They do stimulate the centre of physical sight, but not the astral; and that is why they cannot go very far.

You can get a certain amount of clairvoyance by these means, but you are only expanding your physical sight, and working on centres of the astral body connected with the physical organ of vision, the eye.

The true astral sight is an entirely different thing.

That comes from a centre of its own in the astral body.

It has to be created from the mental body, as the organ of the physical was from the astral.