The Light-Bearing Ether

In his day, scientists had evidence for quite some time that light had wave-like properties. McDougall reasoned that if the soul is a space-filling substance, it must either be made of matter that is subject to gravity or ether. He ended up concluding that it's probably made of matter and has weight. Today, standard physics doesn't accept the idea that this ether exists but in McDougall's day, it was a standard opinion.