water by high degrees of force. 543 
register and disk, is to be inverted for experiment, as shown 
fig. 10. 
The piezometer so arranged was then placed in the receiver 
of the compressor, which was filled with water, and kept at 
a temperature of 50 degrees Fahrenheit. The steel pump 
C, was next screwed firmly into its upper end, which is \ an 
inch longer than the screw or body of the pump, entering a 
recess of the cylinder of the compressor, of about £ of an 
inch in depth, which it exactly fitted. Between the head of 
the pump and the bottom of the recess was placed a collar of 
lead, for the purpose of making a more perfect joint. 
The frame supporting the piston and pump handles was 
next screwed to the cylinder ; about \ an inch of the upper 
end of the pump was bell-mouthed, the better to receive the 
piston, which rises quite out of the pump. Two desirable 
objects are effected by the piston leaving the chamber at each 
stroke, viz. 1st. It allows the water to fill the pump in the 
simplest manner ; 2nd. The piston at each stroke receives a 
portion of .the oil, which floats on the surface of the water in 
the cup M, which is of great consequence in high pressure. 
The piston F, contracts as it enters the bell mouth of the 
pump, which, together with the pressure of the water against 
the interior of the piston, causes it to fit as perfectly as the 
leather cup in the barrel of an air pump. All being ready, 
the pump was set to work, and as soon as the intended pres- 
sure was known to be effected by use of the valve, the 
pressure was gradually taken off, by unscrewing the pump 
C. The piezometer being removed from the compressor, 
the indicating spring was found raised in the tube, more or 
less, according to the power employed. The greatest amount 
