Miscellaneous Intelligence. 431 



are positive crystals ; antimony, according to my experiments, is a 

 negative one : all are uniaxaL 



II. Cyanite is by far the most interesting crystal I have examined. 

 If suspended horizontally, it points very well to the north, by the mag- 

 netic power of the earth only. It is a true compass-needle, and more 

 than that, you may obtain its declination. If, for instance, you suspend 

 it in such a way that the line A bisecting the two optic axes of the 

 crystal be in the vertical plane passing through the axis B of the prism, 

 the crystal will point exactly as a compass-needle does. By turning the 

 crystal round the line B you may make it point exactly to the north of 

 the earth, &c. The crystal does not point according fo the magnetism 

 of its substance, but only in obedience to the magnetic action upon its 

 optical axes. This is in full accordance with the different law of 

 diminution by distance of the pure magnetic and opto-magnetic action. 

 If you approach to the north end of the suspended crystal the south 

 pole of a permanent magnetic bar, strong enough to overpower the 

 magnetism of the earth, the axis B of the prism will make with the 

 axis of the bar (this bar having any direction whatever in the horizon- 

 tal plane) an angle exactly the same it made before with the meridian 

 plane, the crystal being directed either more towards the east or more 



towards the west. 



The crystal showed, resembling in that also a magnetic needle, strong 

 polarity ; the same end being always directed to the north. I think 



>/ 



Two questions too 



may easily be answered . — 1st. Is the north pole indicated by the forms 

 of crystallization? 2nd. Did the crystal obtain, when formed, its po- 

 larity by the magnetism of the earth ? Between the poles of the strong 

 electro-magnet the permanent polarity disappeared as long as the mag- 

 netism was excited. m 



I am obliged, by the new facts mentioned above, to take up my 

 former memoir ; I must reproduce it under quite a new shape. I will 

 examine again the rock-crystal, which, being acted upon weakly by a 

 magnet, induced me to deny in that memoir, what I ascertain now and 

 what I thought most probable, as soon as I received the first notice of 

 your recent researches, [That you will find in the memoir given to 

 M. Poggendorff two or three months ago.] Perhaps the exceptional 

 molecukir condition of rock-crystal, as indicated by the passage of 

 light through it, will produce a peculiar magnetic action. 



I shoulcTbe very much obliged to you, if you would give notice of 

 the contents of mv present letter to M. De la Rive, when he calls on 

 you, as he intended to do. I showed him several of my experiments 

 when he passed through Bonn the 12th of May. The following day I 

 obtained the different results mentioned above. 



Bonn, 20th of May, 1849. 



2. Some facts relative to the Spheroidal State of Bodies, Fire- Ordeal, 

 Incombustible Man, SfC. ; by P. H. Boutigny (d'Evreux), (Comptes 

 Rendus, May, 1849 ; Phil. Mag., [3], xxxv, 60.)— In the year 241, Sapor 

 or Chapour ordered the Magi to do all in their power to persuade them 

 and bring them back to the faith of their ancestors. It was then that 

 one of the pontiffs of the dominant religion, Adurabad-Mabrasphand, 

 offered to submit to the fiery ordeal. ... u He proposed that eighteen 



