44 IN STARRY REALMS. 



respiration is a necessity. Animals absorb the oxygen 

 and give off carbonic acid, while plants remove this gas, 

 which is pernicious to animal life, abstract from it the 

 carbon they want, and restore the invigorating oxygen. 



Thus the growing tree absorbs heat from the sunbeams, 

 and is enabled to acquire from the air that quantity of 

 carbon which is essential for its increase. Afterwards, 

 when the tree is burned in the fire, the carbon returns 

 again to carbonic acid, and in doing so radiates forth again 

 the heat which had been absorbed in its manufacture. 



This process becomes particularly interesting when 

 viewed in connection with our supply of fuel in the form 

 of coal. It is well known that coal is the remains of a 

 splendid vegetation, which from time to time has been 

 permitted to clothe large tracts on our globe. No one can 

 venture to express the thousands of years or the millions 

 of years that have elapsed since the last coal forests 

 flourished. Certain it is that the period was long ere man 

 came on this globe. The sun must have shone in those 

 ancient days as he does at present. His genial beams 

 were not, however, lost even so far as man was concerned. 

 The leaves on the great carboniferous forests captured 

 those beams, utilised them on a stupendous scale for the 

 production of carbon, and thus manufactured mighty seams 

 of coal. When we now put this coal on our fires, the heat 

 which it discharges is none other than that sun heat which 

 was laid by in the time of those primeval forests. The 

 light from our gas-burners is of course directly derived 

 from coal, but we may speak of it really as well as figura- 

 tively as artificial sunshine ; indeed, we might even go 

 further, and show that almost every spurce of Jieat and 



