396 Water in tie State of Ice. [Book VII. 



is left empty. The fleam which is above the pifton, 

 ceafmg to be counteracted by that which is below it, 

 acts upon the pifton HH, and forces it to defcend to 

 the bottom of the cylinder, and ib raifes the bucket 

 of the pump by means of the lever. The paffage K 

 between the inner cylinder and the condenfrr is then 

 Unit, and another paflage O is opened, which permits 

 the fteam to pafs from the outer cylinder, or from the 

 boiler into the inner cylinder under the pifton ; and 

 then the fuperior weight of the bucket and pump rods 

 pulls down the outer end of the lever or great beam, 

 and raifes the pifton, which is fufpended to the inner 

 nd of the fame beam. 



When water is expofed to a cold atmofphere, it 

 firft lofes its free caloric, and is reduced in tempera- 

 ture, but no part of it begins to freeze till the mate 

 is reduced fomewhat below the thirty-fecond degree 

 of Fahrenheit's thermometer ; a fmall quantity of the 

 water then becomes folid, which, by changing its 

 ftate, fets at liberty a quantity of its combined heat, 

 which reftores the water in contact with it to the 

 temperature of 32 degrees, or rather above it. The 

 congelation is therefore at a ftand till this -fenfible 

 heat is abftracted by the atmofphere, and the mafs 

 again reduced fomewhat below the thirty-fecond de- 

 gree. Another portion of water then congeals, and 

 the procefs is again flopped by the emiffion of heat. 

 In this manner congelation pervades the whole mafs, 

 and is performed at intervals, which are very ob- 

 fervable when the phenomenon of freezing is accurately 

 attended to. 



The fame law operates in the pafiage of other bodies 

 from the ft.ite of fluids to that of folids, and the contrary. 

 Dr. Irvine has mewh, that when fpermaceti and wax are 

 melted, they contain the matter of heat in a combined 



