356 On the Influence of Temperature, €8c. [May, 
cury, and in general all the metals, lose their power by the action 
of cold more easily than in winter. 
It results from this fact that a certain degree of cold weakens and 
destroys the electric power of all bodies, and that this degree is not 
the same for all. 
Third Fact.—1. On a day when the electric tension is strong, 
and when the rod is decidedly negative in mercury at the common 
temperature of the air, if we gradually cool down another vessel of 
mercury to 32°, and plunge a glass rod into it at each degree which 
its temperature sinks, it becomes at first more and more negative 
the lower the temperature sinks. If we continue the immersions, 
it comes out less and less negative, and at last inexcitable without 
the electricity changing its nature. If we then allow the mercury 
and the rod to recover the temperature of the air, the rod becomes 
again electric, and the electricity is always negative. 
The case is different when we preserve the mercury at the tem- 
perature of the air, and gradually cool the rod to 32°. It becomes 
at first less and less negative, then inexcitable, then positive, and 
at last inexcitable. When we allow it to come to the temperature 
of the air, it becomes successively positive, inexcitable, and nega- 
tive, even more negative than at first. 
The electricity of the rod, then, remains negative when we 
weaken the power of the mercury; and it becomes positive when 
we weaken the power of the glass. 
2. When the rod is strongly negative with a north wind, and at 
a time when the thermometer in the open air is 171°, if we expose 
to the open air a glass rod of the size of roll sulphur, and if we 
take care to carry it into the room every minute, plunging it each 
time into mercury of the temperature of the room, it comes out at 
first less negative, then inexcitable. Some time after it appears 
positive, and again inexcitable. By and by it appears weakly posi- 
tive, and then finally inexcitable. It is in vain after this to leave it 
exposed to the cold; no electricity appears when it is plunged into 
the mercury. When we allow it to recover the temperature of the 
room, plunging it at intervals into the mercury, we see it becoming 
successively positive, inexcitable, negative, inexcitable, positive, 
inexcitable, and at last negative, as before the experiment. 
We can at all seasons obtain the same result by cooling the rod 
by repeated doses of ether. 
When the rod is going to change its state, the new electricity 
begins always at one of the extremities, while the old still subsists 
at the other. These two electricities are separated from each other 
by an inelectrical space. It is in such a case that the rod comes out 
of the mercury sometimes positive at the top and negative at the 
bottom, sometimes negative at the top and positive at the bottom. 
3. When the rod is naturally inexcitable in the mercury, if the 
mercury and the glass are both without power when rubbed with 
flannel, and if we cool the rod with ether, it becomes weakly nega- 
tive in the mercury. If the mercury is still capable of becoming 
