86 Domestic Science 



lamp chimney, and calculate the volume of the portion 

 of the chimney immersed when the plate falls off in 

 each determination made. This volume also represents 

 approximately that of the water displaced by the 

 apparatus at the instant the plate falls, if we neglect 

 the amount displaced by the cork and disc. Since 

 1 c.c. of water weighs 1 gram, the weight of water 

 displaced in each case is easily found. Compare these 

 weights with the total weight of the disc, etc. used in 

 the corresponding determination, and it will be noticed 

 that, allowing for errors of experiment, the weight of 

 water displaced is equal to the total pressure in each 

 case. 



For the above experiment there can be no pressure 

 of the water in an up and down direction on the vertical 

 walls of the lamp chimney. The whole upward pressure 

 of the water on the immersed body is therefore that 

 which we have measured on the horizontal disc. The 

 results which we have found may be proved to be true 

 in all cases, namely, that : 



(a) The pressure on a surface immersed in a 

 fluid varies directly with the depth of immersion ; 



(6) The total upward pressure of a fluid on an 

 immersed body of any shape is equal to the weight of 

 the fluid displaced by the body. 



The cylinder closed with a disc has been chosen for 

 experiment because it has only vertical sides and a 

 bottom surface ; in the case of a fully immersed body 

 with a top surface also under water, the total upward 

 pressure is the difference between the upward pressure 

 on the bottom surface and the downward pressure on 

 the top surface. Since the top surface is at a less 

 depth than the bottom surface, by (a) above the 

 downward pressure on the top is less than the upward 



