How does Mrs Hall respond to the stranger?

Respond to? Please be more specific. His presence? Something he says or does?

Mrs. Hall was uneasy with the stranger, though she could not put her finger on the reason. She was impressed by his vocation.....

"I should explain," he added, "what I was really too cold and fatigued to do before, that I am an experimental investigator."

"Indeed, sir," said Mrs. Hall, much impressed."

and she was sympathetic to his physical complaints....

"—necessitates a certain retirement. My eyes—are sometimes so weak and painful that I have to shut myself up in the dark for hours together. Lock myself up. Sometimes—now and then. Not at present, certainly. At such times the slightest disturbance, the entry of a stranger into the room, is a source of excruciating annoyance to me—it is well these things should be understood."

"Certainly, sir," said Mrs. Hall. "And if I might make so bold as to ask—"

"That I think, is all," said the stranger, with that quietly irresistible air of finality he could assume at will. Mrs. Hall reserved her question and sympathy for a better occasion.