The Constitution of Matter 71 



a suitable weight, say one -half the value of the greatest 

 weight shown on the scale of the balance, from the 

 lower end of the instrument and note the reading of 

 the indicator on the scale. Describe the new shape 

 taken up by the spring. Attach the upper end of the 

 balance to a support and allow the weight to hang 

 from it for a quarter of an hour. Take readings of the 

 position of the indicator every three minutes. With 

 a well-made spring, no measurable alteration of the 

 reading will be noted. Measure the increase in length 

 of the spring due to the attachment of the weight. 

 Repeat the experiment, using another weight. Note 

 the relation between the increase of length caused in 

 this case and that caused by the former weight, and 

 compare it with the ratio between the weights used. 



In this experiment, the spring is changed in shape 

 by the action of a force, the amount of change is 

 definite for a given force and does not alter appreciably 

 when the time during which the force acts is prolonged. 

 Further, the amount of change produced is directly 

 proportional to the force producing it. 



In common with all other bodies, solids have 

 definite masses, as already indicated in a previous 

 chapter. The chief characteristics of a solid body may 

 be summarised thus : 



It has a definite mass ; it retains its shape with- 

 out lateral support ; its volume and shape are in 

 general not easily altered except by the action of 

 a considerable force ; when its shape is changed under 

 the action of a force, the change produced is definite 

 and dependent upon the force applied. 



42. Let us next examine the qualities of a liquid. 



EXPERIMENT 23. Half fill a small flask with water 

 and cork it securely. Gum a strip of paper to the 



