For the next subdivision several of the blocks of the second subdivision cemented together in certain shapes would form building-stones, and so on to the lowest.
To transfer any substance from the solid condition to the liquid (that is to say, to melt it) is to increase the vibration of its compound molecules until at last they are shaken apart into the simpler molecules of which they were built.

This process can in all cases be repeated again and again until finally any and every physical substance can be reduced to the ultimate atoms of the physical world.
Each of these worlds has its inhabitants, whose senses are normally capable of responding to the undulations of their own world only.

A man living (as we are all doing) in the physical world sees, hears, feels, by vibrations connected with the physical matter around him.

He is equally surrounded by the astral and mental and other worlds which are interpenetrating his own denser world, but of them he is normally unconscious, because his senses cannot respond to the oscillations of their matter, just as our physical eyes cannot see by the vibrations of ultra-violet light, although scientific experiments show that they exist, and there are other consciousnesses with differently-formed organs who _can_ see by them.

A being living in the astral world might be occupying the very same space as a being living in the physical world, yet each would be entirely unconscious of the other and would in no way impede the free movement of the other.