"Scientists are now venturing into what are the subtler planes of matter, and therefore into the realms of the unproven, and we should remember that, until recently, science has refused to admit their existence. We are passing beyond the sphere of what has been called "solid matter," into such realms as are inferred when we speak about "centres of energy," "negative and positive force," and "electrical phenomena"; and the emphasis is being laid more and more upon quality rather than upon what has been called substance."