96 HYDROSTATICS. 



ally to differ in different latitudes, provided it be 

 taken up at a sufficient depth. 



Salt Water Ice. 



When salt water ice floats in the sea at the freezing 

 temperature, the proportion above to that below the 

 surface is as one to four nearly ; and in fresh water 

 ice at the freezing point as one to seven, supposing 

 the base under water does not spread beyond that 

 above water. 



Expansion of Spirits. 



Spirits expand and become lighter by means of 

 heat, in a greater proportion than water, they are 

 consequently heaviest in winter. A cubic inch of 

 brandy has been found by many experiments to weigh 

 ten grains more in winter than in summer, the diffe- 

 rence being between 4 drachms 32 grains, and 4 

 drachms 42 grains. Liquor merchants take advan- 

 tage of this circumstance, making their purchases in 

 winter rather than in summer, because they get in 

 reality rather a larger quantity in the same bulk, 

 buying by measure. 



Pressure of Water by height. 



The pressure of water is not in proportion to its 

 bulk, but only to the height at which it stands, so 

 that a long small pipe containing a pound or two of 

 water, will give the pressure of 20 or 30 tons : in- 

 deed twice or thrice as much, if its length be increased 

 and its bore lessened, without the least regard to the 

 quantity of liquid. 



