Space is the field in which we must operate, and contain the raw materials which we must use. The claim has been made that space is non-existent to mind or spirit, because it does not require appreciable time for the transference of thought; but the validity of this deduction has not been proved. The distances with which we are able to deal are very limited; it might require a measurable time to send thought to the sun, or to the planet Mars, or for a spirit to travel those distances. Again, the argument is advanced that the moon “acts” on the earth; and that, as a thing cannot act where it is not, there is no space between the moon and the earth; but this is puerile. The moon does not, and cannot act on the earth, because it does not touch the earth; if it affects the earth at all, it must act on something which is between them, and which in turn acts on the earth. And this something which is between the earth and the moon occupies space. I have spoken of filled space and empty space. I do not know whether empty space exists or not, but it is quite thinkable that it should exist. There may be portions of empty space, surrounded by filled space; or there may be endless extensions of empty space, side by side with endless extensions of filled space; I do not know. I know that there is filled space, and that there may be empty space. But, if there is filled space, what fills it? The answer to this must be in one word--Substance. That which is not substance is not anything, and that which is not anything cannot fill space. Space is filled by substance, and cannot be filled by anything else; but what is substance, and how do we know that it exists? That we leave for the next chapter, closing this with the claim that we have demonstrated that we live in space, and that life consists in making use of time. III. Substance. REAL NATURE OF SUBSTANCE--A CURIOUS FACT CONCERNING THE GROWTH OF VEGETABLES--DOES SUBSTANCE OCCUPY ALL OF SPACE?--THE THREE GREAT REALITIES.