128 REPORT—1849. 
rather fleecy, roundish and somewhat detached. Wind N.E. and E,, its force 
about 500 grms. Daniell’s hygrometer marked 20° of dryness.” 
At sunrise the electric tension was registered at 65 div. Volta No.1. From 
this it appears that a tension of 65 div. at sunrise is considered as high for 
serene weather, and it might be inferred that tensions of a higher value indi- 
eated some other exciting cause than that which we contemplate as exciting 
the electricity of serene weather. 
In the explanations and remarks concerning the Journal, &c. at Kew, pub- 
lished in the Report for 1844, p. 130, a serene day is defined as follows: ‘In 
the column N is pointed out (by the letter S) such days as generally occur 
when the positive charge rises after sunrise, falls early in the afternoon, and 
rises again in the evening, accompanied by what is commonly understood by 
the term ‘fine weather ; but there are exceptions to this (rather vague) de- 
finition, which I believe require some habit, and an acquaintance with the 
observations of Monier and others, particularly Beccaria, to appreciate.” 
By glancing at the curves on pages 119 and 122, to which attention has been 
solicited, it will be seen that the movements, as deduced from the observa- 
tions in individual years and seasons, as well as those from the entire number 
during the three years, are perfectly in accordance with the movements in 
serene weather, and it is only the restriction to which allusion has been made 
that suggests the probability of the higher tensions being due to a different 
exciting cause than that of tne electricity of serene weather. In searching 
for such a cause among the records preserved in the Journal, we are struck 
with the fact, that in the majority of cases high tensions (7. e. those measured 
by Henley’s electrometer) are accompanied by fog; and this suggests that it 
is not improbable that these high tensions may be more or less direct mea- 
sures of the electricity, not of the atmosphere, but of the condensed aqueous 
vapour enveloping the collecting lanthorn. Of course the atmospheric 
electricity, as contradistinguished from that of the condensed aqueous vapour, 
will be mixed with it, and the conductor will be charged from two different 
sources, the atmospheric electricity exhibiting by far the smallest amount, 
and in cases of high charges forming probably but a very small proportion 
of the whole. There does not appear to be any direct means of separating 
these tensions ; for if we take the high numbers, a small proportion, as we 
have already said, must appertain to “atmospheric electricity ;” and if we 
take the Jow numbers as giving a more accurate measure of this element, on 
some occasions and especially at certain hours, the tensions exhibited may 
be those produced by the presence of aqueous vapour either in an invisible 
or condensed state, so that a degree of uncertainty as to the ¢rue forms of 
either of these diurnal curves must necessarily exist. Again, it is difficult to 
determine the point at which to separate the high from the low tensions ; the 
uncertainty attendant on the readings of Henley’s electrometer, combined 
with the electricity which alone is susceptible of exact measurement, tends 
greatly to place all readings of Henley’s instrument in the category of high 
tensions. As a first attempt to separate the high from the low tensions, 1° 
of Henley equal to 100 div. of Volta No. 1 was regarded as the separating 
point; but it soon became apparent that readings lower than 100 div. had an 
equal claim to be regarded as high, indications being afforded that they were 
measures rather of the electricity of aqueous vapour than of the atmosphere, 
The observations of three or four months were discussed in this manner, but 
the curves of low tension presenting very anomalous characters, the mean 
readings increasing very considerably towards 8 p.m. led to their abandon- 
ment, and other separating points were tried from 50 div. and upwards. The 
result has been that the point 60 diy. has heen employed in the further discus- 

