FROM SELECTED DAYS DURING THE SEVEN YEARS 1898 TO 1904. 
315 
features to the latest Kew results, though both the day and night ranges appear to 
be larger at the former station. The Kew summer data are from the diurnal 
inequality in Table III. for the four summer months combined. If the quantities 
had been found for each of the months independently, the arithmetic means would 
have slightly exceeded the values in the table, viz., amplitude diurne (P54, amplitude 
nocturne 0'45. The Kew results for winter are arithmetic means from December, 
January and February treated independently. Omitting February, the values would 
be less, viz., amplitude diurne 0T4, amplitude nocturne (P35. 
As regards the different Kew data, it should be taken into account that Birt’s 
were obtained with the old Donalds apparatus, the point at which the potential was 
measured being some 16 feet above the dome and more than 80 feet above the 
general level of the ground. Also the observations were from the even hours only, 
which inevitably leads to smaller ranges than when hourly observations are taken, 
Birt grouped his data in several classes. That taken by Chauveau included only 
low positive potentials, i.e., excluded all cases where the potential was negative or 
exceptionally high. Everett’s data included all readings positive or negative, 
Whipple’s all but days of negative potential. 
Table VII.—Abstract of Chauveau’s Results and Comparison. 
Place. 
Period. 
Mean 
length 
of tube. 
Metres. 
Amplitude diurne. 
Amplitude 
nocturne. 
Ratio of 
mean values 
of potential 
Winter. 
Summer. 
Winter. 
Summer. 
gradient. 
Winter/Summer. 
Lisbon . 
1884-7 
0-85 
0-28 
0-41 
0-87 
0-69 
— 
2-15 
Perpignan . 
1885-95 
1-5 
0-39 
0-38 
0-67 
0-46 
1-45 
Florence . 
1885 
1-75 
0-48 
0-46 
0-78 
0-61 
1-38 
Moncalieri. 
— 
— 
0-36 
0-47 
0-47 
0-40 
1-69 
Lyons. 
1885-90 
— 
0-16 
— 
0-36 
— 
2-14 
Parc St. Maur . . . 
1889-90 
— 
0-34 
0-65 
0-58 
0-52 
1-29 
College de France . . 
1885-7 
— 
0-23 
0-86 
0-42 
0-30 
2-00 
Eiffel Tower .... 
1893 
1-7 
— 
— 
— 
0-48 
55 J) .... 
1896-8 
0-55 
— 
_ 
0-37 
_ 
Bureau Central 1 
Meteorologique , | 
1893-4 
1-6 
0-16 
0-76 
0-40 
0-57 
2-01 
Bureau Central 1 
Meteorologique . f 
1894-9 
1-4 
0-21 
0-57 
0-56 
0-50 
1-53 
Kew . 
1845-8 
— 
0-09 
0-30 
0-49 
0-68 
1-27 
55 • • • • • * 
1862-4 
1-0 
0-54 
0-59 
0-92 
0-62 
1-75 
55 . 
1880 
1-3 
0 • 35 
0-75 
0-64 
0-54 
2-58 
55 . 
1898-1904 
1-3 
0-18 
0-52 
0-36 
0-44 
2-00 
Greenwich. 
1890-3 
1-8 
0-17 
0-80 
0-45 
0-28 
2-54 
§ 12. Chauveau also analyses the several sets of data for the diurnal inequalities 
at the Bureau Central and the Eiffel Tower in Fourier series. He takes five terms, 
one more than I have taken for Kew, and says that the additional, or 4’8-hour term, 
2 s 2 
