Let us next consider the causes of high temperature in the city of New York. It is a well-established fact that the temperature of large and densely populated towns is far higher than the surrounding country. This is due to a variety of causes, the chief of which are the absence of vegetation; the drainage and hence the dryness of the soil; the covering of the earth with stone, bricks, and mortar; the aggregation of population to surface area; the massing together of buildings; and the artificial heat of workshops and manufactories. The difference between the mean temperature of the city at Cooper Institute and at the Arsenal, Central Park, for a single month, illustrates this fact. Another striking difference between the temperature of these two points of observation is that the range is much greater at Central Park than at Cooper Institute, the temperature falling at night more at the former than at the latter place. The effect of vegetation is to lower the temperature at night, while brick and stone retain the heat and prevent any considerable fall of temperature during the twenty-four hours. It may be said of New York that it has all the conditions of increased temperature above given in an intensified form. It has a southern exposure; all of its broad avenues run north and south; the surface is covered with stone, brick, and asphalt; it is destitute of vegetation except in its parks, which have a very limited area compared with the needs of the city; its buildings are irregularly arranged and crowded together so as to give the largest amount of elevation with the least superficial area; ventilation of courts, areas, and living rooms is sacrificed; its ill-constructed and overcrowded tenement houses, especially of certain districts, have the largest population to surface area of any city in the civilized world. To these natural and structural unfavorable sanitary conditions must be added the enormous production of artificial heat in dwellings. When the summer temperature begins to rise the solar heat is constantly added to the artificial heat already existing. The temperature of the whole vast mass of stones, bricks, mortar, and asphalt gradually increases, with no other mitigation or modification than that caused by the inconstant winds and occasional rainstorms. And the evils of high temperature are yearly increasing as the area of brick, stone, and asphalt extends. The records of sunstroke during the past few years is appalling, both on account of the number of cases and their comparative increase. If no adequate remedy is discovered and applied, the day would not seem to be distant when the resident, especially if he is a laborer, will remain in the city and pursue his work during the summer at the constant risk of his life.