828 Mr Sang on Optimum Surveying, 



it : riot from a passable acquaintance with elementary trigono- 

 metry, but from a profound and skilful application of its laws. 

 The interests of science are involved, and 1 imagine it to be 

 proper that a set of operations already of fifty-four years' stand- 

 ing, and as yet unproductive of a single definite and trust-worthy 

 result, should be thoroughly sifted. The errors which have 

 been pointed out by Tiarks, Beven, and Ivory, imperiously 

 call for inquiry. 



In the year 1822, Dr Tiarks discovered that the longtitude 

 of Falmouth is 4s. 4 (time) different from that given by the 

 surveyors ; and a short anonymous article, satirical in the high- 

 est degree, though unintentionally so, inserted in the Phil. 

 Mag., April 1824, ascribes the discrepancy — to what? to the 

 errors of the survey .'* by no means, but to an irregularity in 

 the figure of the earth ! The result of Dr Tiarks' examination 

 is this, that the rate of error is 1'' for every 4' of longitude ; 

 that is, in the length of a line an error of one part in two hun- 

 dred and forty ; and this attributed to an irregularity in the 

 figure of the earth ! 



In the number of the same Journal for August 1824, there 

 is an article by Mr Bevan, containing the following statement. 

 Altitude of mouth of fixed cannon at King's Arbur, or the 

 upper end of the base on Hounslow Heath. 



Feet. 

 As determined by Mr Bevan, .... 90^ 



Vol. i. page 173. Trig. Surv. . . . . 91 i 



266 118 



Vol. iii. page 307 132 



exhibiting a difference of 40 feet among the statements of the 

 surveyors, and this concerning one of the cardinal points of the 

 survey ; the upper end of the base line ! Does this not call 

 for inquiry ? 



In July 1828, Mr Ivory takes the matter up ; and with 

 what intention ? The result of the survey between Dunnose 

 and Clifton had been, that the earth is a prolate and not an 

 oblate spheroid. Another irregularity in the earth's form ! 

 Mr Ivory, however, clearly shews that an erroneous use of the 

 angles observed had led to this startling conclusion ; and, not 

 following the example of Dr Tiarks, scruples not to declare 



