y 
2 
. ON ELECTRICAL OBSERVATIONS AT KEW. 195 
diurnal period more or less in harmony with it. We have already remarked, 
that the record of negative exhibitions does not furnish us with sufficient 
data previous to 1845'to determine the diurnal period ; nevertheless a synop- 
tical arrangement of the hours included in the entries under the head “ Limits 
of Time,” furnishes us with an approximation to such a period—at least so far 
as the time of occurrence of negative charges is concerned. The following 
table, which is deduced immediately from Table XCII., exhibits the number 
of times negative charges (more or less) were observed between August 1843 
and December 1844, both inclusive, between the hours specified, making in 
the whole 231. 
TABLE XCV. 
Number of readings of negative electricity between the hours specified, 
from August 1843 to December 1844. 

Between 
g F g 
E afi]. 4 2 
aldigia|elelSiclaldidisialalela|4i= 
Sl alalaloltiz isl alalaiafajalalaisia 
© [es foo Jor | | fag | B18 [o> [ost te [0 fe [oO IIa 
B fees | fos |e |S |S] S les [acs [os [a fos Jo fea | le || B 
2D RD [ES JOD |S> |S Jr [0 [em [eH fad [0 [ES ]00 Jo [| 
1} 5 | 9 |11)10)11)22)21/21)17|23)22)14)12)13)10) 7 | 2 |231 
It appears from this table that during the seventeen months negative elec- 
tricity was not observed earlier than 5 a.M.: at the commencement of the 
series the numbers are small, but they increase gradually until 11 A.M., im- 
mediately after which hour they are doubled as compared with the preceding 
three hours. This value slightly decreases until between 2 and 3 P.Mm., and 
is again augmented between 3 and 4.p.m. A sudden diminution occurs be- 
tween 5 and6 p.m. The numbers from 5 P.M. to 8 p.m. are rather higher 
than those from 8 a.m. to 11 A.m., and Jate in the evening they are again 
few as at the commencement. The period of the day between 11 a.m. and 
5 P.M. is particularly characterized by the more frequent exhibition of ne- 
gative electricity than either the forenoon or evening, and the ratio as com- 
pared with these periods is very considerable. It is remarkable that so close 
a correspondence as regards the development of negative electricity in the 
middle of the day should obtain in the series of negative readings previous 
to 1845 and during the three succeeding years (see Table III. page 117). It 
is perfectly clear that the greatest number of negative readings occurs about 
the middle of the day, and this of itself would suggest the great probability 
of the existence of a diurnal period in the exhibition of negative electricity. 
TABLE XCVI. 
Mean amount of cloud at each observation-hour, Gottingen mean time, 
_ as deduced from the observations of six years at the Royal Observatory, 
Greenwich, and expressed in parts of the natural scale,—a sky completely 
covered with clouds being represented by 100. 
Mid.|2 a.m./4 a.m.|6 a,m./8 a.m,|10 a.m.|Noon.|2 p.m.|4 p.m.|6 p.m.|8 p.m.|10 p.m.| Mean. 

