The following Memoir of Signor Palmieri on the eruption of Vesuvius in April of this year (1872), brief as it is, embraces two distinct subjects, viz., his narrative as an eye-witness of the actual events of the eruption as they occurred upon the cone and slopes of the mountain, and his observations as to pulses emanating from its interior, as indicated by his Seismograph, and as to the electric conditions of the overhanging cloud of smoke (so called) and ashes, as indicated by his bifilar electrometer, both established at the Observatory. The two last have but an indirect bearing upon Vulcanology. The narrative of the events of the eruption is characterised by exactness of observation and a sobriety of language--so widely different from the exaggerated style of sensational writing that is found in almost all such accounts--that I do the author no more than justice in thus expressing my view of its merits. Nor should a special narration, such as this, become less important or suffer even in popular estimation by the fact that so recently my friend, Professor J. Phillips, has given to the world the best general account of Vesuvius, in its historical and some of its scientific aspects, which has yet appeared. That monograph--with its sparkling style, and scholarly digressions, as well as for its more direct merits--will, no doubt, become the manual for many a future visitor to the volcanic region of Naples; but it, like the following Memoir of Palmieri, and in common with almost every work that has appeared on the subject of Volcanoes, contains a good deal which, however interesting, and remotely related to Vulcanology, does not properly belong to the body of that branch of cosmical science, as I understand its nature and limits. It tends but little, for example, to clear our views, or enlarge our knowledge of the vast mechanism in which the Volcano originates, and that by which its visible mass is formed, that we should ascertain the electric condition of the atmosphere above its eruptive cone, or into what crystallographic classes the mineral species found about it may be divided: it will help us but little to know Pliny's notions of how Pompeii was overwhelmed, or to re-engrave pictures, assumed to give the exact shape of the Vesuvian or other cone at different periods, or its precise altitude, which are ever varying, above the sea. Even much more time and labour may be spent upon analysing the vapours and gases of fumaroles and salfatares than the results can now justify. Nothing, perhaps, tends more to the effective progress of any branch of observational and inductive science, than that we should endeavour to discern clearly the scope and boundary of our subject.