Lambert's estimation of Childermass's current facilities is much lower than the magician's, but he'll at least stop shoving at him (after a final firm press of his hands to drive the point home -- stay fucking put). He doesn't move far after he's let him go, and there's the rustle of paper and the scratch of a pen again, louder here now that they aren't outdoors.

When he's finished, Lambert presses the folded paper into Childermass's palm, using his other hand to close the magician's fingers over it. Depending on how much his eyesight will allow him to make out, if he unfolds the paper he'll find a simple message intended for whoever happens across him.

Something's wrong with his eyes, went to find out if it can be fixed. Don't let him do anything stupid. - Lambert

Lambert releases Childermass and steps towards the entrance again, the flap of cloth and his blurring figure -- framed for a moment by daylight -- announcing his exit.