along   channels   for   irrigation   and   domestic purposes, using dams and sluice gates to control the  flow.  The  ancient  Cretans  had  an  elaborate plumbing system. Archimedes studied the laws of floating   and   submerged   bodies.   The   Romans constructed  aqueducts  to  carry  water  to  their cities. After the breakup of the ancient world, there were few new developments for many centuries. Then,   over   a   comparatively   short   period, beginning near the end of the seventeenth century, Italian  physicist,  Evangelista  Torricelle,  French physicist,  Edme  Mariotte,  and  later,  Daniel Bernoulli  conducted  experiments  to  study  the elements  of  force  in  the  discharge  of  water through small openings in the sides of tanks and through  short  pipes.  During  the  same  period, Blaise Pascal, a French scientist, discovered the fundamental  law  for  the  science  of  hydraulics. Pascal’s law states that increase in pressure on the  surface  of  a  confined  fluid  is  transmitted undiminished throughout the confining vessel or system  (fig.  1-1).  (This  is  the  basic  principle  of hydraulics  and  is  covered  in  detail  in  chapter  2 of  this  manual.) For   Pascal’s   law   to   be   made   effective   for practical applications, it was necessary to have a piston that “fit exactly.” It was not until the latter part of the eighteenth century that methods were found to make these snugly fitted parts required in hydraulic systems. This was accomplished by the invention of machines that were used to cut and shape the necessary closely fitted parts and, particularly, by the development of gaskets and packings.  Since  that  time,  components  such  as valves,  pumps,  actuating  cylinders,  and  motors have  been  developed  and  refined  to  make hydraulics  one  of  the  leading  methods  of  trans- mitting  power. Figure 1-1.—Force transmitted through fluid. Use of Hydraulics The hydraulic press, invented by Englishman John   Brahmah,   was   one   of   the   first   work- able  pieces  of  machinery  developed  that  used hydraulics   in   its   operation.   It   consisted   of   a plunger pump piped to a large cylinder and a ram. This press found wide use in England because it provided a more effective and economical means of  applying  large  forces  in  industrial  uses. Today,  hydraulic  power  is  used  to  operate many  different  tools  and  mechanisms.  In  a garage,  a  mechanic  raises  the  end  of  an  auto- mobile with a hydraulic jack. Dentists and barbers use hydraulic power, through a few strokes of a control  lever,  to  lift  and  position  their  chairs  to a  convenient  working  height.  Hydraulic  doorstops keep  heavy  doors  from  slamming.  Hydraulic brakes  have  been  standard  equipment  on  auto- mobiles  since  the  1930s.  Most  automobiles  are equipped with automatic transmissions that are hydraulically  operated.  Power  steering  is  another application  of  hydraulic  power.  Construction workers  depend  upon  hydraulic  power  for  the operation   of   various   components   of   their equipment. For example, the blade of a bulldozer is  normally  operated  by  hydraulic  power. During  the  period  preceding  World  War  II, the  Navy  began  to  apply  hydraulics  to  naval mechanisms   extensively.   Since   then,   naval applications  have  increased  to  the  point  where many ingenious hydraulic devices are used in the solution of problems of gunnery, aeronautics, and navigation. Aboard ship, hydraulic power is used to operate such equipment as anchor windlasses, cranes, steering gear, remote control devices, and power drives for elevating and training guns and rocket launchers. Elevators on aircraft carriers use hydraulic  power  to  transfer  aircraft  from  the hangar  deck  to  the  flight  deck  and  vice  versa. Hydraulics  and  pneumatics  (chapter  11)  are combined  for  some  applications.  This  combina- tion  is  referred  to  as  hydropneumatics.  A n example  of  this  combination  is  the  lift  used  in garages   and   service   stations.   Air   pressure   is applied  to  the  surface  of  hydraulic  fluid  in  a reservoir.  The  air  pressure  forces  the  hydraulic fluid  to  raise  the  lift. STATES  OF  MATTER The  material  that  makes  up  the  universe  is known  as  matter.   Matter  is  defined  as  any substance  that  occupies  space  and  has  weight. 1-3