What is the key case for ostensible authority?

Summers v Solomon - D owned a jeweller's shop. he employed a manager and as part of the role, they ordered jewellery for the shop. the manager left the role, and the plaintiff was employed. they believed that as part of their job, they had to order jewellery for the shop. D did not inform the plaintiff that he was taking away that part of the job and absconded the jewellery. the D was liable as he had not informed the plaintiff and the plaintiff was basing the job off previous authority.