xxix.] EXCEPTIONAL PHENOMENA. 647 



expand by heat," if I know that water below 4 C. does 

 not ; I ought to say, " All liquids, except water below 4 C., 

 expand by heat ; " and every new exception discovered will 

 falsify the statement until inserted in it. To speak of 

 some laws as being generally true, meaning not universally 

 but in the majority of cases, is a hurtful abuse of the word, 

 but is quite usual. General should mean that which is 

 true of a whole genus or class, and every true statement 

 must be true of some assigned or assignable class. 



Imaginary or False Exceptions. 



When a supposed exception to a law of nature is brought 

 to our notice, the first inquiry ought properly 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, but 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 Eoyal 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, enter into all acts of observation, and are 

 often a worthy subject of inquiry. But there are many 

 instances in the history of science, in which trouble and 

 error have been caused by false assertions carelessly made, 

 and carelessly accepted without verification. 



The reception of the Copernican theory was much 

 impeded by the objection, that if the earth were 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 

 Copermcans attempted to meet this grave objection in eveiy 

 way but the true one, namely, showing by trial that the 

 asserted facts are not correct. 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 



