C. GENERAL PHYSICS. 133 



the reflecting surface in front of it is now gradually drawn 

 away from its sounding body, and at each successive point 

 of remove the pulses propagated through che two resonator 

 tubes are brought to opposition of phase on reaching the 

 membrane by means of the glass telescoping tube. Equality 

 of impulses having been obtained, we measure the distance 

 of the resonator which has not the reflecting substance in 

 front of it from the origin of its sounding body, and this 

 measure, together with the known previous distance of this 

 resonator, when equality was attained before the interposi- 

 tion of the reflecting surface, gives the data for the computa- 

 tion of the intensity of the transmitted vibration. This num- 

 ber subtracted from the measure of the intensity when Iflie 

 substance was not before the resonator, taken as unity, gives 

 the reflecting power of the substance plus its absorbing 

 power. 



REMARKABLE ELECTRICAL PROPERTY OF GLYCERINE. 



- Professor Waltenhofen finds that when a card is, coated 

 with glycerine on one side, and points connected with con- 

 ductors leading to the coatings of a Ley den jar, or the ter- 

 minals of a Ruhmkorfl" coil, are placed in contact with oppo- 

 site sides, but not exactly opposite each other, the positive 

 in contact with the coated side, the perforation by the dis- 

 charge will invariably be opposite the positive point, instead 

 of the negative, as in Lullin's experiment. 14 C, CCVIL, 

 1873,305.^ 



THE ELECTRIC PHEXOMEXA OF CRYSTALS. 



The electrical phenomena developed in many crystals by 

 heating or cooling them has not been thoroughly pursued 

 since tlie earlv davs of David Brewster until the recent in- 

 vestigations of Hankel, of Leipsic. The elaborate researches 

 of this eminent physicist have opened up new views of the 

 subject, and will undoubtedly contribute to place upon a 

 more correct basis our knowledge of the relations between 

 heat, electricity, and crystalline structure. Hankel has stated 

 some of his conclusions very nearly as follows: "Up to the 

 time of my researclies on the thermo-electric peculiarities of 

 topaz, we knew only of the electric phenomena of crystals 

 having electrically polar axes that is, of those of which one 



