Question

Under what circumstances would it be more efficient for the circus owner, rather than the tamers themselves, to be liable for injuries to audience members? What is this principle called in Common Law?

Answer 1

Firrst of all , we need to distinguish between an employee and an independent contractor . Whether tamers in circus are employees or independent contractors is significant in fixing responsibilty for negligence done by them .

An employee is a person who performs work   under written or verbal contract and employer specifies what he's supposed to do the work and how it is to be done.

An independent contractor , however , is a person who is doing an independent trade , business, or profession in which their services to the public. The person who contracts or hires them for their services must have the right to control or direct the result of the work done, but not the ways or methods of doing that work.

Under common law doctrine of VICARIOUS LIABILTY , law imposes responsibilty upon one person for the failure of another , with whom the person has a special relationship ( particulary that of master and servant ) to exercise such care as a reasonably prudent person would use under similar circumstances. It's a legal doctrine that assigns liabilty for injury to a person who did not cause it but who has a legal relationship to the person who acted negligently. It is also referred as Imputed Negligence. Other theories of liabilty that are premised on imputed negligence include the RESPONDEANT SUPERIOR doctrine. The doctrine makes the master  responsible for negligence on part of the servant  in respect to whom he owed a duty of care. It also derives validity from the maxim QUI FACIT PER ALIUM FACIT PER SE , which means " he who does an act through another is deemed in law to do it himself".  For this doctrine to apply, the negligence should occur during the course of employment.

In case, of an independent contractor , are liable for any mistake done by them , not the employer.

The most popular way  to check whether the relationship is of employer - employee or employer- independent contractor is HIRE AND FIRE TEST, a person who employs another person and is his pay master, and has the power to fire ( discharge) him, is the master for the purpose of vicarious liabilty.