PRIMARY CONCEPTS OF MODERN SCIENCE. 229 



perception of one who looks at him, nor the inference of one who 

 allows for the ship's motion, is any thing like the truth. Nor, indeed, 

 on further consideration, shall we find the revised conclusion much bet- 

 ter. For we have forgotten to allow for the earth's motion in its 

 orbit. This being some 68,000 miles per hour, it follows that, assuming 

 the time to be mid-day, he is moving, not at the rate of 1,000 miles 

 per hour to the east, but at the rate of 67,000 miles per hour to the 

 west. Nay, not even now have we discovered the true rate and the 

 true direction of his movement. With the earth's progress in its 

 orbit, we have to join that of the whole solar system toward the con- 

 stellation Hercules ; and, when we do this, we perceive that he is mov- 

 ing neither east nor west, but in a line inclined to the plane of the 

 ecliptic, and at a velocity greater or less (according to the time of the 

 year) than that above named. To which let us add that, were the 

 dynamic arrangements of our sidereal system fully known to us, we 

 should probably discover the direction and rate of his actual move- 

 ment to differ considerably even from these. How illusive are our 

 ideas of motion is thus made sufficiently manifest. That which seems 

 moving proves to be stationary ; that which seems stationary proves 

 to be moving ; while that which we conclude to be going rapidly in 

 one direction turns out to be going much more rapidly in the opposite 

 direction. And so we are taught that what we are conscious of is not 

 the real motion of any object, either in its rate or direction, but merely 

 its motion as measured from an assigned position — either the position 

 we ourselves occupy or some other. Yet in this very process of con- 

 cluding that the motions we perceive are not the real motions, we tacitly 

 assume that there are real motions. In revising our successive judg- 

 ments concerning a body's course or velocity, we take for granted that 

 there is an actual course or an actual velocity — we take for granted 

 that there are fixed points in space with respect to which all motions 

 are absolute / and we find it impossible to rid ourselves of this idea. 

 Nevertheless, absolute motion cannot even be imagined, much less 

 known. Motion, as taking place apart from those limitations of space 

 which we habitually associate with it, is totally unthinkable. For mo- 

 tion is change of place ; but, in unlimited space, change of place is 

 inconceivable, because place itself is inconceivable. Place can be con- 

 ceived only by reference to other places ; and, in the absence of objects 

 dispersed through space, a place could be conceived only in relation 

 to the limits of space ; whence it follows that in unlimited space place 

 cannot be conceived — all places must be equidistant from boundaries 

 that do not exist. Thus, while we are obliged to think that there is 

 an absolute motion, we find absolute motion incomprehensible." 



I have quoted this elaborate exposition from the text of Mr. Spen- 

 cer, because it most clearly evinces the difficulty experienced even by 

 those who habitually insist upon the relativity, not only of all our 

 actual knowledge, but also of all our possible cognition, in freeing 



