214 ELECTRIC POWER. 



bodies, and does not require an elevation of temperature to 



% urge that of the mercury. 



Effects of the \\\ m Glass, sulphur, amber, and sealing wax, are constantly 

 third process, , • , , . . , . . ,. / 



called emer- electrical, even by immersion, when their temperature isa little 



sion frominer- higher than that of the mercury ; a single degree of difference 

 firsf class"of * between the temperature of the rubbing body, and that which 

 bodies. is rubbed, is then sufficient to determine an electric state, and 



this power is more intense, the greater the interval between the 

 Singular effect two temperatures. Nevertheless, there are limits beyond which 

 plunged hf* li disappears ; for example, when a cylinder of glass at 100°. c. 

 cold mercury, is plunged in mercury at 18©. c. the glass then comes forth 

 without electricity, provided the sudden contraction produced 

 by the cold do not crack it, but if it do, the glass becomes 

 extremely electric. 

 If it crack, it This want of excitability in very hot glass, plunged in very 

 trifled 1 e but 6C " c °k* raercur y> when it does not crack, appears to me to be an 

 otherwise not. effect of the contraction of the glass which prevents the caloric 

 from radiating outward, and forces it to radiate or return into 

 the interior of its substance. It is, no doubt, from this reason, 

 that workmen in glass houses can touch with impfunity, a mass 

 of red hot iron in fusion when plunged in water. 

 Explanation I have asserted, that a single degree of difference of tem- 

 theimometri- perature between the mercury and the rubbed body, is sufficient 

 cal difference, to determine the electric state j but this is not to be understood 

 but with regard to temperatures remote from the two extremes 

 at which the electric power is extinguished. Thus sealing 

 wax at 8°. c. is weakly electrified in mercury at 0°. c. and 

 strongly at 8°. c. and so likewise at 4°. c. it is no longer elec- 

 trified in mercury at 0°. c. but it continues to be so by the 

 stroke in mercury at 18°. c. The same thing is observed in all 

 the other bodies at some differences in their degrees in relation 

 to their specific heat. Silk, for example, at . c. is still electric 

 in mercury at 15°. c. ; it is even so when itself at 4°. c. in 

 mercury at 15°> c. but at 5°. c. it no longer shews any elec- 

 tricity. 

 Experiments IV. After having determined the influence of heat upon the 

 mercury was electric P ower when lt radiates from the body rubbed into 

 colder than mercury, I was desirous of seeing whether the same effect would 



body mm The d take P lace when the heat should P ass from the mercury into 

 effects were the immersed body. A tube of glass, particularly when the 

 much less. temperature 



