Where can I find this book? Any ideas. Wiki doesn't give a location. The quest sounds interesting. Any help, thanks.

There's a copy on the floor in the ruins of the Hall of the Vigilants. That might be the easiest copy to find.

I found one in Fort Dawnguard, at the bottom of a bookcase on top of another book. The bookcase is completely empty except for those two books.

After Dawnguard, this book is almost everywhere I go...

It can also be found in a bookshelf in Dragonsreach,

Locations can be found http://uesp.net/wiki/Skyrim:The_Aetherium_Wars.