314 DR. C, CHREE: ATMOSPHERIC ELECTRIC POTENTIAL RESULTS AT KEW 
in the 10th edition of the ‘ Encyclopaedia Britannica,’ I expressed each hourly value 
in a diurnal inequality as a percentage of the mean value for the day. 
The principal maximum and minimum, for example, in Everett’s mean diurnal 
inequality for the year at Kew were given as 139 and 71, and thence the range 
would be 68. In an important and very comprehensive paper, # Mr. A. B. Chauveau 
has employed a method of representing the ranges which differs from the above only 
in taking the mean of the 24 hourly values as 1 instead of 100. He compares in 
particular what he calls day and night ranges (amplitude cliurne, amplitude nocturne). 
For both ranges he takes the late evening maximum, so that 
amplitude diurne = night maximum less afternoon minimum, 
amplitude nocturne = night maximum less early morning minimum. 
He did so because in all the cases he considered, with the single exception of Lyons, 
the evening maximum exceeded the forenoon maximum throughout the year. 
Finding that at most places the diurnal inequality was nearly the same for May, 
June, July and August, Chauveau obtains “ summer ” values for his day and night 
ranges from a diurnal inequality based on days selected from these four months. 
For corresponding winter values he usually confines himself to days selected from 
December and January only. In dealing, however, with the Bureau Central 
Meteorologique in Paris—the station which he considers most fully—his winter 
includes as well days from late November and early February. Chauveau also 
records the ratio borne by the mean value of P from the selected winter days to the 
corresponding summer value. In most cases he confines himself to fine weather 
days. 
Table VII. summarises the chief results given by Chauveau, with the addition 
of corresponding results for Kew from Tables I and III. 
Chauveau apparently regards the conditions at the Bureau Central as having 
somewhat deteriorated since 1893 through the growth of trees. As against this, 
the data there for 1893-4 depend on a somewhat limited number of days, and any 
single year may not be fully representative. The site at Perpignan is considered by 
Chauveau amongst the best. As to Kew and Greenwfich, I shall quote Chauveau’s 
own words ( loc . cit. p. C 52). “ La modification progressive de la variation d’ete 
dans les observations de M. Everett, de M. Whipple et dans celles de Greenwich 
nous parait etre en rapport avec des conditions de moins en moins bonnes dans 
f installation du collecteur.” 
The results at Greenwich and at the College de France show a rather striking 
similarity which Chauveau notes, but he regards them both as abnormal in several 
respects. 
A mean from the two sets of results for the Bureau Central presents fairly similar 
* ‘Annales du Bureau Central Meteorologique de France,’ Annee, 1900, I Memoires, pp. C 1 to C 120. 
