194 REPORT—1849. 
conductors were affected almost simultaneously. If the shower seen at Kew 
and the one that fell at Greenwich be the same, we have another instance of 
the cloud being the common origin of the electricity exhibited at the two 
observatories *. 

It has already been remarked, that one of the most prominent results of the 
arrangement constituting Table XCII. is the almost constant accompaniment 
of rain in a falling state when the conductor exhibits a negative charge, 
and it is to be particularly noticed that this is in striking contrast with the 
condition of the atmosphere surrounding the conductor when high charges of 
positive electricity are exhibited, the tension not being in a state of oscillation. 
In both cases the conductcr may be said to be surrounded by moisture, but 
the conditions of this moisture are extremely different. In the case of high 
positive tension such as we have described, the moisture is not in the liquid 
state ; and even if it may be said to be in contact with the surface of the con- 
ductor, yet it has not passed beyond the form in which it exists as cloud ; the 
conductor under such circumstances may be considered as penetrating the 
cloud ; and bringing to us the electricity of the cloud itself. In the case of 
falling rain, the conductor is situated below the cloud, the drops impinge on 
it, and it is evidently a matter of question whether its indications are those 
of the electricity of the rain, or of a state induced in the conductor by the 
proximity of the cloud. A note appended to the description of instruments 
at Kew (Report 1844, page 124), relative to Henley’s electrometer, appears 
to lead to the conclusion that the latter is the case :—“ The oscillations of 
the index between the 30th and 35th degrees, sometimes during a heavy 
shower, plainly show that the electricity of the conductor is washed off, as it 
were, as fast as brought.” By the electricity of the conductor being washed 
off, as it were, it would appear that the electric state induced in the con- 
ductor was momentarily conveyed from it by the falling rain. In connexion 
with this, we must bear in mind that all rain is not accompanied by negative 
electricity, nor on the other hand is the negative charge always accompanied 
by rain. In those instances in which negative electricity has been observed 
without rain, the state of the weather is printed in italics in Table XCII., and 
in such cases the presence of cloud alone has been the accompanying phe- 
nomenon at the Kew Observatery ; nevertheless on some of these occasions 
heavy rain has fallen at Greenwich. If therefore negative electricity should 
be, as it appears to be, connected with cloudiness, it ought to present a 
* Tt is a remarkable circumstance and one demanding further attention, that most of the 
thunder-storms recorded in the foregoing pages passed more or less to the north-west of the 
Royal Observatory at Greenwich. .We give the following as illustrative of this remark :— 
August 4, 1843....... N. and N.W. August 15, 1843. ...... N.E., S.E., N.W. 
June 10, 1844. ...... N.W. July 1, 1844,............ N.W., N., E. 
July 5, 1844.......... N.W. 


To these instances we may add that of the remarkable thunder-storm which passed over 
London on July 26, 1849. In the meteorological observations furnished by the Astronomer 
Royal, and published in the weekly report of the Registrar-General, it is thus noticed :— 
“From 1" till 4" p.m. a violent thunder-storm, chiefly situated to the north; the flashes of 
lightning were vivid and in quick succession, followed by loud thunder at intervals of 15 to 
20 seconds generally.” The storm passed over London from §.W. to N.E., striking several 
buildings in its passage. During the continuance of the storm at Greenwich the electrical 
tension was strongly positive for a period of two hours and a half, viz. from 1" to 35 30™ while 
the storm raged in London; at other times, the observer writes, the tension was strongly ne- 
gative, with frequent constant volleys of sparks and galvanic currents. 
From the above it may be inferred that London is more particularly exposed to the effects 
of thunder-storms, most of them passing over the immediate neighbourhood of the metros 
polis, 


ae sa So 
WARES 
