Atmospheric-Electric Observations, 1909-10 



367 



The conductivity observations were taken with the Gerdieu conductivity apparatus 

 described in P. H. Dike's report on the third cruise of the Galilee,^ and the apparatus, when 

 in use, was placed on a gimbal stand amidships, between the after observatory and the 

 mainmast.^ 



Observations of temperatiu'e and humidity by means of a psycbirometer, and of the air 

 pressure, wind, clouds, and state of the sea, were made during the experiments. Obser- 

 vations for natural leakage were made at intervals; this seemed usually to decrease to a very 

 low value during the observations, and no correction for leakage was applied. 



The mean values of the conductivities \+ and X_ for positive and negative ions, and of 



the ratio— ^ are as follows:^ 



A— 



\+ =1.85X10"* e.s.u. (from 26 observations) 

 X_ =1.58X10-* e.s.u. (from 26 observations) 



^=1.16 



From the observations obtained, no connection could be established between atmos- 

 pheric pressure, humidity, wind, or cloud, and the conductivity. When, however, there 

 was a visible fog or haze the conductivity was greatly reduced. This was noticed in some 

 preliminary practice experiments at Falmouth and in Long Island Sound. Rain squalls 

 of short duration did not produce any effect. As the conductivity is an extremely variable 

 quantity, a very large number of observations is required before the connection with 

 meteorological conditions can be thoroughly investigated. One effect noticed was that a 

 low conductivity was invariably obtained when the vessel was in the neighborhood of land. 

 This effect was heightened in Long Island Sound by the state of the atmosphere, and 

 probably by the presence of snow on the land and ice on some stretches of water. 



Another noticeable fact is the persistent excess of the positive conductivity over the 

 negative. The only occasions on which the reverse appeared to be consistently the case 

 were while the ship was at anchor off Madeira and in Hamilton Harbor, Bermuda. 



so 



cd 



Ui 



25 



10 Noon 14 



16 18 20 22 Mid-n't 2 



HOURS 



Fig. 16. — Conductivity of the Atmosphere, December 18-19, 1909. 



8 



On December 18-19, 1909, continuous observations of the conductivity were taken 

 over practically 24 hours, in order to discover, if possible, a diurnal variation. The day 

 was exceedingly calm and fine, with a glassy sea with a smooth, low swell. The results 

 obtained are shown in Figure 16, the ordinates representing conductivities in e.s.u. XlO~*. 

 The continuous line corresponds to X_, the broken line to X+, and each point corresponds 

 to the mean of from 4 to 8 observations. It will be seen that the observations indicate 

 values of the conductivities which are higher by night than by day. 



'See page 365. 



'See description of the Carnegie, pages 160-163 and Plate 9, Fig. 2, Position E. 



•The original report contains the complete tables of the individual values. 



