" The opportunity of ascertaining the temperature of the earth at great depths was not neglected during the progress of the works at Grenelle. Thermometers placed at a depth of thirty yards in the wells of the Paris Observatory invariably stand at 53 Fahrenheit. In the well at Grenelle the thermometer was 74 at a depth of four hundred and forty-two yards, and at five hundred and fifty yards it stood at 79. The depth attained

PRELIMINARY ESSAY. 69

being six hundred and two yards, the temperature of the water which rose to the surface was 81, corroborating previous calculations on the subject. Now that the patient labor of so many years is brought to a close, the neighbors regret that it was not necessary to go to a depth of about one thousand yards for a supply, as the water would then have been at a temperature of 104, and immediately applicable to bathing establishments and other

places in which warm water is required."

THE AaUEDUCT OF LISBON. The aqueduct of Lisbon has been long admired for the excellence of its construction, and, in point of magnitude, is not inferior to any similar edifice which the ancients have

left us. That part of it situated in the valley of Alcantara, about a mile from Lisbon, consists of thirty-five arches, by which the water is conveyed over a deep vale, formed by

two opposite mountains. The dimensions of it in the deepest part of the valley are as follows height of the arch from the ground to the intrados, 230 feet, 10 inches from : ;