65 



Tin sis causal l>y the animal, or concentrated vegetable gas, from 

 tin; body, reciprocating with tho mineral gas from the pipe. 



A light is often seen at the ends of branches of trees on a 

 xsool morning, resembling miniature auroras in appearance, this i 

 caused by the vegetable gas fron the tree, reciprocating with 

 the mineral atoms in the Air. 



The second and third divisions on the subject, viz : light 

 with heat and combustion, and how light is propagated, we will 

 'consider together. The explanation of daylight, we will reserve 

 For another chapter. 



Taking a candle tor our means of illustration, we find that 

 there are four things required to be looked at. 



First, the flame itself. 



Second) the heat from it, extending twelve inches or more all 

 around. 



Third, the light from it extending in a greater or less degree 

 for ten or twelve feet. 



Fourth, The phenomenon of the light itself, looked at from 

 a local distance of a few miles, according to the state of the 

 atmosphere. 



In the first, we burn our fingers if we put them in the flame. 



In the second, we feel warmth but we are not burnt. 



In the third, we do not feel the heat but the light is bright 

 enough to read by. 



In the fourth, we lose both heat and light, locally, and 

 can only see the flame as a distant object. 



The phenomena felt and observed in these four instances, 

 must of necessity make the action in each several case different 

 from the others. 



Now what is the action ? 



