Ree e+ 
’ 
ON ELECTRICAL OBSERVATIONS AT KEW. 177 
In the succeeding table, the great majority of instances in which negative 
electricity has been exhibited, are characterized by ¢wo very interesting 
features. At Kew one of these features has been the falling of rain, in most 
instances heavy ; and the other the great probability, from the almost con- 
stant record, at or near the same epochs at the Royal Observatory, Green- 
wich, of cirro-stratus, and occasionally cumulo-stratus, that these clouds 
have more or less not only accompanied, but contributed their quota to, 
the development of the electricity observed. On numerous occasions, cirro- 
stratus has been observed at Greenwich without the electrical instruments 
having been affected, and from this we may with great truth infer that cirro- 
stratus in its ordinary action does rot occasion a disturbance of the regular 
diurnal march of the electrical tension, Most probably it is only when the 
conditions exist for the precipitation of rain, especially when the rain is 
formed very rapidly and in great quantities, that the electrical condition of 
the cloud is disturbed, and the conduetor affected negatively. From the 
great constancy of the phenomena during a period of seventeen months, we 
are inclined to consider that to a certain extent they illustrate the remark 


relative to the production of lightning by rain, which occurs in the Report of 
the Committee of Physics, including Meteorology, approved by the Presi- 
dent and Council of the Royal Society, pages 46 and 47. In speaking of 
thunder-storms, the writer, in alluding to one point to which the Committee 
wished some attention to be paid, says, —“ It is the sudden gush of rain which 
is almost sure to succeed a violent detonation immediately over-head. Is this 
rain a cause or a consequence of the electric discharge? Opinion would seem 
to lean to the latter side, or rather, we are not aware that the former has 
been maintained or even suggested ; yet it is very defensible. In the sudden 
agglomeration of many minute and feebly electrified globules into one rain- 
_ drop, the quantity of electricity is increased in a greater proportion than the 
surface over which (according to the laws of electric distribution) it is spread. 
Its tension therefore is increased, and may attain the point when it is capable 
_ of separating from the drop to seek the surface of the cloud, or of the newly 
formed descending body of rain, which under such circumstances, and with 
electricity of such a tension, may be regarded as a conducting medium. 
Arrived at this surface, the tension for the same reason becomes enormous, 
and a flash escapes.” In immediate reference to this remark, we apprehend 
the observations do not so much indicate the actwal electric tension of the rain 
falling on the conductor, as the effect on the conductor of the electric disturb-. 
ance occasioned by the production of the rain; this disturbance principally 
influencing the cloud from which the rain is precipitated, and through the 
cloud influencing the earth and bodies in its immediate neighbourhood. We 
Shall have occasion again to refer to this subject in the Notes that are sub- 
~The exceptions to the general fact of heavy rain falling when the con- 
~ ductor has been negatively electrified are rare; only ten instances are re- 
corded during the seventeen months ; they are given in Table XCIII. p. 185; 
some of them are extremely interesting, and are calculated to throw great 
light on the subject to which we have just alluded: we shall notice them in 
; their proper places in the Notes that follow. 
