Page:Various Forces of Matter.djvu/113

Rh and there it is burning under the water; and so it will continue until exhausted, and all by reason of the requisite amount of oxygen being contained within the substance. It is by this kind of attraction of the different particles one to the other that we are enabled to trace the laws of chemical affinity, and the wonderful variety of the exertions of these laws.

Now I want you to observe that one great exertion of this power which is known as chemical affinity is to produce and light; you know, as a matter of fact, no doubt, that when bodies burn they give out heat, but it is a curious thing that this heat does not continue—the heat goes away as soon as the action stops, and you see thereby that it depends upon the action during the time it is going on. It is not so with gravitation; this force is continuous, and is just as effective in making that lead press on the table as it was when it first fell there. Nothing occurs there which disappears when the action of falling is over; the pressure is upon the table, and will remain there until the lead is removed; whereas, in the action of chemical affinity to give light and heat, they go away immediately the action is over. This lamp seems to evolve heat and