14-0 0)t the Law (yf Symmetry^ 



towards the form of greatest symmetry, are constantly to be ob- 

 served. Can any thing surpass the symmetry which light dis- 

 plays in every case in which it can be rendered visible? When 

 a ray falls upon a reflecting surface, not only does it rise up at 

 the same angle, so as to produce a symmetrical reflected ray 

 when the reflecting surface is smooth, but even a considerable 

 roughness of the reflecting plane is inadequate to disperse it. 

 The forms developed by difl'raction, by polarization, by optical 

 instruments, also, are all kaleidoscopic, remarkable at once for 

 the perfection of their symmetry and the tessularity of their 

 aspect. Look to those also which are seen with polarized light 

 around the axes of untessular crystals, or transparent solids of 

 artificial origin, mechanically compressed in certain regions, or 

 unequally heated, or to those spectra which may be produced 

 by light diff'racted through small apertures, after the method of 

 Frauenhofer; and whether it be lemniscoids, ellipses, or circles 

 we see, does not every thing beheld present traces or projections 

 of spheres, or figures indicating spheres or spheroids, involved 

 in the angular form we look upon, but only to be detected by 

 this refined instrument of analysis. Suppose, for instance, that 

 we look along the axis of a rhomboid of calcareous spar, then, 

 though every line discernible in the whole crystal by ordinary 

 vision be straight, and the relationships of all the lines be 

 oblique angular, directly when viewed in polarized light, is a 

 series of concentric circles discovered to us, whose common centre 

 is traversed by two lines rectangularly disposed to each other, so 

 as to present a projection of a tessular combination If, again, 

 we take a piece of glass to which a cubical form has been given 

 by art, on inducing an unequal heat upon the exterior and inte- 

 rior, and viewing it with polarized light, we shall see four coloured 

 circles in it, symmetrically related to each other, and similarly 

 disposed in certain regions of the cube, thus indicating the exist- 

 ence of spherical or spheroidal arrangements of some sort sub- 

 sisting within the confines of the hexahaedron. In like manner, 

 if we inspect those figures which were obtained by Frauenhofer 

 in his experiments on diffraction, and which cannot but be re- 

 garded as cleavages of etherial crystallizations, do we not see the 

 most beautiful exhibition of tessularity that can be conceived .? 

 In one word, the totality of the phenomena which the medium 



