Structure of the Universe 395 



whole and also the individual movement of the particles of which 

 the mass is composed with relation to each other. The movement 

 of the mass as a whole is called the mean motion, and the relative 

 movement of the particles in the mass is the relative motion of the 

 medium. 



The Pressure and Stress of the Medium. 



Let us now ask, What is the pressure of this medium of space? 

 We certainly do not feel its pressure; neither do we feel atmospheric 

 pressure, though we know that the atmospheric pressure on the sur- 

 face of the earth at sea level is nearly 15 pounds on the square inch. 

 At great ocean depths we also know that the hydraulic pressure 

 amounts to several tons per square inch; and we also know that as 

 we go down into the earth the pressure of the surrounding rocks 

 and strata increases very rapidly, until at great depths it amounts 

 to hundreds of tons on the square inch. We probably do not realize 

 that every square foot of surface of a man's body is subjected to an 

 atmospheric pressure of about one ton, so if the surface area of a 

 human body is say 10 feet, that body is subjected to a total pressure 

 of about 10 tons. We are ordinarily unconscious of such a pressure, 

 because it presses upon us equally in all directions, but if this pressure 

 should be suddenly removed from one side of our body we would soon 

 realize it, and the pressure on the other side would hurl us through 

 space with the speed of a cannon ball. 



Located as we are on our tiny earth, which is whirling through 

 infinite space at a speed of 19 miles per second, we are immersed in 

 a vast ethereal ocean. Can we ascertain whether the medium of this 

 ocean has any pressure? Reynolds shows that the mean pressure of 

 the medium of this universal ocean of space is nearly seven hundred 

 and fifty thousand tons on' the square inch, being more than three 

 thousand times greater than the strongest material can sustain. A 

 statement like this seems paradoxical, and we cannot by any stretch 

 of the imagination conceive of such a pressure existing in what we 

 have hitherto regarded as empty space. Yet such is the sober truth, 

 found necessary to account ' for the physical facts that we know. 

 Clerk Maxwell, the great Scotch mathematician and physicist, arrived 

 at the same conclusion as to pressure and stress of the ether from a 

 consideration of electromagnetic and electrostatic forces. In his 

 article on "Attraction" in the Encyclopoedia Brittanica, after discuss- 

 ing this subject, he says: "The state of stress, therefore, which we 

 must suppose to exist in the invisible medium is 3,000 times greater 

 than that which the strongest steel could support." 



Now it seems rather strange to us at first that the medium of 

 space is of such great density. We have been accustomed all our 

 lives to think of matter as being in fact the only solid reality, and 

 universal space as simply nothing. It will thus be seen that the old 

 style philosophical materialist will find slight comfort in Reynolds' 

 theory, for the materialist's so-called real matter is shown to be only 

 a kind of froth or foam or bubble in the universal granular ocean, 

 which is ten thousand times denser than water. The presence of 

 what we call "matter" in space means a place where there is a sort 



