In some parts of Italy, it is remarked by that eminent physician and philosopher, Dr James Johnstone, in his admirable volume, entitled the Diary of a Philosopher, which, by the way, is a work of rare virtue, in so much as it is replete, not only with accurate medical knowledge, but with reflections in literature and the fine arts such as prove an intimacy with polite learning not always found, that fever and that general unwholesome state of body, observed in districts infested with vitiated air, prevail where inquiry has discovered no appearance of unusual dampness and corruption of the soil. He thinks that streams of putrid water, containing animal and vegetable materials, that have sunk down from the surface, in some part of their course are making their way at a little depth, and that when the soil, parched with excessive heat and drought, becomes rent, as it commonly does, the emanations previously confined rush out by the channels now presented by these fissures, and deal their deadly effects around. Such an explanation seems to me highly probable, and deserving of more inquiry. Connected with this subject, the following facts may be interesting, and assist in forming an estimate of the probability of the truth of that explanation. In mines, as well as on the surface of the earth, changes are constantly going on; and as in the latter situation the animal, vegetable, and mineral components of the soil are decomposing, so the minerals in the former are giving out some of their component parts and abstracting oxygen, &c. in turn from the atmosphere. In mines some of the fossils attract oxygen from the air, but the chief process by which the atmosphere becomes vitiated there, is by the evolution of gases from the minerals. In coal pits the principal gases emitted are carbonic acid gas, commonly known as fixed air, which will support neither animal life nor combustion, as proved by the disastrous results on men having been confined in it, and by the extinction of light when immersed therein, and carburetted hydrogen gas, known as fire-damp, which cannot support respiration, and which takes fire when brought in contact with a light. These gases are the results of chemical changes going on in the minerals, in the same way as the gases before alluded to attend the decomposition of animal and vegetable substances. These gases arise not only from the minerals exposed to view at the various surfaces, as the roof, sides, and pavement of coal pits, but issue also from the unworked minerals in the interior, by fissures or cracks in the various strata, produced by the violence used in detaching the minerals. These fissures extend in the course of the beds, or strata, and are often scarcely visible, but are sometimes so wide as to admit the finger. It is probable that they sometimes extend a considerable way into the solid minerals.