228 THE POPULAR SCIENCE MONTHLY. 



the reasons for assigning to it this eminent, and, as it were, sovereign 

 position, these are questions to which there is no answer. 



" It will be necessary, therefore, to establish the proposition, as the 

 first principle of the Galileo-Newtonian theory, that in some unknown 

 place of the universe there is an unknown body — a body absolutely 

 rigid and unchangeable for all time in its figure and dimensions. I 

 may be permitted to call this body " The body Alpha." It would 

 then be necessary to add that the motion of a body would import, not 

 its change of place in reference to the earth or sun, but its change of 

 position in reference to the body Alpha. 



" From this point of view the law of Galileo is seen to have a definite 

 meaning. This meaning presents itself as a second principle, which is, 

 that a material point left to itself progresses in a straight line — pro- 

 ceeds, therefore, in a course which is rectilinear in reference to the 

 body Alpha." 



It will be observed that the assumption which underlies all this 

 reasoning of Prof. Neumann is that, to conceive motion as real, it is 

 necessary to conceive it as absolute — an assumption in every respect 

 analogous to that of Prof. Tyndall, according to which the reality of 

 matter implies its constitution from absolute, unvarying elements. 

 The logical parentage of the body Alpha is precisely the same as that 

 of the " atom." And I may add that the assumption of Prof. Neu- 

 mann is the tacit assumption of almost all the physicists and philoso- 

 phers of the day, although it is not usually developed to its last con- 

 sequences. It is one of the tasks of Herbert Spencer, for instance, to 

 exhibit the contradictions involved in the essential relativity of motion. 

 " A body impelled by the hand," says Spencer (" First Principles," 

 chap, iii., § 17), "is clearly perceived to move, and to move in a def- 

 inite direction : there seems at first sight no possibility of, doubting 

 that its motion is real, or that it is toward a given point. Yet it is 

 easy to show that we not only may be, but usually are, quite wrong in 

 both these judgments. Here, for instance, is a ship which, for sim- 

 plicity's sake, we will suppose to be anchored at the equator, with her 

 head to the west. When the captain walks from stem to stern, in 

 what direction does he move ? East is the obvious answer — an an- 

 swer which for the moment may pass without criticism. But now the 

 anchor is heaved, and the vessel sails to the west with a velocity equal 

 to that at which the captain walks. In what direction does he now 

 move when he goes from stem to stern ? You cannot say east, for the 

 vessel is carrying him as fast toward the west as he walks to the east ; 

 and you cannot say west, for the converse reason. In respect to sur- 

 rounding space, he is stationary, though to all on board the ship he 

 seems moving. But now are we quite sure of this conclusion? Is he 

 really stationary ? When we take into account the earth's motion 

 round its axis, we find that, instead of being stationary, he is travel- 

 ing at the rate of 1,000 miles per hour to the east ; so that neither the 



