Crystalline Structure by Compression and Traction. 263 



is quite possible, too, that these forces may have exercised some 

 influence in modifying the doubly refracting structure of the 

 substance under examination ; but as such a question has no 

 bearing upon our present subject, I have not attempted its so- 

 lution. 



Without expecting any very interesting result, I submitted to 

 examination several of the soft solids which possess double 

 refraction, such as bees 3 wax, oil of mace, tallow, and almond soap. 

 The last of these substances, though iu common use, is a very 

 remarkable one. Owing to its particles not being in optical 

 contact, it has a fine pearly lustre, and may be drawn out 

 into long and slender strings. Upon laying a portion of it on 

 glass, it has a quaquaversus polarizing structure, with a tendency 

 to form circular crystals ; but when it is drawn out into strings, 

 and laid upon glass, these strings have neutral and depolarizing 

 axes, like the streaks formed by compression and traction. In 

 the present case it is by traction alone that this crystalline 

 arrangement of the particles is produced. 



In oil of mace and tallow a similar effect is produced by com- 

 pression and traction. With bees' wax the depolarizing lines 

 are still better displayed, and the effect is considerably increased 

 by mixing the bees' wax with a small quantity of rosin. 



As the preceding experiments place it beyond a doubt that the 

 optical or crystallographic axes of a number of minute particles 

 are dragged by pressure and traction into the same direction, so 

 as to act upon light like regular crystals, it became interesting 

 to discover the cause of phsenomena which certainly could not 

 have been anticipated from any theoretical principle with which 

 we are acquainted. The primary force, and indeed the only 

 apparent one exerted in these experiments, is a mechanical force ; 

 but it is not improbable that a secondary force, namely, that of 

 electricity, may be generated by the friction which accompanies 

 the forces of pressure and traction. That such a force is excited 

 with certain crystals will not admit of a doubt ; but even if it 

 were developed in every case, this would not prove that elec- 

 tricity was the agent in producing the phsenomena under con- 

 sideration. In subjecting asparagine to compression and trac- 

 tion, I observed, upon placing it in the polarizing microscope, 

 that its particles were moving about under an electrical influence, 

 but in no other case did the same phenomenon present itself 

 to me. 



The experiments with soft solids, but especially those made 

 with the almond soap, exclude the supposition that the electricity 

 of friction is the cause of the crystalline arrangement of its par- 

 ticles ; though it is not improbable that the sliding of the par- 

 ticles upon one another, as produced by traction, and their 

 mutual separation, as in the case of tearing asunder mica or 



