EXCEPTIONAL PHENOMENA. 341 



complicated and disguised manner. It would be easy to 

 point out an almost infinite number of other unex- 

 plained anomalies. Physicists assert, as an absolutely 

 universal law, that in liquefaction heat is absorbed 1 , yet 

 sulphur is at least an apparent exception. 



The two substances, Sulphur and Selenium, are re- 

 markable for their relations to heat. Sulphur may 

 almost 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, melting once 

 again at higher temperatures. As well as the other 

 element named, it may be thrown into several curious 

 states, which chemists conveniently dispose of by calling 

 them attotropic, 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 aUoys with carbon and other substances, 

 but it is almost the only substance which conveys sound 

 with greater velocity at a higher than at a lower tem- 

 perature, the velocity increasing from 20 to 100 C., and 

 then decreasing. Silver is also anomalous in regard to 

 sound. These are ah 1 instances of inexplicable exceptions, 

 the bearing of which must be ascertained in the future 

 progress of science. 



When the discovery of new and peculiar phenomena 

 conflicting with our theories of the constitution of nature 

 is reported to us, it becomes no easy task 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 



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



