OBJECTS.] INTRODUCTORY. 33 



weight of water. But if you take an ordinary pound 

 weight and a quarter-pound weight, and put them into 

 an imperial pint measure, you will find that, instead of 

 filling it, they take up only a very small portion of the 

 space in its interior, or in other words, of its capacity. 

 Thus the volume of a pound and a quarter of lead, or 

 of iron, or of brass, is very much less than the volume 

 of the same weight of water ; that is to say, the metals 

 are denser than water ; the same volume has greater 

 mass or more gravity. Or, to put the case in another 

 way, fill the tumbler with which we began half full of 

 water, making a mark on the side exactly at the level 

 of the top of the water. Then place it in one scale of a 

 balance, and counterpoise it with weights in the other. 

 Next, pour out the water, and after drying the 

 tumbler, fill it with fine sand carefully up to the mark. 

 The volume of sand will be equal to the volume of 

 water. But now the same weights will no longer 

 counterpoise it, and you will have to put more 

 weights in the opposite scale. Volume for volume, 

 therefore, sand is heavier than water. Throw out the 

 sand, and put in sawdust in the same way, and you 

 will find that a less weight than was necessary to 

 counterpoise the water counterpoises the sawdust. 

 Volume for volume, therefore, sawdust is lighter than 

 water. Experiment in the same way with spirit and 

 oil, and they will be found to be lighter than water, 

 while treacle will be heavier, and quicksilver very 

 much heavier than water. 



24. The Meaning of Heavy and Light 

 Specific Gravity. 

 We are in the habit of using the words heavy and 



