Where is "volume" in world in blender 2.78? I have Belender 2.78 and am trying to create fog in the world. Plenty of tuts on YouTube saying to go to World, then Volume, then add Volume Scatter. Only one problem. There isn't a "Volume" in World. In Blener Render or Cycles Render (and I'm using cycles).  

Here is what's available under World, in this order:

*Custom Properties
*Preview
*Surface
*Ambient Occlusion
*Ray Visibility
*Settings

2.78 manual shows Volume in the list for World. Do I have a glitch copy?
Under surface, press "use nodes" and then instead of the surface being set to background, change it to volume scatter.