96 Olservalions on the Measurement of 



The latitude of Montjui, determined by a very long and 

 regular series of zenith distances, is full 3",24 less than 

 that deduced from a similar series of observations made at 

 Barcelona, with the very same instruments, and with equal 

 care. Moreover, there is reason to think, from other ob- 

 servations, tnat the latitude of Barcelona (which is sup- 

 posed to be 45") ought 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 have been the cause of this 

 irregularity; but then the latitude, as deduced from ob- 

 servations made at Barcelona, should have been less than 

 it appeared bv those made at Montjui itself; for the devia- 

 tion of the plumb-line (or of the spirit contained in a level) 

 could only be occasioned by the little chain of land elevated 

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

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

 tions arising from this source would be northward, the 

 zenith distance of circunipolar stars would be augmented 

 by that deviation, 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 43'''. 

 Hence it seen)s probable, that the cause of this irregularity 

 must be sought elsewhere, and that it is not likely to be 

 discovered without repeating over again the saiTie obser- 

 vations. 



Moreover it does not follow that the latitudes of two 

 places are correct, because the declinations of the stars de- 

 duced from them correspond ; for the deviations caused by 

 local attractions, or from any other source, arc made to 

 disappear in correcting the declination, but remain uncor- 

 rected in the latitude of each. 



Lieut. Col. Mudge is also of opinion, that the irregularity 

 in the value of his degree may be ascribed to deviation of 

 the plumb-line, occasioned by local attractions. This is cer- 

 tainly very possible, and may be decided by an examination 

 of all circunutances on the spot. But if there be really 

 an error of \" in the extent of the whole arc, this should 

 rather be ascribed to some defect in the observations them- 

 selves, than to any extianeous source ; for the observations 

 of diflerent stars give results that difi'er m(»re than four se- 

 conds from each other. 



I shall now conclude this memoir, by expressing a wish, 

 which men of science in England have it more in their 



power 



I 



