IIGURE OF THE EARTH. Q5 



Pantheon wholly inadmissible. It is, however, too true, that 



such errors are possible, and it is only by careful perseverance, 



and by repeated verification, that they are to be discovered and 



removed, as we have seen to be highly probable with respect to 



the station at Arbury Hill. 



But the same celebrated observer, M. Mechain, who handled J nstance ?J . 



* ' irregularity m 



instruments with great delicacy, and was possessed of peculiar observing the 



talents for this species of observation, has given us an instance < ll ff ereric * of 



of singular irregularity in the observations made at Montjui and 



at Barcelona. 



The latitude of Montjui, determined by a very long and 

 regular series of zenith distances, is full 324 less than that 

 deduced from a similar series of observations made at Barcelona, 

 with the very same instruments, and with equal care. More- 

 over, there is reason to think, from other observations, that between Bar- 

 the latitude of Barcelona (which is supposed to be 45") ought '^0™™* 

 to be diminished still one second, so that the difference between 

 the observations at Montjui and at Barcelona, will probably » 

 amount to as much as 4". Local attractions are supposed' to ascr ibedto Jo- 

 have been the cause of this irregularity j but then the latitude, cal attractions; 

 as deduced from observations made at Barcelona, should have 

 been less than it appeared by those made at Montjui itself; for 

 the deviation of the plumb-line (or of the spirit contained in a 

 level) could only be occasioned by the little chain of land ele- 

 vated to 120 or 130 toises, which passes to the north of Barce- 

 lona in a north-easterly direction. Now since the deviations . 

 arising from this source would be northward, the zenith dis- t ; ons are f a " 

 tance of circumpolar stars would be augmented by that devia- contrary na- 

 tion, and consequently the latitude deduced therefrom would 

 be diminished by just so much. But here the contrary occurs ; 

 for the latitude of Montjui deduced from the observations at 

 Barcelona is 48,23, whilst that obtained by direct observations 

 at Montjui is only 45". Hence it seems probable, that the 

 cause of this irregularity must be sought elsewhere, and that it 

 is not likely to be discovered without repeating over again th« 

 same observations. 



Moreover it does not follow that the latitudes of two places 

 are correct, because the declinations of the stars deduced from 

 them correspond j for the deviations caused by local attrac- 

 tions, or from any other source, are made to disappear in cor- 

 recting 



