^4 SCIENTIFIC ME-Vrs. 



latitude of Paris observecl at a ejiven period should appear, 

 in consequence ot an 0!*cilla ion then at iu maxim um, to(v 

 great by \'\ tlie errour btiii^ proportiouji to the cosine of 0; 

 the year following at the same time it would be proportional 

 only tothecosineof 350*, and soon, till at the end of 9 years it 

 would he nothinj?. At the end of 18 years h«iwever it v on Id be 

 1" in the or'posite direction, whence a diiference of 2" miijht 

 appear in the altitude ot ihe pole; but so small an inequa- 

 Arfonentt for }\ty in so long a period would not b^- noticed. To show the 

 ***^ probability of this we mi«ht say. that Bradiev, from a num- 



ber of observations of the polestar in 1753, found the lati* 

 tude of Greenwich 51* 2B' 41*5", though !romastill greater 

 number he had before found it only 51* 28' 38". We may 

 suppose therefore an osciliatioi of 2" with a short period; 

 or a greater oscillation, of which only a part h^s been ob- 

 served. The latitude of the observatory at Paris too was found 

 to be 48* 50' 10' at one time, and 48* 50' 14" at other 

 times, by Lacaille, Cagnoli^ Mechain, and myself. These 

 differences might be ascribed to oscillations of at least '4 '» 

 and a period of about 15 years, so that there would have 

 been 2^^ periods between Lacaille and Cagnoli, and one 

 But probably only between Cagnoli and us. But 1 must add, that, 

 there are none, jj^y-jjg examined at large the observations of Bradley for 

 five successive years, I have perceived no trace of these 

 oscillations ; that if there were one of 2 ", it might fre- 

 quently be confounded with the errours of observation; 

 and that the dirlereuce of 3*5 " between the two results of 

 Bradley might arise from his having changed his quadrant 

 in the interval, and particularly from the errour of colU- 

 naation, which for his old quadrant was 1'74'> and for the 

 other 8', not being known with suffjcieut precision, of 

 which there are many instances. Thus we may take it for 

 granted for the present with Mr. P. and astronomers in 

 general, that there is no oscillation, or a very minute one; 

 tboogh thi» but of this we have no deiiiODstialion, and it is a point of 

 remains to be fti:^fficieut importance, to be worth ascertaining with an in- 

 • * slrumeut, in which no errour in the collitnation is to be 



apprehended. For this itjw'ould be sufficient to. observe 

 for some years with Borda's circle the meridian alti- 

 tudes of the polestar above and bel^w the pole during 



the 



