188 REPORT—1849, 
1555" p.m. It is worthy of remark, that the approach of the cloud to the 
zenith, the formation of the heavy rain-drops, and the affection of the instru- 
ments, the charge being negative, were apparently simultaneous, and succeeded 
by the sudden gusts of rain constituting the heavy squall. 
(*) May 18, 1844.—The contrast between the observations at Kew and 
Greenwich is interesting: it furnishes us with another instance (and perhaps 
the most striking of the three) of the affections of the instruments by the prox- 
imity of cloud, mest probably czrro-stratus, which was prevalent at Green- 
wich, at least before noon. During the changes that occurred there in the 
electrical charges, small quantities of sleet only fell, and these not in any de- 
gree measurable, for we find on May 18, 22 hours Gottingen time, the same 
records of the rain-gauges as on May 17, 22 hours; but at Kew the period 
marked by the affections of the instruments at Greenwich is characterized by 
three showers, two of which are recorded as heavy, the electrical changes 
being considerable. It is to be remarked, that at Greenwich the tension was 
higher than had been observed previously in the course of the year. These 
phzenomena appear to point to a common origin of the electricity noticed at 
the two observatories, viz. the presence of a particular kind of cloud. It 
cannot in this instance at least be immediately connected with the rain, for 
although the changes were manifested at Kew during the continuance of the 
showers, yet electricity of a greater tension than any that had been observed 
during the former part of the year was recorded at Greenwich ; the same ac- 
tion was going on at Greenwich without the rain us at Kew with it: the only 
difference appears to have been, the absence at Greenwich of those particular 
conditions necessary to the production of the sudden gush of rain most fre- 
quently characterizing the exhibition of negative electricity, or rather the 
oscillation of the electrical condition between positive and negative. The 
instance before us presents a very instructive comparison with the passage of 
the cloud over the Kew Observatory on September 10, 1843, when the con- 
ditions for the production of rain did not appear to have existed at Kew, 
while they did at Greenwich ; yet the electrical instruments at Kew were 
affected, while those at Greenwich were not. 
(‘) June 10, 1844.—The records of this shower at both observatories were 
as under :-— 
Kew. 
Previous to the fali of any rain upon the conductor, the Henley rose to 
90° pos., sparks 112 inch*. At one time of this high positive charge (before 
the rain), the Leyden jar, of about 56 square inches coating, on being applied 
to the conductor, became charged to the intensity of the rod in about 20 
seconds. The charge changed to negative shortly after the rain began, max. 
55° of the Henley, sparks #5 inch. These high signs lasted about a quarter 
of an hour, and spirtings occurred from the little ball above the discharger. 
The negative charge remained a considerable time after the rain had ceased, 
gradually diminishing. ee 
Nothing remarkable in the appearance of the clouds; they were rather 
fleecy or plumose, and not low, but large. 
* These were the longest sparks which we have yet observed; but on the 31st of January 
the continuous stream of fire from the conductor to the discharger was much more lasting. 
If the ball attached to the conductor and above the discharger were placed nearer or at the 
end of the cross-arm, the sparks would be longer; also if it were smaller. But it is, I fear, 
in vain to attempt to measure these very high tensions accurately by ordinary electrometers 
and dischargers. Our Henley was in this instance evidently useless. The shock of the 
spark reached the elbow without a jar. [Observer at Kew.] 
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