6b SCIENTIFIC RECREATIONS. 



Water is the means by which the Specific Gravity of liquids or solids is 

 found, and by it we can determine the relative densities of matter in propor- 

 tion. Air is the standard for gases and vapours. Let us examine this, and 

 see what is meant by SPECIFIC GRAVITY. 



We have already mentioned the difference existing between two equal 

 volumes of different substances, and their weight, which proves that they 

 may contain a different number of atqms in the same space. We also know, 

 from the principle of Archimedes, that if a body be immersed in a fluid, a 



Fig. 70. Deception jugs of old pattern. 



portion of its weight will be sustained by the fluid equal to the weight of the 

 fluid displaced. 



[This theorem is easily proved by filling a bucket with water, and moving 

 it about in water, when it will be easy to lift; and likewise the human body 

 may be easily sustained in water by a finger under the chin.] 



The manner in which Archimedes discovered the displacement of liquids 

 is well known, but is always interesting. King Hiero, of Syracuse, ordered 

 3, crown of gold to be made, and when it had been completed and delivered 



