Ordnance Survey Astronomical Observations. 355 



" What great events do flow from little things," says an 

 old comic writer, but the few numbers above are a veritable 

 Pandora's box of trouble, likely to make every surveyor and 

 geodesist throughout the earth to tremble, when considering 

 the consequences which must certainly follow. That "nothing 

 was given to man without great labour," was a proverb in 

 the time of the Romans, and if true in ordinary matters, how 

 much more pointed and impressive does it become when push-? 

 ing scientific affairs to the utmost attainable degree of accu- 

 racy. To determine the latitude of a place to 30" is easy 

 enough; to 15", is not difficult; but to 1", the difficulty is 

 increased a thousand fold, nay, every property of Nature and 

 of matter seem to combine to prevent our discovering this 

 secret of the world. With a proposed accuracy of 1", still 

 more if 0"-l or 0" 01 be insisted on, an account must be 

 taken, and an explanation rendered of the above discord- 

 ances, preparatory to any hope of their being eliminated 

 from the determinations for latitude. 



It is easy to attribute the discrepances to " local attrac- 

 tion,'' but that is merely giving the difficulty a name ; and 

 the question still remains as to how a numerical correction 

 can be obtained. It is by no means the first time that such 

 a disturbing cause has been suspected, but previously obser- 

 vations have been conducted at so few stations, or have been 

 liable to such great uncertainties from error of observer 

 and instrument, that little attention has been paid to the 

 allegation. Actual mountains have however been generally al- 

 lowed to possess a sensible influence in this way ; and then the 

 observing places have usually been picked out at the greatest 

 practicable distance from such questionable neighbours. 



Such, we conclude, were the precautions taken with the 

 ordnance stations ; and certainly they are more numerous, 

 and better and more uniformly observed, we believe, than 

 any previous set that can be brought to bear on this ques- 

 tion. The probable error of observation is here so small as 

 for the time to disappear ; and yet there are discordances of 

 a greater amount than ever before known, and therefore 

 plainly and surely attributable to local attraction, whatever 

 that may be. The accusation, in fact, against mother earth 

 is fully proved, and must be proceeded with, 



