﻿APPARATUS, 
  OR 
  MANIPULATION. 
  

  

  403 
  

  

  blished 
  between 
  the 
  cavities, 
  either 
  of 
  these 
  offices 
  may 
  be 
  performed, 
  

   accordingly 
  as 
  the 
  pressure 
  within 
  the 
  holder 
  is 
  made 
  greater, 
  or 
  less, 
  

   than 
  that 
  of 
  the 
  atmosphere. 
  It 
  will 
  be 
  greater 
  when 
  the 
  valve 
  for 
  

   the 
  admission 
  of 
  water 
  is 
  opened, 
  that 
  for 
  letting 
  it 
  out 
  being 
  shut 
  : 
  

   and 
  less 
  when 
  these 
  circumstances 
  are 
  reversed. 
  

  

  Fig. 
  1. 
  

  

  Fig. 
  2. 
  

  

  Fig. 
  2 
  affords 
  a 
  view 
  of 
  the 
  lower 
  side 
  of 
  the 
  

   sliding 
  shelf, 
  in 
  the 
  wood 
  of 
  which 
  it 
  will 
  be 
  

   seen 
  that 
  there 
  are 
  two 
  excavations, 
  converging 
  

   into 
  holes. 
  This 
  shelf 
  is 
  loaded 
  with 
  an 
  ingot 
  

   of 
  lead 
  at 
  L, 
  to 
  prevent 
  it 
  from 
  floating 
  in 
  the 
  water 
  of 
  the 
  cistern. 
  

  

  