M. BecquGrelo/^ the electrical properties of Tourmaline. 53 



during the space of one hour, especially if care be taken to 

 keep it from the action of heat. 



As soon as the tourmahne is become electrical, it is placed 

 between the two rods, the opposite poles being placed together; 

 and if it is shifted from this position, it returns by a series of 

 oscillations, of ^yhich the number in a given time will serve to 

 determine the intensity of the electricity. The following table 

 contains several results : — 



The temperature had been raised to 115° ; at 105° the tour- 

 maline, although it had been electrical before, began to fix it- 

 self between the two vertical rods which communicated with 

 the dry pile ; at 100° the oscillations were measureable. The 

 preceding results prove that from 115° to 100°, the time when 

 the cooling is the greatest, the electrical intensity increases very 

 slowly; that from 100° to 70° the increase is rapid ; that from 

 70° to 40^ it is stationary ; from 40° to 20° it diminishes nearly in 

 the same proportion at which it had increased from 100° to 70°. 

 The electrical polarity disappeared altogether at 15°, although 

 it had began at 30°. Several tourmalines have given similar 

 results. We see, then, that the electrical intensity of each pole 

 is not caused by the suddenness of the cooling. If it is easy 

 to measure the electrical intensity of the tourmaline during 

 its cooling, it is not so during the elevation of the temperature; 

 for although the polarity be then sufficiently strong, it is not, 

 however, strong enough to enable us to determine the difference 

 of intensity which arises from the increase of temperature, by 

 employing the method of oscillations. 



Hence we see that there exists a marked difference between 



