198 PHYSIOLOGICAL PHYSICS. [Chap. xix. 



on the tube. In the other pan of the balance counter- 

 poise with weights the flask with water a,nd the body. 

 Then remove the flask and place the body inside of it. 

 It will displace from the flask a quantity of water 

 equal to its own volume. Carefully dry the flask, see 

 that the water is at the same level as before, and 

 weigh it again. This time the weights in the opposite 

 pan . will be too much, because a certain amount of 

 water has been displaced. The diminution in weight, 

 consequently, will indicate the weight of water dis- 

 placed by the body, that is, the weight of a mass of 

 water whose volume is equal to the volume of the 

 body. Let this diminution be represented by 2-5. The 

 original weight of the body was 10, the weight of a 



quantity of water of equal volume is 2-5, then 9> = 



4 the specific gravity of the body. 



Similarly the specific gravity of a liquid could be 

 obtained. This requires a flask, the upper part of 

 which is drawn out into a fine tube. The flask is 

 placed in a balance and counterpoised. It is then 

 filled with water up to a mark on the fine tube. The 

 additional weights required give the weight of the 

 water. The water is then removed and the liquid 

 placed in the flask up to the same mark, and the weights 

 it requires determined. Thus, the weights of equal 

 volumes of water and of the liquid are obtained, and the 

 latter divided by the former gives the specific gravity. 



The principle of Archimedes indicates other methods 

 for readily determining the specific gravity. 



The hydrostatic Imlawce is one of these 

 methods. Any ordinary balance will suit the 

 purpose. Let it be raised on a stand, and suspend 

 by a thread, or fine wire, from 0118 of the pans the 

 body whose sp. gr. is to be measured. Counter- 

 poise with weights in the other pan, and so find 

 the weight of the body in air. Then, under the pan 



