

¥ 
ON ELECTRICAL OBSERVATIONS AT KEW. 199 
both instances the cloudiness and humidity precede the electricity, and strongly 
indicate that whatever relation may exist between the development of positive 
electricity and humidity on the one hand, and that of negative electricity and 
cloudiness on the other, such relations are not only likely to be of a very 
constant character, but that a similarity exists between the two sets of phe- 
nomena which goes far to show that the nature of their connexion, if any, 
~is also similar ; the one, viz. positive, principally indicating, as we have before 
remarked, the electric tension of aqueous vapour; the other, viz. negative, 
the electrical disturbances produced by the sudden precipitation of this vapour 
when existing as cloud. 
It would greatly contribute to our knowledge of this part of our inquiry, 
ifsystematic and comparative observations were instituted at different observa- 
tories, on occasions of electrical disturbances, of a somewhat similar character, 
but of course considerably varied in their details, to those adopted on the oc- 
easions of magnetic disturbances. A principal feature in such observations 
should be ¢he observation of the electrometers at regular but small intervals of 
time during the continuance of the disturbance, so that curves of the variations 
of the instruments might be readily projected at any time afterwards.  Pro- 
vision should also be made for noting the precise instants at which particular 
and striking phenomena occurred, such as lightning, thunder, a change in the 
hind of electricity, the commencement of rain, the commencement of heavy rain, 
the termination of rain either light or heavy, also the same phenomena as re- 
gards hail or snow. A rain-gauge should also be kept for these particular 
phenomena ; it should be of such a construction as to admit of its being fre- 
quently read during the continuance of the disturbance; and its indications 
should be noted at sufficiently short intervals to afford data from which a 
curve could be constructed by which the eye could readily judge of the light- 
ness or heaviness of the rain by the amount precipitated within the interval 
fixed on. Observations of the kind just alluded to should by no means be 
confined to the more striking exhibition of electrical phenomena, such as 
thunder-storms, &c., but upon the slightest.indication of a disturbance they 
should be immediately resorted to; even on the positive tensions ranging 
higher than usual, the shorter intervals of observation may with great pro- 
priety be adopted, if it should be only for the purpose of securing on such 
extraordinary occasions the epoch of maximum; and in all instances that it 
may be deemed advisable to resort to them, they should be continued while 
there is the least indication, either from the appearance of the sky or from 
- the instruments, of the existence of the disturbance, and in fact until the ob- 
server is perfectly satisfied that it has ceased. It may be well to remark, that 
electrical disturbances appear to be very confined in their effects, extending 
over but a comparatively small portion of the earth’s surface. 


Mr. Matters Report On the Facts of Earthquakes does not appear, as in- 
tended, in the present Volume, in consequence of the manuscript having been 
delayed by the author, pending his researches in foreign libraries, until too 
late for the period fixed for publication. 
The Report will appear in the Volume for next year. 
