32 SCIENCE PRIMERS. [MATERIAL 



proportion of its weight to its volume gives us the 

 density of a body. 



Now what is true of water is true of all other bodies 

 or material substances. Suppose that one of the 

 measures is emptied and replaced, the beam may be 

 brought to the horizontal position again by means of 

 a piece of lead cut to exactly the right size. The 

 piece of lead will thenceforth furnish an exactly cor- 

 responding or equivalent weight for so much water ; 

 and pieces of iron or brass, which counterpoise the 

 lead, will also be equivalents of the weight of the water, 

 or of the lead, or of one another. But the pieces of 

 lead, iron, or brass will obviously be of much less 

 volume or bulk than the water which they counterpoise. 

 Here it follows that the densities of these metals, or 

 the quantity of matter contained in the same volume, 

 must be much greater than in the case of water. 



What are called weights in commerce are pieces of 

 lead, or iron, or brass exactly equivalent in weight to a 

 certain bulk of water under certain conditions. An 

 imperial gallon of water thus weighs ten 

 pounds, and therefore an imperial pint 

 weighs a pound and a quarter. 



23. Equal Volumes of Different Things 

 under the same circumstances, have Different 

 Weights : the Density of Different Bodies is 

 Different. 



The important fact which has just been alluded to 

 must be considered more fully. We have seen that 

 an imperial pint measure gives us the space which is 

 taken up by as much water as weighs a pound and a 

 quarter ; and this space is the bulk or volume of that 



