I have just realized there are two ways to produce volumetrics in the new 2.7:
a) Create an object (cube) and apply the volumetrics to that object - it becomes a block of air. I can do this in nodes using the volume scatter shader.
b) Apply the Volume Scatter to the world.
I am trying to follow a tutorial on this second method but have run into a problem where my Blender 2.7 does not match his. He changes a “Device” setting from GPU to CPU, but I can find no such setting (see photo). Whether I try to follow his steps or try to attach the Volume Scatter shader to the volume port of the world output node, my screen is just black.
His tutorial: http://www.blenderguru.com/tutorials/make-atmospheric-lighting-blender/#.U6He253n-gg
Thanks for any clues.