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Conduction of Galvanic Electricity through Moist Air; 207 
cally in the earth, the needle was deflected forty degrees, and the 
quantity of electricity afforded was sufficient to operate the mag+ 
nets used in Morse’s telegraph, as witnessed by the Professor, and 
others present. Is the conduction through the material of the 
building or through the earth and intervening atmosphere? Prob- 
ably through the mass of the building, which is constructed of 
blocks of sandstone, the walls being 2} ft. in thickness. A small 
Piece of this stone was found not to conduct this current percep- 
tibly, either dry or when moistened with water. But when mois- 
- .tened with acidulated water, the current passed feebly. The 
fact is interesting whether the air or sandstone becomes the con- 
ductor; for if the conduction be through the building, it is 
through a material which in a block of eight or ten cubic inches, 
is apparently a non-conductor, but which in the aggregate of the 
immense pile of the edifice is a conductor. 'The extreme sensitive- 
hess-of the galvanoscope is evident from its frequent disturbances 
from the slightest causes. Imay safely say that the needle is affect- 
ed by a flash of'lightning one hundred miles distant. Whenever a 
thunder cloud is visible, the needle is deflected at each flash of 
lightning, and the deflection is in one or the other direction, as 
the induced current varies according to the direction of the light- 
ning. When the thunder cloud is near, the action upon the 
_ Needle is very strong and has several times twisted it suddenly 
off from the silken fibre to which it is attached. When no cloud 
is visible in the horizon, the needle on certain days—particularly 
at noon when thunder storms most frequently occur—is subject 
to frequent disturbances, resembling the former. I may remark 
here, as evidence of the rapidity of induction, the movement of 
the needle and flash of lightning appear simultaneous to the eye. 
: 1e extraordinary influences upon the needle, having 
a kind of periodicity, which cannot yet be accounted for, or iden- 
tified with any meteorological fluctuations. There are also reg- 
ular changes, which have thus far been noticed during the day. 
In the morning the current is at its maximum. About 10 o’clock 
here ara a 
A) M. it declines, and gets to its minimum about half past 2 p. 
M., when the needle begins to return and arrives within four or 
five degrees of its maximum of deflection at 8 Pp. M. Whether 
his point observed at 8 a. m. is the real maximum is not known, 
_ 48 Thave not been able to observe it in the night. The range of 
Vatiation from morning to night is about ten degrees. I have not 
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