OF NATURAL PHILOSOPHY. 171 



pursuing the subject further, the same ingenious 

 enquirer happily succeeded in producing a new phos- 

 phate of soda, differing from that generally known 

 in containing a different proportion of water, and 

 agreeing in composition exactly with the arseniate. 

 The crystals of this new salt, when examined, 

 were found by him to be precisely identical in form 

 with those of the arseniate : thus verifying, in a 

 most striking and totally unexpected manner, the 

 law in question, or, as it is called, the law of 

 isomorphism. 



(181.) Unexpected and peculiarly striking con- 

 firmations of inductive laws frequently occur in the 

 form of residual phenomena, in the course of inves- 

 tigations of a widely different nature from those 

 which gave rise to the inductions themselves. A 

 very elegant example may be cited in the unex- 

 pected confirmation of the law of the developement 

 of heat in elastic fluids by compression, which is 

 afforded by the phenomena of sound. The enquiry 

 into the cause of sound had led to conclusions re- 

 specting its mode of propagation, from which its 

 velocity in the air could be precisely calculated. 

 The calculations were performed ; but, when com- 

 pared with fact, though the agreement was quite 

 sufficient to show the general correctness of the 

 cause and mode of propagation assigned, yet 

 the whole velocity could not be shown to arise 

 from this theory. There was still a residual velo- 

 city to be accounted for, which placed dynamical 

 philosophers for a long time in a great dilemma. 

 At length La Place struck on the happy idea, that 

 this might arise from the heat developed in the act 



