Ordnance Survey Astronomical Observations. 357 



are altogether powerless here ; and so we are driven to the 

 only remaining hypothesis, viz., vast caverns underneath the 

 surface of the earth in certain spots ; or, perhaps, immense 

 masses of rock or metal of much less, and in other places, of 

 much greater density and specific gravity, than the neigh- 

 bouring material. But whether holes or masses, or veins or 

 dikes, they must be something mighty in size, and by no 

 means very distant, to produce such great, but at the same 

 time, irregular, effects. 



These discordances too appearing so very generally in the case 

 before us, and acting of course on the longitude as well as 

 the latitude, must render uncertain the astronomical elements 

 of position of all places yet observed, by any instruments, in 

 other countries as well as this ; for in no place has any cor- 

 rection for local attraction, under as well as above the sur- 

 face, ever been applied, or indeed obtained, or attempted. 

 The multitudinous measures necessary for the purpose are 

 still to be made. 



Hitherto men have fancied, or at least appear by their 

 conduct, with the slight exception already noticed, to have 

 laid the flattering unction to their souls, that to determine 

 the true astronomical position of a spot, they had merely to 

 improve their instruments, and multiply their observations 

 of the stars. But now it is shewn that there is another cause 

 at work, which the above proceedings do not touch. In fact, 

 even if we had a perfect astronomical instrument, and if 

 angels were to observe with it, still the results would be in 

 error by the full amount of the " local attraction ;" and that 

 may be far too large to be passed quietly by. 



Our public observatories will not be affected by the anomaly, 

 so far as their researches in cosmical astronomy are con- 

 cerned; it will only be of importance in geographical as- 

 tronomy. But it will both greatly affect all existing 

 measures of arcs of the meridian, and greatly trouble the 

 mapmakers. How, for example, shall they draw the parallels 

 of latitude through Great Stirling and Cowhythe, when there 

 exists an anomaly there of 9"-5, equal to one inch on the 

 6-inch-to-a-mile maps ; and as yet there is nothing to 

 shew on which side of either place, or whereabouts in the 



