ELECTRIC PH ANOMENA OF THE ATMOSPHERE. 389 
tensions depends on the difference of the reactions upon the ex- 
tremities. 
26. To facilitate reading the electrometer I make the experi- 
ment in an inverse manner. In weather when the air is charged 
with resinous vapours, when it is necessary to raise the instru- 
ment one or two meters, it would not be convenient, and fre- 
quently even it would not be possible, to read accurately the 
number of degrees which are indicated by the gold leaves or the 
index of my electrometer. To this difficulty are to be added 
those which depend on the wind, the rain, the heat of the sun, 
and especially that which arises from the electric tension which 
the head of the observer assumes in the open air. To avoid 
these inconveniences I deposit and read off the charged elec- 
trometer in the chamber below the terrace on which I operate. 
When I wish to interrogate the electric tension collected in 
the atmosphere, I ascend to the terrace, place the instrument 
upon a stand raised 1 meter 50 certimeters, and neutralize it 
by touching the lower part of the stem; I then descend, and 
place the instrument on the stand which is intended for it; all 
this is done with great rapidity, and does not require eight 
seconds. 
27. While neutralizing the instrument the arm must be raised 
as little as possible, for if it be raised so high as to touch the 
globe, the hand, becoming resinous by induction, would repel 
the resinous electricity of the ball; it would there neutralize the 
vitreous portion which it would attract, and the instrument 
would be resinously charged at the moment of removing the 
hand. The stem must therefore be touched as low as possi- 
ble, and with a slender body, as a metallic wire, in order to 
avoid the induction of the mass of the hand on the remainder 
of the stem. Being neutralized before its elevation, the instru- 
ment on lowering gives signs of resinous electricity, whilst on 
raising it, it gives vitreous signs, which is what we have demon- 
strated above. When we thus operate it is necessary to recall 
this change of sign to mind, in order not to attribute a contrary 
electricity to the atmosphere. A vitreous tension is to be noted 
when the electrometer gives a resinous sign on descending, and 
a resinous tension of the atmosphere is indicated if the instru- 
ment brought down into the chamber gives a vitreous sign. 
28. There is one more observation which we ought not to 
omit, it is that the divergence of the leaves or the deviation of 
