OBJECTS.] INTRODUCTORY. 29 



water is heavier than an empty tumbler, because the 

 full tumbler gives us a greater feeling of effort when 

 we lift it than the empty tumbler does. The more 

 water there is in the tumbler the greater is the effort. 

 A pail full of water requires still more effort, though 

 the empty pail feels quite light : and, when we come to 

 deal with a large tub full of water, we may be unable 

 to stir it, though the empty tub could be lifted with 

 ease. Thus it seems that the greater the bulk of 

 water the more it weighs, and the less the bulk the 

 less it weighs. But then a single drop of water in the 

 palm of the hand seems to weigh nothing at all. 

 However, this clearly cannot be, for the drop falls to 

 the ground readily, and therefore it must have weight. 

 Moreover, a few thousand drops would fill the tumbler, 

 and if a thousand drops weigh something, each drop 

 must have a thousandth of that weight. The fact is 

 that our feeling of effort is a very rough measure of 

 weight, and does not enable us to compare small 

 weights, or even to perceive them if they are very 

 small. To know anything accurately about weight 

 we must have recourse to an instrument which is 

 contrived for the purpose of measuring weights with 

 precision. 



21. The Measuring of Weights. The 

 Balance. 



Such an instrument is the balance or scales, which 

 you may see in every grocer's shop. It is composed 

 of a beam which moves easily on a pivot fixed to its 

 middle, and which has a scale-pan attached to each 

 end. So long as both scale-pans are empty the beam 

 is horizontal ; but if you put anything which has 



