It is useful, not only to study different countries with respect to their salubrity, but also to observe the different situations in the same locality, and the different quarters of the same city. M. Junod presented to the Academy of Sciences, some years since, an essay on this subject, which is full of interest. In considering the distribution of the population in large cities, we are struck by the tendency of the wealthy class to move toward the western portions, abandoning the opposite side to the industrial pursuits, It seems to have divined, by a kind of intuition, the locality which would have the greatest immunity in the time of sore public calamities. {79} For example, let us speak first of Paris. From the foundation of the city, the opulent class has constantly directed its course toward the west. It is the same in London, and generally, in all the cities of England. At Vienna, Berlin, St. Petersburg, and, indeed, in all the capitals of Europe, this same fact is repeated; there is the same movement of the rich toward the west, where are assembled the palaces of the kings, and the dwellings for which only pleasant and healthy sites are desired. In visiting the ruins of Pompeii and other ancient cities, I have observed, as well as M. Junod, that this custom dates from the highest antiquity. In those cities, as is seen at Paris in our day, the largest cemeteries are found in the eastern parts, and generally none in the western. M. Junod, examining the reason of so general a fact, thinks it is connected with _atmospheric pressure_. When the mercury in the barometer rises, the smoke and injurious emanations are quickly dispelled in the air. When the mercury lowers, we see the smoke and noxious vapors remain in the apartments and near the surface of the earth. Now every one knows that, of all winds, that from the east causes the mercury in the barometer to rise the highest, and that which lowers it most is from the west. When the latter blows, it carries with it all the deleterious gases it meets in its course from the west. The result is, that the inhabitants of the eastern parts of a city not only have their own smoke and miasmas, but also those of the western parts, brought by the west wind. When, on the contrary, the east wind blows, it purifies the air by causing the injurious emanations to rise, so that they cannot be thrown back upon the west. It is evident, then, that the inhabitants of the western parts receive pure air from whatever quarter of the horizon it comes. We will add, that the west wind is most prevalent, and the west end receives it all fresh from the country.