LIBRA K Y 



UNIVERSITY OF 



CALIFORNIA. 





GENERAL PROPERTIES OF BODIES. 



1. Extension. Units. Determination of Volume. 

 When we examine the various bodies which surround us, 

 we find that, notwithstanding the many differences which 

 they exhibit, there are some properties which are com- 

 mon to all of them. The most obvious of these general 

 properties is extension in space. In most bodies this 

 property is perceived at once : a book, a block of wood, 

 and thousands of other objects possess length, breadth, 

 and thickness ; and these dimensions of a body in three 

 different directions constitute together its extension in 

 space. In some cases, instead of speaking of the breadth 

 of an object, we speak of its width ; or of its depth, 

 rather than of its thickness ; but there are always three 

 different dimensions, although it may sometimes appear 

 at first sight that a body has only one or two dimensions. 

 A sheet of tissue paper, or, better still, of gold leaf, has a 

 very appreciable length and breadth; but its thickness is 

 so small that special instruments are required to measure 

 and even to perceive it. But several hundred small 

 sheets of tissue paper placed one upon another and 

 slightly compressed, or a large sheet repeatedly folded, 

 would form a layer of measurable thickness : about 

 500 sheets of moderately fine tissue-paper are required 



B 



