410 BULLETIN OF THE UNITED STATES FISH COMMISSION. I 
and tlie weight ia grammes of the water vapor iu the air, or the actual humidity. The j 
clouds and the state of the at mosphere were also recorded. The following table con- ' 
tains the rate of change of potential the temperature T in centigrade degrees, the fi 
relative humidity R. H., the water vapor W. in grammes, and. the estimated clouds. 
dv 
dn 
T. 
R. H. 
W. 
Cloud. 
100 
24.5 
70.8 
15. 70 
0 
7 
19.7 
84.2 
14. 15 
4 
25 
23.9 
76.8 
16. 47 
3 
28 
20.3 
83.5 
14.57 
2 
75 
25.0 
60.8 
13. 88 
5 
60 
25. 0 
56.2 
12. 83 
2 
20 
22.0 
70.2 
13.51 
1 
Clear overhead. 
45 
22.7 
71.1 
14. 23 
i 
12 
21. 6 
71.2 
13.40 
Haze overhead. 
27 
21. 8 
74.2 
14. 11 
Light stratus overhead. 
33 
22.1 
7.5.7 
14.66 
1)0. 
50 
23.4 
90.3 
18.71 
Liffht stratus ; clear overhead. 
20 
27.2 
69.0 
15. 23 
Lijiht cinus just forming. 
25 
24.4 
01.1 
20. 12 
4 
Clear overhead. 
In this table there does not appear any simple relation between the potential |H 
changes and the humidity. According to Exner the water vapor passes into the | 
atmosphere negatively charged, and as it is present in greater or less amount the I 
normal rate of rise of potential is more or less diminished. Arrhenius considers the | 
free negative charges which lower the potential to reside on small dust or water ' 
particles floating in the air, which have become charged by electrolytic conduction 
through the air of electricity from the earth. To test between these views, a large ’ 
number of observations should be made in fine cloudless weather. No conclusion in 
favor of either of them can be drawn from these observations. There seems to be a = 
relation between the rise of potential and the clearness of the sky, although there are i 
some marked exceptions to the rule that the clearer sky accompauies the greater rise i 
of potential. 
The observations here given were not reduced to the sea level by auxiliary meas- 
urements made at a distance from the vessel. The collector was held as far away as 
practicable from the sails and standing rigging. When the collector was held at a 
height of 4 metres and close to the mainsail there could not be detected any differ- 
ence of potential between the collector and the ground. This is in accord with the 
experiments of Exner on the electrical state near buildings and high cliffs. The 
equipotential surface of zero potential passes over all bodies on the earth’s surface, 
unless they are especially and carefully insulated. It is not unlikely that some of the 
inconsistencies noticed in the observations were due to the different positions of the 
mainsail at the times that they were taken. In future observations it would be 
advisable to use a water-dropper collector lashed in the main shrouds on the weather 
side of the vessel. If such a collector were fitted with a long dropping tube it would 
be practically independent of any ordinary changes in the vessel’s trim. 
