The Thaumometer allows you to scan things (blocks, items, mobs, nodes, etc.) to identify their aspects, collect Research Points, and unlock research. Looking through them also allows you to see aura nodes. Once something is scanned, viewing it through the Thaumometer will display not only its aspects, but its name, including the "type" of nodes.
Later, the Goggles of Revealing will provide continuous "auravision", but the Goggles can't give you research points, nor identify things by name.
This thaumometer is one of the most useful and important tools in a thaumaturgists arsenal, second only to the wand.
Firstly it allows you to scan objects, creatures or mystical phenomena and determine their magical make-up. You simply need to hold the right mouse button and wait.
Secondly it makes discovering nodes easier, as they become clearly visible if viewed through the Thaumometer's lens - even through solid objects!