88 FRAGMENTS OF SCIENCE 



Guided by analogy, you may, if you like, suppose 

 that, swarming among the constituent molecules of the 

 salt, there is an invisible population, controlled and co- 

 erced by some invisible master, placing the atomic blocks 

 in their positions. This, however, is not the scientific 

 idea, nor do I think .jour good sense will accept it as 

 a likely one. The scientific idea is that the molecules 

 act upon each other without the intervention of slave 

 labor; that they attract each other, and repel each other, 

 at certain definite points, or poles, and in certain definite 

 directions; and that the pyramidal form is the result of 

 this play of attraction and repulsion. While, then, the 

 blocks of Egypt were laid down by a power external to 

 themselves, these molecular blocks of salt are self -posited, 

 being fixed in their places by the inherent forces with 

 which they act upon each other. 



I take common salt as an illustration, because it is so 

 familiar to us all; but any other crystalline substance 

 would answer my purpose equally well. Everywhere, in 

 fact, throughout inorganic nature, we have this formative 

 power, as Fichte would call it this structural energy 

 ready to come into play, and build the ultimate par- 

 ticles of matter into definite shapes. The ice of our 

 winters, and of our polar regions, is its handiwork, and 

 so also are the quartz, felspar, and mica of our rocks. 

 Our chalk-beds are for the most part composed of minute 

 shells, which are also the product of structural energy; 

 but behind the shell, as a whole, lies a more remote and 

 subtle formative act. These shells are built up of little 

 crystals of calc-spar, and, to form these crystals, the 

 structural force had to deal with the intangible mole- 

 cules of carbonate of lime. This tendency on the part 



