opposite direction to the first. The two images being then viewed in a stereoscope, would appear as a solid sphere, in which condition we should doubtless get such an acquaintance with the surface of our satellite as can be obtained by no other means. The reason for taking the images with so long an interval between is, that although each one represents the same object, each must be taken at a different angle; and for an object so distant as the moon, the difference caused by the libration would, it is believed, be sufficient for the desired result. In the small pictures, however, the difference of angle is so slight, that to the unpractised observer they appear precisely alike; it is, nevertheless, essential to the effect that the variation, though minute, should exist. With respect to the pseudoscope--which makes the outside of a teacup appear as the inside, and the inside as the outside; which transforms convexity into concavity, and the reverse; and a sculptured face into a hollow mask; which makes the tree in your garden appear inside your room, and the branches farthest off come nearest to the eye; and which, when you look at your pictures, represents them as sunk into a deep recess in the wall,--with respect to this instrument, its practical uses have yet to be discovered. But as your celebrated countryman, Sir David Brewster, is working at the subject, as well as Mr Wheatstone, we shall not, so say the initiated, have to wait long for further results. Besides these lectures, a course is being delivered at the Museum of Practical Geology, recently opened in Jermyn Street, by eminent professors, as you may judge from the fact of De la Beche, Forbes, and Playfair being among them. Some of the most promising of the pupils at the School of Design are allowed to attend these lectures gratis. At the same institution, an attempt is to be made to do what has long been done in Paris--namely, to admit working-people to the best scientific lectures free of cost. Now, therefore, is the time for the working-men of the metropolis to shew whether they wish for knowledge and enlightenment or not. They have only to present themselves at the Museum, pay a registration-fee of sixpence, conform to the rules, and so qualify themselves for the course of six lectures. It is a capital opportunity; and I, for one, hope that hundreds of the intelligent working-men of London will avail themselves of it. They, on their part, may find government education not unacceptable; and government, on the other hand, encouraged by a successful experiment, may feel inclined to extend its benefits. If a clear-headed lecturer on political economy could also be appointed, perhaps in time our industrial fellow-countrymen might come to understand that strikes are always a mistake, and the masters, that fair play is a jewel.