Pblts per metre, Potential Gradient. Barometric Bressure. 
330 DR. C. CHREE: ATMOSPHERIC ELECTRIC POTENTIAL RESULTS AT KEW 
diurnal inequalities for the year, he found that “ the barometric curve for Halle 
bears a strong resemblance to the Kew electrical curve, but is upwards of an hour 
later in phase.” Several other writers have since called attention to general 
resemblances of this kind. Of late years, additional interest has attached to the 
possibility of the connection, owing to Elster and Geitel’s discovery that air 
drawn from the soil is ionized, and their consequent suggestion that change of 
barometric pressure may influence potential gradient, by modifying the rate at which 
this ionized air escapes into the atmosphere. 
The diurnal inequality of barometric pressure is an element considerably dependent 
on local conditions, and it thus appeared essential to an adequate discussion to have 
barometric data for Kew. Diurnal inequalities were accordingly got out by the 
Fig. 4. 
Observatory staff for each month of the year for an 11-year period 1890 to 1900, 
making use of the data published by the Meteorological Office in the ‘Hourly Means.’ 
The regular diurnal change is a small quantity, and accordingly means were 
calculated to O'OOOl inch This is perfectly legitimate, as the curves are read to 
O’OOl inch, and each hourly value in the mean diurnal inequality for a month was 
based on over 300 individual readings. For our present purpose full details of the 
diurnal inequalities are not absolutely necessary, and I have consequently omitted 
them to economise space. 
§ 27. That Everett had a substantial basis in claiming a resemblance between the 
mean diurnal inequalities for the year in barometric pressure and potential gradient 
is apparent on comparing the two curves of fig. 4. The heavy curve, representing 
Volts per metre, Potential Gradient. 'Barometric Pressure. 
