670 THE PRINCIPLES OF SCIENCE. [CHAP. 



In short, chemists can at present make nothing of these 

 anomalies. As Hofmann says, " Their philosophical inter- 

 pretation belongs to the future . . . They may turn out to 

 be typical facts, round which many others of the like kind 

 may come hereafter to be grouped ; and they may prove to 

 be allied with special properties, or dependent on particular 

 conditions as yet unsuspected." x 



It would be easy to point out a great number of other 

 unexplained anomalies. Physicists assert, as an absolutely 

 universal law, that in liquefaction heat is absorbed; 2 

 yet sulphur is at least an apparent exception. The two 

 substances, sulphur and selenium, are, in fact, very ano- 

 malous in their relations to heat. Sulphur may be said 

 to have two melting points, for, though liquid like water 

 at 120 C., it becomes quite thick and tenacious between 

 221 and 249, and melts again at a higher temperature. 

 Both sulphur and selenium may be thrown into several 

 curious states, which chemists conveniently dispose of by 

 calling them allotropic, a term freely used when they are 

 puzzled to know what has happened. The chemical and 

 physical history of iron, again, is full of anomalies ; not 

 only does it undergo inexplicable changes of hardness and 

 texture in its alloys with carbon and other elements, but 

 it is almost the only substance which conveys sound with 

 greater velocity at a higher than at a lower temperature, 

 the velocity increasing from 20 to 100 C., and then de- 

 creasing. Silver also is anomalous in regard to sound. 

 These are instances of inexplicable exceptions, the beariig 

 of which must be ascertained in the future progress of 

 science. 



When the discovery of new and peculiar phenomena 

 conflicting witn our theories of the constitution of nature 

 is reported to us, it becomes no easy taek to steer a philo- 

 sophically correct course between credulity and scepticism. 

 We are not to assume, on the one hand, that there is any 

 limit to the wonders which nature can present to us. 

 Nothing except the contradictory is really impossible, and 

 many things which we now regard as common-place were 

 considered as little short of the miraculous when first 



1 Hofmann '^'Introduction to Chemistry, p. 198. 



2 Stewart's Elementary Treatise on Heat, p. 80. 



