102 ANNUAL OF SCIENTIFIC DISCOVERY. 



tube is filled with a peculiar glow or light, aboundiug iu Stokes' 

 rays. 



"The experiments with the vacuum tube, and especially Gas- 

 siot's cascade, are, as might be expected, very beautiful. Wlieu 

 a coal-gas vacuum tube of considerable diameter, and conveying 

 the full discharge from the secondary coil, is supported over a 

 powerful electro-magnet axially, the discharge is condensed and 

 heat is produced. 



"If placed equatorially, the heat increases greatly, and when 

 the discharge is condensed and impinges upon the sides of the 

 glass tube, it becomes too hot to touch, and if the experiment 

 was continued too long the tul)e would crack. 



"The enormous quantity of electricity of high tension which 

 the coil evolves, when connected with a battery of 40 cells, is 

 shown by the rapidity with which it will charge a Leyden bat- 

 tery. 



"Under favorable circumstances, 3 contacts with the mercurial 

 break will charge 40 square feet of glass. 



" On one occasion a series of 12 large Leyden jars arranged in 

 cascade were discharged ; the noise was great ; and each time 

 the spark (which was very condensed and brilliant) struck the 

 metallic disc, the latter emitted a ringing sound, as if it had re- 

 ceived a sharp blow from a small hammer. 



" The discharges were made from a point to a metallic disc ; 

 and when the former was positive the dense spark measured from 

 18i to 18| inches, and fell to two and one-half inches when the 

 metallic plate was positive and the point negative. 



" Variations of the Leyden-jar experiments were tried by con- 

 necting the coil worked by a quantity battery of 2o -\- 25 cells 

 with G Leyden jars arranged in cascade, and the spark obtained 

 measured 8i inches. 



" The same 6 jars connected with the coil, when the 50 cells 

 were arranged continuously for intensity, gave a spark of 12 

 inches, of very great density and brilliancy." 



ELECTRICITY APPLIED TO REGISTERING VIBRATIONS. 



The laws which govern the vibration of cords or wires have 

 been obtained by comparing thb sounds they produce with the 

 notes of a syren. Without questioning the accuracy of this 

 method, it will still be desirable to obtain the laws of vibration 

 without regard to the eftects which vibrations produce ; a direct 

 registry cannot fail to be more satisfactory. Now it is clear that 

 however rapid may be the vibrations of a cord, the velocity of the 

 electric force is greater; moreover, it is not impossible to make a 

 succession of electric impulses produce a corresponding succes- 

 sion of pennanent effects, which can be seen and counted, so that 

 if a vil)rating body can be made to open and close an electric cur- 

 rent, the electric force may be depend<Ml on to register its vibra- 

 tions. The practical questions are, first, tlow shall a vibrating 

 body be made to open and close an electric current without hav- 



