The foregoing remarks naturally lead us to the question whether changes are still going on upon the surface of our satellite: whether there is still left in it a spark of its volcanic activity, or whether that activity has become totally extinct. We shall consider this question from the observational and theoretical point of view. First as regards observations. This much may be affirmed indisputably—that no object or detail visible to the earliest selenographers (whose period may be dated 200 years back) has altered from the date of their maps to the present. When we pass from the bolder features to the more minute details we find ourselves at a loss for materials for forming an inference; the only map pretending to accuracy even of the larger among small objects being that of Beer and Maedler, which, truly admirable as it is, is not very safely to be relied upon for settling any question of alleged change, on account of the conventional system adopted for exhibiting the forms of objects, every object being mapped rather than drawn, and shown as it never is or can be presented to view on the moon itself. This difficulty would present itself if a question of change were ever raised upon the evidence of Beer and Maedler’s map: it may indeed have prevented such a question being raised, for certainly no one has hitherto been bold enough to assert that any portion or detail of the map fails to represent the actual state of the moon at the present time. In default of published maps, we are thrown for evidence on this question upon observations and recollections of individual observers whose familiarity with the lunar details extends over lengthy periods. Speaking for ourselves, and upon the strength of close scrutinies continued with assiduity through the past thirty years, we may say that we have never had the suspicion suggested to our eye of any actual change whatever having taken place in any feature or minute detail of the lunar surface; and our scrutinies have throughout been made with ample optical means, mostly with a 20-inch reflector. This experience has made us not unnaturally in some slight degree sceptical concerning the changes alleged to have been detected by others. Those asserted by Schroeter and Gruithuisen were long ago rejected by Beer and Maedler, who explained them, where the accuracy of the observer was not questioned, by variations of illumination, a cause of illusory change which is not always sufficiently taken into account. A notable instance of this deception occurred a few years ago in the case of the minute bright crater _Linné_, which was for a considerable period declared, upon the strength of observations of very promiscuous character, to be varying in form and dimensions almost daily, but the alleged constant changes of which have since been tacitly regarded as due to varying circumstances of illumination induced by combinations of libratory effects with the ordinary changes depending upon the direction of the