34 



with its axis in the bearings a, a' . The cylinder is revolved regularly 

 by the clock movement C. 



If the height of the mercurial column changes 1 inch, the rolling 

 carriage and recording pen will move 5 inches, thus giving a suffi- 

 cient magnification to render estimations of the pressure to the one- 

 thousandth part of an inch practicable. 



Figure 24. — Electric-motor mechanisms 



The portion of the long arm of the beam over which the rolling 

 carriage moves is provided with a scale of 20 subdivisions to the 

 inch, which represents hundredths of an inch of pressure. Still 

 further subdivision is effected by reference to the graduations on 

 the face of the notched wheel D. These represent the ten-thousandth 



