108 



much better. For we liave forgotten to allow for the earth's 

 motion in its orbit. This being some 68;000 miles per hour^ it 

 follows that^ assuming that time to be midday, 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 towards the constellation 

 Hercules; and when we do this, we perceive that he is moving 

 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 movement 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 j 

 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 concluding that the 

 motions we perceive are not the real motions, we tacitly assume 

 that there are real motions.''^ 



21. I affirm that all the motions mentioned here are real 

 motions, and not mere illusions, or apparent motions. They are, 

 doubtless, motions in diflFerent directions, but not the less real on 

 that account. It might be difficult to determine at any given 

 moment the absolute positions of the ship, captain, and earth, 

 in reference to some particular far-off world ; but that diffi- 

 culty is the result of their each moving at the same time. 

 The captain, while walking the deck, may keep the same 

 position relatively to an object on shore ; but had he not been 

 moving on the ship at the same time the ship was moving, 

 on a moving earth, that relative position would have been at 

 once altered. Mr. Spencer in his illustration makes very clear 

 how difficult it would be to ascertain the rate at which any one 

 of the objects moved, or the actual direction ; but the fact of 

 a real motion in some direction and at some rate is beyond all 

 controversy. It is, no doubt, impossible to understand why a 



" First Principles^," p. 54. 



