principles which regulate the illumination of Lighthouses, and still less will it be proper to discuss the advantages of the different methods of illumination by Reflection and Refraction, as I shall, in the sequel, find a more convenient opportunity for speaking somewhat in detail on those subjects. It will be enough to present a very brief notice of the improvements in the mode of illuminating Lighthouses, which the Northern Lights Board have introduced since 1824, up to which time, as already mentioned, a sketch of their works is already before the public. One of the most important changes in Lighthouse apparatus was, unquestionably, the introduction of Revolving Lights at the Tour de Corduan about the year 1780, by which the means of distinguishing one light from another were greatly extended, and a marked difference in the appearance of contiguous lights was at once simply obtained. The mere variation of the velocity of the revolution is so simple as to afford an obvious source of distinction among lights; and yet it is remarkable, that it was only lately that one of its principal advantages was perceived by my Father, who first applied it in the year 1827 as a means of distinction for the Light of Buchanness. This distinction consists in giving the frame a greater number of sides or faces, and a more rapid revolution, so as to cause a flash in every five seconds of time, which produces an effect so marked and characteristic as to afford by far the most effective distinction which has been exhibited since the introduction of Revolving Lights. Under the auspices of the Board, this distinction has been since applied at the Rhinns of Islay Lighthouse, and has given much satisfaction wherever it has been tried. The late King of the Netherlands, a great patron of the useful arts, was so much pleased with this device that he presented the author of it with a splendid gold medal, in token of his approbation. The only other improvement on the Reflecting Lights, which I shall notice in this place, is that called the _intermittent light_, which is due to the same officer, and was by him introduced at the stations of Mull of Galloway, Tarbetness, and Barrahead. It consists of the apparatus of a fixed Light, in front of which two cylindric shades are alternately shut and opened by a vertical movement, so as to produce a sudden extinction and exhibition of the light, in a manner very difference from the gradual decline and growth of the flash, which is produced in revolving Lights by the attenuating effects of divergence on the penumbral portions of the light reflected from the mirror. ~Dioptric Lights.~