and six feet in depth, to which the race is excavated below the overfall of the dam, and of course, room is allowed for a continual passage of four hundred and eighty square feet of water ; these arches are on the north of the race, and the mill buildings being on the west, the water passes from the race to the wheels which discharge the water. The mill buildings are of stone, two hundred and thirty-eight feet long and fifty-six feet wide ; the lower section is divided into twelve apartments, four of which are intended for eight double forcing pumps ; the other apartments are for the forebags leading to the water wheels. The pump and forebag chambers are arched with brick, and are perfectly secure from the inclemency of the weather. Those now in use, are kept warm by means of two large iron stoves, heated to great advantage and economy with Schuylkill and Lehigh coal. It has been from the commencement determined, for the present, to erect only three wheels and pumps, which are now completed, and with them the most important parts of the duty of the committee. The first of the wheels is fifteen feet in diameter and fifteen feet long, working under one foot head and seven feet fall. This was put in 20 78 PRELIMINARY ESSAY. operation on the 1st of July, 1822, and it raises one and a quarter million of gallons of water to the reservoir in twenty -four hours, with a stroke of the pump of four and a half feet, a diameter of sixteen inches, and the wheel making eleven and a half revolutions in a minute. The second wheel was put in operation on the 14th of September, and is the same length of the first, and is sixteen feet in diameter ; it works under one foot head and seven and a half feet fall, making thirteen revolutions in a minute, with a four and a half feet stroke of the pump, and raises one and one third million of gallons in twenty-four hours. The third wheel went into operation on the 24th December, 1822, and is of the same size as the second, and works under the same head and fall, making thirteen revolu- tions in a minute with a five feet stroke of the pump, and raises one and a half million gallons of water in twenty-four hours. It is not doubted that the second wheel can be made to raise an equal quantity, thus making the whole supply upwards of four millions of gallons in twenty-four hours. The wheels are formed of wood, and put together with great strength ; the shafts are of iron, weighing about five tons each. The great size and weight of the wheel give it a momentum which adds greatly to the regularity of its motion, so necessary to preserve the pumps from injury under so heavy a head as they are required to work, which is a weight of 7,900 Ibs., the height ninety-two feet. " The pumps are placed horizontally, according to a design of Mr. F. Graff, and are worked by a crank on the water wheel ; they are fed under a natural head of water, from the forebags of the water wheel, and are calculated for a six feet stroke ; but hitherto it has been found more practicable to work with not more than five feet. They are double forcing pumps and are connected, each of them, to an iron main of sixteen inches diameter, which is carried along the bottom of the race to the rock at the foot of Fairmount, and thence up the bank into the new reservoir. At the end of the pipe there is a stop-cock, which is closed when needful for any purpose. The shortest of these mains is two hundred and eighty-four feet long ; the other two are somewhat longer. The reservoir next the bank is one hundred and thirty-nine feet by three hundred and sixty feet, is twelve feet deep, and contains three million of gallons ; it is connected at the bottom with the old reservoirs by two pipes of twenty inches diameter with stop cocks. This reservoir contains four millons of gallons. All the water, being raised into the reservoirs one hundred and two feet above low tide, fifty-six feet above the highest ground in the city, is thence conveyed to the city, by iron pipes." On 24th October, 1822, the steam engines of the old work were stopped, never again, we presume, to be wanted. The actual consumption of water in Philadelphia, is stated at 2,000,000 gallons in winter, and 3,000,000 in summer, " when the streets are washed." PRELIMINARY ESSAY. 79 The distribution of the water from Fairmount, is