360 On the Influence of Temperature, @c. [May, 
rod pass to another electric state; nor is it possible to increase it 
further. _ But if we cannot augment its force by heat, we can in- 
crease it relatively by weakening that of glass by cooling it. We 
then see the rod becoming successively negative, inexcitable, and 
positive. 
Thus by increasing the power of the glass the rod becomes suc- 
cessively negative, positive, and negative, according to its degree of 
relative force; and by increasing that of the mercury, or, which 
comes to the same thing, by diminishing that of the glass, it be- 
comes successively positive, negative, and positive, according to-its 
degree of relative weakness. 
3. The rod passes successively through all these states in the 
course of the year, when its power begins to appear. It is in winter 
that it appears nascent, successively positive, negative, and positive, 
according to its degree of relative feebleness ; and it is in summer 
that it is successively negative, positive, and negative, according to 
its degree of relative force. 
When the nascent electricity of the rod in mercury commences 
by being positive, it becomes inexcitable and negative by heating it 
a few degrees. When it commences by the negative state, it be- 
comes successively positive, inexcitable, and negative, in proportion 
as we heat it. When it appears by the second state positive, we 
make it become by heating it successively negative, inexcitable, 
positive, inexcitable, and negative. 
Whatever is the state of the nascent electricity of the rod in 
winter, it comes out of mercury of the temperature 140°, or higher, 
almost always inexcitable after the first immersion. ‘Then, in pro- 
portion as it acquires heat, it becomes electric, and changes its 
electricity once or oftener, according to the state from which it 
set out. 
If we gradually heat the rod in summer, when its nascent elec- 
tricity in mercury appears in the first state negative, it becomes 
successively positive, inexcitable, and negative. When it com- 
mences by the positive state, it becomes negative on heating it, and 
does not go further. When it commences by the second state 
negative, it may become inexcitable by heating it; but it stops 
there. 
When the nascent electrical state of the rod is negative in 
summer, it always comes positive out of mercury heated to 140°, 
and it becomes negative on heating it. If it is naturally positive, it 
comes out negative, and it remains in that state, on heating it, till 
the end of its cooling, when it appears very weakly positive before 
becoming inexcitable. 
Thus in developing the powers the electricity of the rod changes 
its nature once, twice, or thrice, according to the respective state of 
the forces at the moment of development ; and in all cases it termi- 
nates by being negative when the two powers are equally developed. 
4, ‘The two powers may be inexcitable the one by the other, 
though each may be rendered weakly electrical by friction with 
