310 THE PRINCIPLES OF SCIENCE. 



to be Is there any breach of the law at all ? It may 

 be that the supposed exceptional fact is not a fact at 

 all, that it is a mere figment of the imagination. When 

 King Charles requested the Royal Society to investigate 

 the curious fact that a live fish put into a bucket of 

 water does not increase the weight of the bucket and 

 its contents, the Royal Society wisely commenced their 

 deliberations by inquiring whether the fact was so or not. 

 Every statement, however false, must have some cause or 

 prior condition, and the real question for the Royal Society 

 to investigate was, how the King came to think that the 

 fact was so. Mental conditions, as we have seen (vol. ii. 

 p. 4), enter into all acts of observation, and are often a 

 worthy subject of inquiry. But there are many instances 

 in the history of physical science, in which much trouble 

 and temporary error have been caused by false assertions 

 carelessly made, and carelessly accepted without experi 

 mental verification. 



The reception of the Copernican theory was much im 

 peded by the objection, that if the earth were perpetually 

 moving, a stone dropped from the top of a high tower 

 should be left behind, and should appear to move towards 

 the west, just as a stone dropped from the mast-head of 

 a moving ship would fall behind, owing to the motion of 

 the ship. The Copernicans attempted to meet this grave 

 objection in every way but the true one, namely, that of 

 showing by trial that the asserted facts are not correct 

 ones. In the first place, if a stone had been dropped with 

 suitable precautions from the mast-head of a moving ship, 

 it would have fallen close to the foot of the mast, because 

 by the first law of motion it would remain in the same 

 state of horizontal motion communicated to it by the 

 mast. As the anti-Copernicans had assumed the contrary 

 result as certain to ensue, their argument would of course 

 have fallen through at once. Had the Copernicans next 



