340 



C. Barus — Resistance of Stressed Glass. 



stress* on electrolyzing glass, kept as nearly as practicable at 

 different constant temperatures between 100° and 360°. 



2. The apparatus with which most of my definite experi- 

 ments were madef are shown in figures 1 and 2, and are differ- 

 ential in kind. The resistances across equal parts of the walls 

 of two nearly identical glass tubes, respectively stressed and 



Figure 1.- 



for 200' 



iratus 



Figure 2. — Apparatus 

 for 100°. 



unstressed, are compared. These tubes are shown at dbcF and 

 ETihf. The ends proper are bent hook-shaped ; and those of 

 the glass tube to be oj3erated on, fastened by aid of screws and 

 cement, between slabs of wood A and B. A is fixed ; B pro- 

 vided with a hook, P, from which a scale pan may be hung ; 



* Reference may here be made to J. and P. Curie (C. R., xci, pp. 294, 383 ; xcii, 

 p. 350, 1881 ; xciii, p. 1137, 1881), and to Hankel (Wied. Ann., p. 640, 1881), 

 who show that in certain hemihedral crystals longitudinal compression is accom- 

 panied by the manifestation of electromotive force. Curie's very recent work is 

 summarized in the Beiblatter, xii, p. 857 to 867, 1888. 



f The earlier experiments were made with single tubes alternately stressed and 

 unstressed, inserted in a simple galvanic circuit. In such a case, however, fluc- 

 tuations of temperature often obscured the effect to be observed, beyond recogni- 

 tion. Cf. 8 7. 



