
ON ELECTRICAL OBSERVATIONS AT KEW. 189 
GREENWICH. 
June 104 25 Gottingen time, 1" 20™ Greenwich time. Cumuli, cumulo- 
strati, and dark scud; within the last three minutes the temperature has fallen 
3°, the reading just before the observation having been 745, and there was 
a sudden exhibition of negative electricity ; a large dark cloud was at the 
time passing over from the N.W.: at 1"27™ p.m. a fine shower of rain began 
falling ; at 12 29™ the temperature was 62°-0; and at 1" 46™ it was 59%5. 
Negative electricity recorded between 1" 16™and 1" 44™ p.m., max. tension 
20° Volta (2). Wind W., force 0 to 1 lb., rain falling. 
By means of these records we obtain a further insight into the conditions 
necessary for the exhibition of the phenomena detailed. Cloud being the 
origin of the electrical oscillations, appears very evident from the affections 
of the instruments at Kew previous to the fall of any rain upon the conductor ; 
and the very high charge communicated to the conductor under these cir-. 
cumstances is highly instructive. The usual march of the electrical tension 
was evidently disturbed by the approach of the cloud, although it exhibited 
nothing remarkable. This disturbance did not manifest itself at Greenwich 
until the cessation of the rain at Kew. It appears that at this time the ob- 
server at Greenwich noticed a large dark cloud passing over from the north- 
west, which was attended by two very remarkable phenomena :—a sudden 
diminution of temperature, with as sudden an exhibition of negative electricity. 
This appears to have occurred at least seven minutes before the fall of any rain. 
The presence of the cloud, the diminution of temperature, and the exhibi- 
tion of negative electricity, appear to ve closely and intimately connected, 
and to indicate either that the cloud itself underwent a remarkable physical 
change, which materially influenced bodies in its vicinity ; or, which is the 
most probable, that it existed in such a condition as to produce great physical 
changes in such bodies, so far as electricity is concerned. It is easy to con- 
ceive, that if by any means the temperature of the cloud should be diminished ; 
by coming into a colder portion of air, for instance, a sudden agglomeration 
of its vapour-particles might take place; its electrical ¢ondition be suddenly 
and extensively disturbed by the enormous tension which these newly formed 
rain-drops might acquire in consequence of the rapidity of their formation, 
in some cases the diminution of temperature being so great as actually to 
Sreeze them and thus produce hail, which at some seasons is not an unfrequent 
phenomenon accompanying the exhibitions of negative electricity. The 
electrical influence of the cloud thus circumstanced may not be confined to 
the mere strip of country over which the rain or hail may fall, but may ex- 
tend to some little distance beyond its circumference, and thus the signs may 
be changed without the actual fall of rain in such localities, or the negative 
State continue after the precipitating portion has left the place of observa- 
tion. Nor does it follow that rain must necessarily fall from every portion 
of the under-surface of a cloud; there may be an axis characterized by the 
lowest temperature ; around this may exist a zone having a higher tempera- 
ture, and another still higher, the skirts exhibiting the hzghest. 
It is well known that in showery weather the masses of cumulus present 
the appearance of highly heaped or vastly piled-up clouds towering high in 
the atmosphere, and on many occasions these cumular bodies are surmounted 
by sheets of cirro-stratus, through which their summits frequently penetrate, 
giving rise to that modification of cloud termed by meteorologists cumulo- 
stratus. By carefully noticing their mode of formation the idea will be sug- 
gested of vapour rising from the earth by evaporation with considerable force, 
