Proceedings of the Royal Institution. 385 



—and finally of contributing to the deteraiination of the size and figure 

 of the earth. Though their ultimate objects are, however, very different, 

 the connection between these two branches is intimate ; the basis 

 of both being a triangulation, connecting the principal points of the 

 kingdom, and proceeding from one measured base ; the only differ- 

 ence being, that a degree of accuracy is necessary when the objects 

 of science are contemplated, which, in the other case, would be a use- 

 less waste of labour and ingenuity. 



^^j^^he survey of Ireland, begun in 1825, in consequence of an appli- 

 cation from Parliament to the government, embraced both these 

 objects ; the principal one undoubtedly, a new valuation of the land 

 for the purpose of equalizing ihe distribution of the taxes levied by 

 the Grand Juries ; but at the same time the interests of science were 

 not overlooked, and it was recommended that this survey should be 

 executed in a manner that might conduce to the advancement of 

 science, and be creditable to the reputation of the country. The 

 Duke of Wellington, at that time Master General of the Ordnance, 

 selected Colonel Colby of the royal engineers, to carry the wishes of 

 Parliament into effect, and placed at his disposal liberal means for 

 executing this important work. 



The period at which attention began more particularly to be turned 



J towards the figure of the earth, may be dated about the end of the 

 17th century. Richer, a French academician, who had been sent to 

 Cayenne in 1762, to make some astronomical observations, was 

 struck with the singular fact, that his clock, which had been regu- 



j lated to meantime at Paris, had altered its rate, and lost 2 J' per day. 

 He determined the length of the seconds pendulum at Cayenne, and 

 found the opposite effect on returning to Paris ; hence he inferred, 



,^.,^j^^^ t|ie force of gravity was different at different places on the 

 earth's surface. Much controversy was excited by this discovery ; 



, , some doubted the fact, others denied the explanation, while many 



i, . attributed it to errors of observation. But Newton shewed that this 

 effect was a necessary consequence of the figure of the earth, pro- 

 duced by rotation on its axis, combined with the principle of gravi- 

 tation. And though the problem of the figure of the earth, deduced 

 fxqra .the laws of equilibrium, transcended at that time the powers of 

 aiialysis, his unrivalled sagacity enabled him in this, as in many 



