DEG 
meafuremeat, and for this perpofe procured large fires to be 
lighted, of thre teet diameter. When viewed through 
the telefeope of the quadrant, thefe are faid to have refem- 
bled in appearance fars of Fee third maguitude: the ey feemed 
however to fubterd an angle ef 5" inftead of 3” or 4", which 
they fhou'd have done by calculation ; from voice it was 1b- 
ferred that luminous bodies {c-setimes appear larger than 
By prececding in this Sait he foun 
triangles, the diflance m Malvoifne to 
rden, near Amiens, ta be 68,4303 ] and with a ze- 
nith feGtor of ro feet Tadius, he found the difterence of lati- 
’ ° } joc 
sy obferving the azimuth of the pole-far at its greateft 
| Bre eae at More 1, he determired the dire@ion ae a 
nace with the metidian3; an 
ihe fati ons to ne meridian, oe was 
evadled to complete the intercepted portions. 
patie thefe data he concluded a bani: in the latitude 49° 
o be 57,060 toifes. This refult differs very little from that 
ee ee Jater meafurements; yet this great precilion 
arofe, in re bgitike from a compenfation of errors. 
In ramids were erected at the extremities of 
the ie at ‘Vilejine and Juvefy, at the exact diftance of 
"| n a re-examination of Picard’s opera- 
one toife 
t fubte ails ne or that his ae had not been 
de termined with fufficient precifion. 
The fuccefs that a Picard’s meafurement, and the 
accuracy that trigonometrical operations were found to pof- 
fefs, determined the academy to extend his triangles ftill 
farther : the direction of the meridian both to the north 
and fout 
This was as partly carried into execution by Dominique Caf- 
as a bafe the diftance 
puriuits. 
~ Tt was not till the year 1700 that they refumed their la- 
bours. Caffini, aflifted by his fon Jaques Caffici, and Ma- 
raldi his nephew, continucd the feries of triangles as far as 
the neighbourhood of Perpignan, above 6° fouth of the ob- 
fervatory of Paris 
They traced a bafe of verification 4246 coifes, a little to 
the ealtward of ya eae the length of which, by direc 
eee rement, was found to agree ak exadtly with a de- 
uced by calculation on the triangles. 
The northern part of the arc fre om Paris . Dunkitk was 
not terminated tul the year 1718. The altronomers em- 
ployed on this occafion were Jaques Caf Maraldi, and 
De la Hire. They hikewife meafured a of ee 
in the vicinity of Dunkirk. When the tule of thefe ope- 
rations was examined, the fouthern degree was = cael 
to 57,097 toifes, and the northern 56,960. was thus 
that, after a period of 30 years from its cominencement, this 
great work was brought to a terminat 
The t, as far as it related to a use a of 
di ifferent eg ee. was certainly erroneous; but this we can- 
not be furprifed at, when we recollect the hpe ee flate of 
aftronomical inftruments at that period; but by thefe ope- 
rations the foundation for the improvement of the {cience of 
geography was laid. The advantage of combining aftrono- 
mical and trigonometrical obfervations was diltinily per- 
— and the project formed of 3 thefe triangles 
r the whole (iptaces of the kingdom. 
REE. 
e above mentioned operations began te derive an 
oer intereft, from a queftion of great importance that 
about that time engaged co attention of the {cientific world; 
this was the determination of the érve figure of the earth, 
Hitherto we have confidered the meafure of a degree as the 
ony baie fite ftep for determining the earth’s magnitude, 
u e fuppofition of its being perfe&ly ye reals in 
a prs all the degrees of latitude being equal, it is evi» 
dent that the meafure of one would have afforded fufficient 
ata - ey ting the value of the whole circumference. 
7. we define a degreeof themeridian to be that {pacewhich | 
we muft pafs over (in moving direétly north or fouth ), to pre» 
duce : oe in the vertical line equal to that quantity. We 
have France indicated 
a ®contery en ees a we cannot wonder that thofe, 
db oO 
e, tha tb 
who 
ory were cere 
foie figure at the 
poles ; on the other hand, it had fo happened, he i beft 
nown meafures at that time, indicated that the polar axis 
was the longeft. ‘Caffi propofed meafuring oad 
cally a degree of longitude, or, what was ftill preferable, 
degree of a a ee perpendicular to the meridian. Thi 
{cheme wa te carrie 
pened, ne the iste oe 
voured the idea that t 
geographical 
: for an arc perpendicular to the me- 
ingdom, gave to the geo- 
graphy of that country a precifion unknown i: ee other 
part of the world. 
1e cr eongnne eal peconiaiasl, 
even at that period, 
the e 
ors were occafioned chiefly by 
my coer - 
fince they are 
- 
oa 
.O 
rs) 
rey 
93 
ou. 
fay 
Bs 
we 
ww 
ct 
= 
rs) 
et 
ce 
a 
@ 
a 
or very near, quator, and 
imfele to “nace ne difficulties a haa of ahi enterprife. 
7 The 
