68 THE ANTARCTIC MANUAL. 
held by the observer in his left hand while he is making an observa- 
tion; but a fixed stand, when conveniently to be had, is to be pre- 
ferred, unless in the case of making observations from an open boat. 
(2) To make an observation in ordinary circumstances the observer 
stands upright and holds or places the electrometer in a position 
about five feet above the ground (or place on which he stands), so as 
to bring the hair and two black dots about level with his eye. The 
umbrella of the principal electrode being down to begin with (and so 
keeping metallic connection between the principal electrode and the 
metallic case of the instrument), the observer commences by taking 
an “earth reading.” * The steel wire, with a match stuck on its 
point, being in position on the principal electrode, the match is then 
lighted, the umbrella lifted, and the micrometer screw turned so as 
to kesp the hair in the middle between the black dots. After the 
umbrella has been up and the match lighted for 20 seconds or half 
a minute, a reading may be taken and recorded, called an “air 
reading.” A single such reading constitutes a valuable observation. 
But a series of readings taken at intervals of a quarter of a minute, 
or half a minute, or at moments of maximum or minimum electrifi- 
cation during the course of two or three minutes, the match burning 
all the time, is preferable. In conclusion, remove the match if it is 
not all burned away, lower the umbrella home, and take an earth 
reading. 
(3) The electric potential of the air at the point of the burning 
match is found by subtracting the earth reading from the air reading 
at any instant. When the air reading is less than the earth reading 
the air potential is negative, and is to be recorded as the difference 
between the earth reading and the air reading, with the sign — pre- 
fixed. The earth reading may be generally taken as the mean 
between the initial and final earth readings. But the actual earth 
readings and air readings ought all to be recorded carefully, and the 
full record kept. 
(4) Note and record the wind at the time of each observation, also 
the character of the weather. 
IV. Observations to be made: 
(1) At the commencement of the Expedition, in the course of the 
Southward voyage, observations of atmospheric electricity ought to be 
taken regularly three or four times a day; also occasionally during 
the night, to give the observer some practice in the use of a lantern 
for reading the divisions on the circle and of the vertical scale. 
(2) When stationary in winter quarters, observations should be 
* + Electrostatios and Magnetism,’ § 375. 
