366 CALORIFICATION. 



compound) be examined, they will be found 

 to be totally different, from those of its 

 elementary parts ; instead of the fire radiating* 

 from a point, to an indefinite extent, its power 

 of motion becomes more limited and bounded, 

 in consequence of the resistance to which it is 

 exposed : and, instead of the water continuing 1 

 incompressible as before, it acquires an expan- 

 sible power, to a very great extent. At the 

 point of ebullition, the dilatation which it then 

 undergoes, suddenly increases in a greater de- 

 gree, than the augmentation of the fire could 

 be supposed capable of producing. Mr. GRE- 

 GORY very properly observes, that there is a 

 very considerable difference in the result of ex- 

 periments, performed with a view of determin- 

 ing the ratio, between the densities of water, 

 and the vapor of water at the boiling point ; 

 while Mr. HENRY states it to be as 1728 to 1 ; 

 others have carried it as far as 2, and even 3,000 

 times its original bulk. However varied the pro- 

 portion may be, the fact is universally admitted, 

 the power which vapor possesses of pressing 

 upon surrounding bodies, and of overcoming 

 their resistance, is familiar to every one. The 

 celebrated Engineer, VAUBAN, has observed, 

 that while 140lbs. of gunpowder, can only ex- 

 plode and overcome the resistance of 30,000 

 weight; 140 Ibs. of water, converted into va- 



