

TRANSACTIONS OF THE SECTIONS. 13 
elevated at any height above the surface, the instrument on being lowered gives 
signs of negative electricity, while on being raised it will indicate positive. When 
the operation is thus performed, this change of sign must be taken into consideration, 
in order not to attribute a contrary electricity to the atmosphere. In like manner 
a negative tension of the atmosphere is indicated, when the instrument after de- 
scending into the cabinet gives a positive sign.” 
The proportional forces corresponding to the marked degrees of Peltier’s electro- 
meter may be ascertained in two ways. Peltier has given a table, in which the equi- 
valent degrees were determined by an electric torsion-balance ; but the method 
employedj by Quetelet is more easily applicable, and gives very satisfactory and 
comparable results. This method, which is that of Volta, consists in dividing the 
electric charges-by placing spheres of the same diameter in contact. He took 
two electrometers, each surmounted by a metallic ball of the same diameter; he 
‘commenced by charging the first electrometer so that the needle indicated 74°°5, 
the two balls were then placed in contact to divide the charge. After this first 
operation the electrometer indicated only 70°. Their values, according to Peltier’s 
table, correspond to 2825° and 1400° of the torsion-balance, which corresponds 
almost exactly with the ratio of 2:1. After having discharged the second electro- 
_meter, he again placed it in contact with the first, which this time only indi- 
cated 64°, or 795° of the table of equivalents, which is nearly half of the number 
1400. This operation was repeated several times in succession in order to form 
the table. 
A regular and uninterrupted series of observations has been made with this in- 
strument by M. Quetelet at the Royal Observatory in Brussels since the beginning 
of August 1844. He has recently published these observations, extending through 
four and a half years, from this date till the 31st of December 1848, and the con- 
sequences he has deduced from them are very satisfactory and important. I will 
briefly state the principal of these results, referring for more extended details to the 
last memoir he has published on the climate of Belgium *. 
The first object of M. Quetelet was to ascertain the relation that exists, under 
ordinary circumstances, between the different heights above the neutral point and 
the electric intensities. The experiments of Erman and Saussure had long since 
made known that electricity is not equally expanded in the atmosphere; that it is 
nearly of the same intensity in a horizontal stratum of air, and stronger in the 
upper strata. ‘The discussion of the numerous experiments made by M. Quetelet 
with respect to this point, shows that in a place in the neighbourhood of which 
there are no higher objects, the electric intensity of the air increases, starting from 
a determinate point, proportionally to the height. But it must be borne in mind 
that this law has only been verified with respect to heights not exceeding 16 feet. 
The observations, with the view of ascertaining the annual variations of atmo- 
_ spheric electricity, were made every day at about the hour of noon, commencing in 
August 1844. The results of each year are in complete concordance, and are as 
follows :—I1st. The atmospheric electricity, considered in a general manner, attains 
its maximum in January, and progressively decreases till the month of June, which 
presents a minimum of intensity; it augments during the following months till the 
end of the year. 2ndly. The maximum and the minimum of the year have for their 
respective values 605 and 47 ; so that the electricity in January is thirteen times 
more energetic than in the month of June. The mean value of the year is repre- 
sented by the values given by the months of March and November. 3rd. The 
absolute maxima and minima of each month follow a course precisely analogous to 
that of the monthly means ; the means of these extreme terms equally produce the 
annual variation, although in a less decided manner. 
In order to determine the intensity of the electricity of the air in its relations with 
the state of the sky, M. Quetelet separated, for each month of the year, the num- 
bers which referred to a sky entirely clouded, from those observed when the sky 
was serene, or rather presenting so few clouds that eight- or nine-tenths were at 
least entirely unclouded. In order not to complicate the results by foreign influ- 
ences, he omitted the observations made during storms, snow, rain and fogs. The 
table thus formed gave the following results:—Ist. Whatever be the state of the sky, 
* Annales de l’Observatoire Royale de Bruxelles, tom, vii. 1849. 
