than those to which the members of our own system are subjected.” The clearness with which this telescope exhibits every object within its range is so great that the most distant nebulæ are seen with as great distinctness as the nearest planet. On directing it towards the moon, which is only distant from us about 240,000 miles, the surface of our satellite may be explored with a facility almost as great as that with which we examine the details of a landscape with an ordinary telescope. Maedler, a German astronomer, who has measured nearly every mountain and valley on the moon’s surface with the greatest exactitude, stated some years before Lord Rosse’s telescope was perfected that if a monument as large as one of the Pyramids existed on the surface of the moon it could have been readily distinguished by the instruments then in use. With Lord Rosse’s telescope we can see the surface of our satellite so much enlarged that a space 220 feet square could be readily perceived by a good observer. This enormous eye, measuring 6 feet in diameter, would hardly show us a lunar elephant; but it is certain that if a troop of buffaloes, or animals analogous to them, crossed the field of vision, they would undoubtedly be perceptible. Masses of troops marching backwards and forwards would also be plainly visible, and we may assert with something like absolute certainty that there are neither towns nor villages in the moon, nor any buildings as large as St. Paul’s of London or the colossal railway stations of that metropolis. This telescope, as we have said before, is the largest hitherto constructed, and cost its noble constructor more than 25,000_l._ It must also be recollected that it was not a mere scientific toy belonging to an amateur philosopher, but a real working instrument in the possession of a true man of science, who did work with it that will render his name famous while civilization lasts. The present Lord Rosse seems worthy in every way of his father’s great name, and has already enriched astronomical science with numerous valuable observations. We shall finish this chapter by a description of the Newtonian telescope constructed by M. Léon Foucault. The mirror, instead of being made of speculum metal, which is an alloy of tin and copper, is made of glass from the famous manufactory of St. Gobain. The first rough grinding having been finished, it passed into the workshops of M. Secrétan, the optician to the Paris Observatory, to receive its final polish and finishing touches from the hand of M. Foucault himself, the most careful optical tests being applied to it before the commencement of each operation.