Under the division of this volume devoted to “air and vacuum pumps,” much information has been given relating to the principles of the condensation of steam and also some illustrations of working machines. Still it may be well to say this, in addition, that—
All questions in regard to a vacuum become plain when we consider that the atmosphere itself exerts a pressure of nearly 15 pounds, and measure everything from an absolute zero, 15 pounds below the atmospheric pressure. We live at the bottom of an ocean of air. The winds are its currents; we can heat it, cool it, breathe and handle it, weigh it, and pump it as we would water. The depth of this atmospheric ocean cannot be determined as positively as could one of liquid, for the air is elastic and expands as the pressure decreases in the upper layers. Its depth is variously estimated at from 20 to 212 miles. We can, however, determine very simply how much pressure it exerts per square inch.
UTILITIES AND
ATTACHMENTS
Working Ship Pumps by Ropes.
UTILITIES AND ATTACHMENTS.
Utility is a Latin word meaning the same as the Saxon word usefulness, hence a utility is something to be used to advantage.