MECHANICS AND USEFUL ARTS. 33 



great cross-head, or cap, which is furnished with a guide-rod, or spin- 

 dle ; both pistons and cross-head are fitted with iron plates, and 

 together, with parts of the engine attached, have an effective weight 

 of nearly 90 tons. The Engine House is a circular tower, on the 

 walls of which are arranged 1 1 large cast-iron balance-beams, which 

 radiate from the centre of the engine. Their inner ends, furnished 

 with rollers, are brought under the circular body of the great cap, 

 and their outer ends are connected to the pistons of 11 pumps of 63 

 inches diameter each; the stroke of both ends is 10 feet; and the 

 discharge from the pumps 66 cubic metres, or tons, of water per stroke. 



The action of the engine is very simple ; it is on the high-pressure- 

 expansive-condensing principle. The steam is admitted first beneath 

 the small piston ; and the dead weight of 90 tons is lifted, carrying 

 with it the inner end of the pump balances, and of course allowing 

 the pistons to descend in the pumps. 



The equilibrium valve then opens, and the steam in the cylinders 

 passes round to the upper surface of the small and annular pistons ; 

 puts the former in a state of equilibrium, and presses with two-thirds 

 of its force upon the annular piston, beneath which a vacuum is 

 alwavs maintained : thus, the down stroke of the engine, and the eleva- 



* O 1 



tion of the pump pistons and water, is produced by the joint action of 

 the descending dead weight in the cap and pistons, and the pressure 

 of steam on the annular piston. The engine has two air pumps, of 40 

 inches diameter, and 5 feet stroke each. The water is lifted by the 

 pumps into the canal, from which it passes off towards the sea sluices. 



The total weight of iron employed for the engine, pumps, &c., is 

 640 tons. The cost of the machinery and buildings, 36,000. 



The pumping was actively commenced in May, 1848, and has been 

 continuously carried on up to the present time. The Lake is now 

 nearly dry ; much of the bottom is exposed, only large pools of water 

 being left. The remains of the unhappy village of Nieuweinkirk have 

 been found, with a mass of human bones, on the very spot where the 

 old charts of the province fixed its site. From May, 1848, up to 

 April, 1851, the Lake was lowered 7 feet 3 inches. The level reached 

 at the end of October of the same year was 9 feet 7 inches below the 

 original surface, or at an average rate of 4.79 inches per month. In 

 November, 1851, a great quantity of snow and rain fell, raising the 

 level of the Lake about four inches, and in December the weather 

 was still unfavorable, so that at the end of that month, the level stood 

 at 9 feet 5.38 inches below the original surface, showing a total gain 

 since April of 2 feet 5.58 inches, or 3.32 inches per month. This pro- 

 gress may appear to some inconsiderable ; but when it is recollected 

 that the lowering of the Lake one inch involved the raising of up- 

 wards of 4,000,000 of tons of water, and allowing f jr rain and snow 

 falling during these eight months, there could not have been less than 

 186,000,000 tons of water pumped up during that period, the per- 

 formance will appear great indeed. To give a better idea of this, it is 

 stated that 186,000,000 tons of water are equal to a mass of solid rock, 

 one mile square, and 100 feet high, allowing 15 cubic feet to a ton. 



