and its Effects. 201 



points amounted only to 1^ millim., and both were touched by 

 the thermometer. The elevations of temperature within one 

 minute were then with — 



Platinum . . . . 23° C. 



f^^PP'^'l .... 24° to 26° C. 

 Iron J 



Silver 27° C. 



Tin 51° C. 



When placed near the stream of sparks, though scai'cely in 

 contact with it, the thermometer rose 28° C. with tin points. 



3. The inequality in the temperature of the two poles of the 

 induction wire may also be clearly shown by the thermometer. 

 When the points were 4-5 millims. apart, the elevation of tem- 

 perature during one minute was always 6 or 7 degrees more at 

 the negative than at the positive pole, both pole wires being of 

 zinc or tin, and about 1 millim. thick. 



4. When the pole wires consist of two diiFerent metals, the 

 I'ise of the thermometer placed in the stream of sparks is greatest 

 when the easily fused and vaporized metal constitutes the nega- 

 tive pole. Within one minute, and when the points were 4*5 

 millims, asunder, the elevations of temperature were, — 



. . 181 C. 



. . 231 ... 



. . 31' ... 



. . 181 ... 



. . 30 ... 



5. The greater temperature of the sparks with easily fused 

 and vaporized metals appears to be caused by the volatilization 

 of particles of the same. This is clearly shown by the thermo- 

 meter suspended in the stream of sparks; when zinc, tin, bis- 

 muth, and lead are used, the positive side is coloured white, and 

 the negative brown (at least with bismuth and lead). 



6. This volatilization appears also, by improving the conduc- 

 tibility between the poles, to produce a greater transfer of sparks, 

 and consequently a greater intensity of current. It is true the 

 galvanometric deviations caused by the induction wire during 

 the time that sparks are produced are very irregular, so much so 

 that it is exceedingly difficult to determine their magnitude, 

 nevertheless I am inclined to think that the deviations are greater 

 with tin than with platinum points. 



7. This suggested a nu;thod of proving whether the facility with 

 which sparks pass from one pole to the other is modified by the 



Phil. May. S. 4. Vol. 10. No. G5. Sept. 1855. P 



