150 
and Humboldt, all the elements of the _ 
magnetic theory of the globe, and he has 
given the requisite formule, im order to 
calculate what must be the inclination and 
the declination of the needle inany place 
whatever. ; 
The excursions made since that period 
by Messrs. Humboldt and Gay Lussac, 
into Italy, France, and Germany have 
furnished them with frequent opportuni- 
ties of comparing their observations with 
the mathematical hypothesis of M. Biot.. 
The difficulty of determining the meri- 
dian of the place has prevented them 
from observing the declination of the 
needle in their various stations ; but they 
observed the inclination, and the number 
of oscillations, which were made in a 
given time, by a horizontal needle, and 
have reckoned by a simple formula 
the number of oscillations that it would 
make in its true direction, and from hence 
the intensity of its magnetical force. 
In order to exhibit a connected view 
of their labours, and the consequences 
deducible from them, M. Gay Lussac, 
to whom was entrusted the care of their 
arrangement, has given a tabular view of 
the terrestrial longitude and latitude of 
the place; the longitudes and latitades 
im relation to the magnetical equator in 
the hypothesis of M. Biot; the inclina- 
tions calculated according to this hypo- 
thesis, and the differences that are found 
between observation and these calcula- 
tions; inshort,to render this table as 
perfect as possible, he has subjoined to 
it observations on the nature of the soil, 
and its elevation above the level of the 
sea. 
It is worthy of remark, that all the dif- 
ferences are of the same nature, that 
the inclinations, as they have been cal- 
culated, give too great quantities, which 
vary from $° 42’ to 5° 9’. Now if we 
even admit that some of these differences 
must be attributable to local circum- 
stance, or to the unavoidable errors of 
observation, it nevertheless appears highly 
probable, that the greatest number of 
them proceeds from the position assigned 
to the nodes of the magnetical equator, 
and to the angle which it makes with 
the terrestrial equator. 
It will be easy to ascertain what correc- 
tions the hypothesis of M. Biot will re- 
quire, in order. to represent more accu- 
rately the new observations, and to re- 
concile them with those an which he had 
determined his first elements. It is to 
be presumed, that M. Bict himself will 
find this object sufiiciently interesting to 
Proceedings of Learned Societies. 
[March 7, 
occupy his attention again, when he shall 
_have terminated the important and diffi- 
cult mission in which he is at present 
employed*. With the view of giving to 
this theory all-the precision of which it 
is susceptible, it is much to be wished, 
that a series cf observations were made at 
the most distant parts of the globe, with 
the same care and accuracy, as those of 
Messrs. Humboldt and Gay Lussac; but 
in the mean time it is sufficiently evident, 
that the intensity of the magnetical force 
is in proportion to the latitude, as M. 
Humboldt formerly remarked in his voy- 
age. Thus at Berlin it is 18703, while at 
Rome itis only 12642. It is likewise de- 
monstrated from. these researches, that 
the chain of the Alps produces a very tri- 
fling, if any influence; that of Vesuvius 
since the earthquake and eruption of 
1805, has not been much more sensible, 
and it appears to be attributable to local 
circumstances rather than to a particular 
magnetical centre, 
The description of the instruments 
they employed,.and the discussions mto 
which M. Gay Lussac enters respecting 
the best method of conducting such ob- 
servations, cannot fail to add to the con- 
fidence which the well knowa accuracy, 
and ability cf these indefatigable ob- 
servers naturally inspire. 
Messrs. Humboldt and Gay Lussac, 
the reporter proceeds to inform us, from 
eudiometrical experiments, and the ana- 
lysis of air, were led fo suspect, that all 
gaseous bodies have the same capacity 
for caloric. This consequence, ‘which 
appeared to flow from their observations, 
deserved to be examined more acurately, 
and Gay Lussac with this view entered 
on a series of experiments on returning 
from his journey into France, Germany, 
and Italy along with M. Humboldt. 
These experiments, while they confirmed 
the former, led, however, to a very oppo- 
site conclusion, Thegases, he had exa~- 
mined in conjunction with M. Humboldt, 
certainly possessed nearly the same ca~ 
pacities for caloric, but it would have 
been improper from this circumstance to 
have attributed the same property to all 
cases. without distinction. 
* Messrs. Biot and Arago had set out in 
September, in order to prolong the meridian to 
the Balearic isles, and to continue the labours 
which were interrupted by the death of - 
M. Mechain; in December they had begun 
the ebservations of the great triangle, which 
will join the isle of Ivica to the shorts of the 
kingdom of Valencia, sill 
