. 804 
the Mecanique Celefe of M. de Laplace, 
which treats of the fatellites, the comets, 
the refractions, the inequalities of Fupiter, 
Saturn, and the Mocn, and contains on 
each fubjeéct the utmott efforts of theory, 
and the higheft degree of perfeétion. 
The av:hor gives new refults relative to 
the maffes of the planets; and he has re- 
cently confirmed them by the calculation 
of an anciert Chinefe obfervation of the 
obliquity of the ecliptic made 1100 years 
before the vulgar era, which gives 23° 54’, 
whereas he finds 52’ by his Theory, 
(tom. LIL. 1 VI. ch. 16}; another, 100 
yerrs before our era, gives 229 45°, 
Whereas it is only 44’ by the Theory, 
which eonfrms the mafs of Venus inade 
ufe of by M. de Laplace, aud the dimi- 
notion of the obliquiy of the ecliptic by 
52" annually, though many obfeivations 
appeared to give only 36”. 
We have received the book which con- 
tains an account of the operations under- 
taken in Lapland, to determine an arc of 
the meridian, in 1802, by Meffrs. Ofver- 
Bom, Swanberg, Holmquift, and Palan- 
der, 196 pages, Svo. They made ufe of 
the new decimal meafures, as all thofe 
ought todo who take an intereft in the 
progrefs of reafon. 
The refult, p. 187, is, that the degree, 
the middle of which falls at 66° 20’, is 
EII,477,4 metres, Or 57,196,2 toifes; | 
but to make this reduction, they have 
fuppoled the metre 443" 2,959, as did the 
eommiffioners of weights and meafures in 
Franee; and for this purpofe they. have 
taken the metre at the freezing potnt, and 
the toife at 13° of the thermometer of 
0%. In my opinion it is more natural 
to take them both at the mean tempera- 
ture which is 93°. By the average of 
feveral years’ ob!ervations, it is the zero 
of my new thermometer: it is therefore 
neeeffary to take o! c64. from the metre, 
and add o'# 046 to the toile, according to 
the experiments made by Lavoifier, and 
in which FE was concerned in 17823 and 
to make the following flatement: 8633954: 
448,369 :: 854, tothe metre. By this 
methed it is found to be 443" 435, inftead 
of 296. Ft is by this ftandard that I fhall 
regulate all the meafures of my altro- 
nomy, a: I informed the Inftiiute on the 
28th of Oétober. Hence I find that 152 
metres muft be deduéted from the number 
given above, and that the degree 1s 
575200. 
The degree of +736 having been mea- 
fared at 15°, three toiles muit be added 
to it; that of r802 having been mea- 
fured at 3° but reduced to zero, 8 toifes 
4 
Eiifiory of Aftronomy, by Lalande. 
[July 1, 
muft be deducted from it; this augments 
the difference by 8 toifes. The firft, in- 
ftead of 57,419, becomes 57,422; and 
the fecond, reduced to 111,462 metres, 
makes 57,200 toifes, fo that there are 
222 toiles over. As this correfponds 
with the other degrees meafured, and by 
the flattening produced by the pendulum, 
and the parallax of the moon, we cannot 
forbear adopting the new refult, though 
it is difficult to. comprehend how our aca- 
demicians could have fallen into fuch a 
greaterrorin 1736. The Swedes thought 
that the fextant of 9 feet was more ealily 
deranged and lefs fure than the repeating 
circle which they made ufé of. 
M. de Zach has examined the perform- 
ance of the Swedifh aftronomers; he has 
compared the angles and the reductions 3 
he thi:ks there are fome inaccuracies in 
it, but the work is neverthelefs very good 
and very important. 
To explain the enormous difference 
which there is between the meafure of the 
Swedes and that of the French, I obferve 
four things. 
1. The latter did not turn back the 
fextant, which would have been too difi- 
cult. 
2. The wire was fufpended by a ring on 
a thickifh cylinder, and it might have 
rubbed. 
3. They were not then aware how im- 
portant itis that the optical axis of the 
telefcope fhould be parallel to the plane ; 
two lines of difference in the pofition of 
the glafics, make fix minutes on a radius: 
of 9g feet, and it is poffible that this dif- 
ference may exift; hence in the diitance 
to the zenith an error fo much the greater 
might refult, as the telefcope was proba- 
bly directed to the ftars at their paflage 
of the meridian, and not at the wire me- 
ridian. 
4- I very well remember that Mavper- 
tuis told me he had a great inclination to 
begin the meafure again. 
We have likewife {een in the Tranfac- 
tions ‘of the Royal Society of London, 
that Mucge has meafured three degrees 
in England. He has found 111,189 me- 
tres at 52°, which agrees with the meas 
fures of France ; but he has found in the 
northern part 164 metres lefs than in the 
fouthern part, where he ought to have ~ 
found 23 metres more: this announces — 
irregularities in the interior ftru€ture of 
the earth, and in the attraétions of the 
mountains, which make us-defirous of 
having the meafure of degrees of longi- 
tude, which will not be affected by thefe 
irrezularities, 
M. de 
