CATALOGUE OF THE MECHANICAL ENGINEERING COLLECTION. 23 



the pencil, that above the atmospheric line records the steam pressure 

 during the forward stroke, and that below the line the vacuum pres- 

 sure during the return stroke. The area inclosed between the per- 

 pendicular lines and the lines made by the pencil is computed to find 

 the sum of the average steam and vacuum pressure to the square inch 

 of the piston within that section, and the result in pounds and decimal 

 parts placed below. The sum of these results is divided by ten to 

 find the average pressure on the piston during its forward and return 

 stroke. With this data, by quite simple rules the actual horsepower 

 required from the engine to do the work at the time the diagram was 

 taken is easily computed. 



There is also a friction diagram taken to show the power neces- 

 sary to run the engine and connecting machinery when not doing 

 work. Cat. No. 180,629 U.S.N.M. 



Print of James Watt's Steam Engine Indicator. 



In this indicator the rocking beam is discarded and the spiral 

 spring is placed above the piston, the cylinder being lengthened for 

 this purpose. A pencil is attached to the upper end of the piston 

 having an up and down motion only. The pencil rests upon a card 

 secured to a light frame that has a horizontal motion corresponding 

 to that of the piston in the engine's cylinder (though much less) 

 given to it by a cord and weight. Cat. No. 180,631 U.S.N.M. 



Prints from a Model of James Watt's Tilt Hammer. 



The beam of the engine has its reciprocating motion converted into 

 the rotary motion of a shaft by means of a connecting rod, crank, 

 or other device. On the shaft is a flywheel and the cams for lifting 

 the hammer. Two hammers are shown, one lifted by a cam under 

 the " belly " of the helve like an ordinarj^ forge hammer, except that 

 the helve of the hammer is parallel with the shaft. The other ham- 

 mer is lifted by another cam depressing the tail like an ordinary tilt 

 hammer. Cat. No. 180,624 U.S.N.M. 



Portion of Cylinder of a Jonathan Hornblower Steam Engine. Gift of the 

 New Jersey Historical Society. 



This cylinder is part of the first stem engine on the western con- 

 tinent, imported from England in 1753. Concerning it the Hon. 

 Joseph P. Bradley, Associate Justice of the Supreme Court of the 

 United States, wrote under date of September 20, 1875. 



The steam engine (of which this is a portion of the cylinder) was the first 

 ever erected on this continent. It was imported from England in the year 1753 

 by Col. John Schuyler for the purpose of pumping water from his copper mine 



