Lens of Observation

The three wizards sat in the deepest vault of the Wizard's Association headquarters, arrayed around a cramped table, with a small glass lens on a velvet cloth centered. The older one was gazing at the lens intently, while the other two looked visibly uncomfortable.
Alistair regarded the lens warily. "What the hell is this thing? It's warping the flow so bad I don't know if I can tap into it."
Mellitus picked the lens up and held it to the oil lamp. "This is the Lens of Observation, and the two of you are going to tap the flow by using the spellcraft I gave to you last week. If it works out, we won't have to lobotomize the both of you." The master of the Wizard's Association raised his hands. "Kidding. You're sworn to secrecy about this object, so don't go casually chatting about it."
Rigana folded her arms. "Well, it would only even make sense to wizards, so no point telling people that an eyepiece is making my skin crawl. What does it do?"
"It lets you observe." Mellitus stared into the Lens, and the other two wizards felt the flow of magic shift uncomfortably. "There's a latent that tracks you, Rigana. You were eating chocolate crepes this morning for breakfast."
Rigana's eyes widened. "What? How could you know that?"
Mellitus pointed at the lens. "Temporal and Spatial. Think about the spellcraft lines I gave you and line them up here. No need for hand or finger motions, use only the mind's eye." He handed the lens to Rigana. "See how it feels."
"What it feels like, is amazingly creepy. But alright." Alistair watched as Rigana held the lens in front of her. The flow changed, but this time much more noticably - she was pushing magic through the lens forcibly, and the resulting gusts of wind emanating from the lens made his eyes water.
"No, pull it back. Don't force it. You want to observe and follow the latent, not redirect it or create your own. Try again." Mellitus closed his eyes. "Do you feel the languid latent? Use that one. Don't force it, just let it flow, and follow the flow backwards."
Rigana stared at the lens intently, and the flow change was far less drastic on this attempt. She spoke softly. "This flow goes to the street, and down towards the outskirts. I can see the baker at Morrison's preparing her first batch of crepes for the day, from this morning." She blinked, and her eyes refocused on the room. "That was so vivid it felt like I was watching some sort of dream."
"Good. Alistair, you try." Mellitus placed the lens in Alistair's right hand, and he immediately felt the urge to clasp his hand shut - the lens felt wrong, the flow through it was so intense it could feel like his palm was burning. He shook his head and held the lens up, mentally drawing the spellcraft guide lines in and around the lens.
"I see the latents. Okay." Alistair picked a fast moving latent, unsteady because its natural flow was a mile away and was being forced through the lens unnaturally. "This one goes to....oh no. This one goes to the Scarlet Block." He blinked and glanced up, breaking his concentration. "Not joking, but I feel like I'm committing a crime of some sort if I go through with this."
Mellitus shook his head impatiently. "This is just between us. Go back in and finish the spell."
Alistair redrew the his guide lines and the lens quickly focused. "Alright. This is the Scarlet Block, around sunset, so a couple of hours ago. This is Madame Fleurise's establishment, a bedroom just above the entrance. Never been so that's only a guess, but this image is so strong I feel like I could have grown up in this room, as gross as that sounds. Okay. There's someone entering, an attractive courtesan, blonde, and...."
"Yes?" Mellitus folded his arms. 
"...Minister Tiessa. The civil service exam proctor. That old hag!" Alistair broke his concentration. "Right, so I can see why this is a secret object."

Mechanics & Inner Workings

The Observer Lens is, to a non-wizard, a simple magnifying glass lens in a brass housing. If presented to a wizard, however, the mind's eye sees the Lens for what it is - a locus point for natural magic flow, that draws the ambient flow into itself. The Lens has been subject to intensive research at the highest levels of state security, and it has been discovered that trained wizards can, with the Lens in augment, 'see' the history of the magical flow in the Lens. That is, a wizard can cast their mind's eye backwards along the latent both in time and in locale, allowing them to peer into the past into certain locations, at certain locations. 
Only certain wizards are capable of casting the complex magecraft needed to use the Lens, and of those, most are only capable of seeing 'back' a few hours. The most successful wizard, Archmagus Whelan, has successfully casted her mind's eye back two weeks, observing events across the continent, and she was able to accurately report the contents of text documents visible to her through the Lens, though thousands of miles away.

Significance

The Observer Lens is a magic artifact, one of the few discovered since the dawn of magecraft in 715, and is considered a state secret of the Principality of Etoile. The ability of remote observation, even if of past events, is considered destabilizing in the extreme, and a threat to the Principality, due to the potential for subterfuge and blackmail. Less than twenty in the Principality are aware of the existence of the Observer Lens, and all save the Princeps himself are sworn to absolute secrecy.
Prior to 715, the lens was part of the estate of one Lord Metier, whose possessions passed into the hands of the state upon his heir-less death in 694. It was only by sheer coincidence that a wizard felt something unusual whilst perusing the archives over twenty years later, and it is doubtful Metier had any idea of the import of his lens, or any record of its provenance.

Rarity

unique

Weight

2oz

Dimensions

roughly an inch square

Base Price

priceless

Raw materials & Components

The Observer Lens appears to be ordinary glass and brass, but is magically enhanced in a way that is unknown to the Wizard's Association of Etoile or the Principality.