480 



NEGEETTI AND ZAMBEA, HOLBORN VIADUCT, B.C., 



2940 Working Model of Bramah's Hydrostatic Press, s. a. 



raising 400 Ibs., brightly finished^ with keys and 

 breaking irons complete (fig. 2940) . . . . 12 12 



2941 Model of Undershot Wheel 



2942 Model of Overshot Wheel 



2943 Model of Breast Wheel 



2944 Model Canal Lock and Sluice Gates . . from 



2945 Current Meters, for showing the Rate or Flow of Tide in 



a Stream or River, and the amount of gallons per hour 

 delivered (see also page 299, No. 1190) 



Nos. 2941 to 2944, made to order. 



18 18 

 4 4 

 4 4 

 4 4 



10 10 



660 770 



HYDROMETERS, SACCHAROMETERS, GRAVIMETERS, ETC., FOR DETERMINING THE 

 SPECIFIC GRAVITY OF FLUIDS AND SOLIDS (SEE PAGES 176 TO 195) 



HYDRAULIC PRESSURE GAUGES (SEE PAGES 205 TO 209). 



WATER PRESSURE. 

 Pounds per Square IncTi, at Different Heights. 



Each 33 feet vertical height of water equals one atmosphere, or 15 Ibs. nearly. 

 In Sea Water sp. gr. 1'027, the pressure in descending increases at the rate of 280 Ibs. 

 upon the square inch for every 100 fathoms, or exactly 1 ton for every 800 fathoms. 



ATMOSPHERIC PRESSURE. 



Pascal's celebrated experiment was made at Rouen in 1646. He took a tube of nearly 

 50 feet long, closed at one end, and having filled it with water, placed it vertical with the 

 open end in a vessel of water, 'and found that a column of water was supported in the tube 

 of 34 feet long, and is 13'6 times higher than the mercury. 



Mercury being 13 f 9 times heavier than water, the weight of this column of water was 

 exactly equal to that of the mercury in Toricelli's experiment, and consequently it was the 

 same force, viz., the pressure of the atmosphere, which supported the two fluids. 



Assuming that the tube in Pascal's experiment is equal to a square inch in sectional 

 area, and that the height of the mercurial column is 30 inches, this column will contain 

 30 cubic inches ; and as a cubic inch of mercury weighs 3433-5 grains, or 0'49 of a pound, 

 the pressure of this column on a square inch of surface will be found to be 14*7 pounds. 

 The pressure of the atmosphere is in round numbers taken at 15 Ibs. on the square inch. 

 The pressure upon a square foot of surface containing 144 square inches is equivalent to 

 2,160 Ibs., or very nearly 1 ton. The surface of a man's body of average size is equal to 

 about 16 square feet ; the pressure therefore exerted upon this area, 37,560 Ibs., or upwards 

 of 16 tons. 



Air is 813*67 times lighter than water. 



