CALORIFICATION. 357 



The truth of this conclusion, is rendered 

 more apparent, when we reflect on the means 

 by which fire is factitiously and spontaneously 

 produced, while the union which takes place 

 between the solar rays and water is the cause s 

 of which gasification is the effect, the union 

 of the solar rays with opake matter, on the 

 contrary, is the cause of combustion. When 

 the solar rays are brought to a focal point in 

 pure water, they produce in it, a slight in- 

 crease in its temperature ; if a piece of wood, 

 however, be immersed in it, the difference is 

 obvious and striking; under circumstances 

 such as these, the wood has been actually 

 burnt and charred, and a great increase in the 

 temperature of the water produced. Although 

 the concentration of a lens, enables us to collect, 

 and to condense, an immense mass of rays, to 

 one point, so as to have the whole accumula- 

 tion within a very small compass; if that 

 point be in the air, no sensible effect is 

 produced; if, on the contrary, a solid sub- 

 stance be (exposed to its influence, fire the most 

 vivid and intense is the direct and immediate 

 consequence, and all the phenomena of ignition 

 and of combustion immediately follow. 



As the materials of which fire is com- 

 posed, are all referable to light and opake 

 matter, so the means by which it is produced, 

 are either chemical or mechanical, separately, 



