Indeed, the second pic is a magnification of the first.
These are eriophyid mites. You can find quite a lot of information about them online, but the important point is that, while considered a harmful insect, they rarely do any significant damage to a tree. Trees can support huge populations of these little critters, and be none the worse for the wear. Their presence is usually more of a problem of aesthetics to the tree owner, rather than to the health of the tree. Pesticides are considered "overkill", and treatment in general is just to keep the tree well watered and fertilized, perhaps with a mulch of compost.
I found a few good sites about them, if you are interested. I think the first one is the best, and among others, it offers information about the one you have on your tree. There are many, many species of these mites, though, and they show up in different ways, i.e. galls, rusts, blisters, etc.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams