Actually, the Coriollis effect has been debunked many times, by both FE'ers and RE'ers.
http://www.snopes.com/science/coriolis.asp
I would also question what the pendulum is hanging from. All rope is twisted, whether they be fibrous or steel. The weight of the pendulum will cause the rope to slowly unwind, and slight spinning can effect the direction the pendulum goes. When using twisted rope, the experimenter would need to note the direction the pendulum is turning, and if it is always in the opposite direction as the rope's twist. If it is always found to go in one direction according to twist, then the whole effect is nothing more than a parlor trick (magick) - and a very deceptive one at that.
The only way to truly test this would be to use a solid wire with no twist—and no swivel is needed because we're measuring the change in direction, not spin. For precise results the pendulum would need to be perfectly balanced—a tire balance can be used to determine if there are any heavy spots on any section along the diameter of the pendulum, and [precise weights] would be necessary to [true] the weight evenly. Repeat the experiment many times with different solid wires.
I suspect the experiment has always been done with twisted rope, never with solid wire, never with a balanced pendulum.