Of course, the problem now is finding a way to get Childermass over to the puddle. Strange doubts he can simply say something like 'Childermass, come look at this interesting puddle I found!'. He needs an excuse, he needs to lie, and he needs to sell the lie to Childermass, each of which seems exponentially more difficult the more he thinks about it.

"Perhaps this is a sign that I shouldn't use fire in my act." There's a pause, as Strange looks around the room, eyes lighting on the puddle as if he's spotted it for the first time. "At least with water, the most someone can get is wet."

Strange idly walks over towards the puddle as he sends the water up in the air, making the puddle into a small fountain for a moment or two. "I'd need more water, though. The most you could use something like this for is peering in on someone."

Wait. That might work. It's apparent from Strange's face that he's planning something, but what it is, Childermass couldn't tell. If he could convince Childermass that his magic could somehow peer back in on London, that might draw him over. After all, at least in Strange's time, Norrell's still being a busybody all around London. Surely Childermass would want to see what his employer was up to, right? Maybe? It's the barest hint of a plan but it would at least get Childermass over here. And hey, he couldn't peer back into London using a spell for seeing where a specific person was, but if he tried a different spell, maybe there would be different results! He'd lure Childermass over here and learn more about faerie's limitations on his magic, two birds with one stone!

A look of wild glee on his face, Strange turns towards some of the scattered straw he was using earlier and starts rummaging through it, as if searching for something specific among the straw.

Of course, nowhere in Strange's mind has he taken into account that the plan might not work.