2ach on Repeating Circles. 411 



earth, which we never had the slightest mtention of doing, 

 would have seen, if he liad read or understood our work, 

 which it appears he has not done, that such an instrument 

 was precisely and absolutely the one which it was necessary 

 to employ, since our principal object was to try whether such 

 an instrument would produce again the same phaenomena 

 which a similar instrument had exhibited at Barcelona. We 

 repeat, our project, and our intention in the operation which 

 we undertook and executed in die environs of Marseilles in 

 1810, had nothing to do with the determination of the density, 

 the magnitude, or the figure of the earth, nor of an invariable 

 and universal measure deduced liom that magnitude and 

 figure. These were the objects accomplished in France and 

 Spain with the instruments in cjuestion, which were also 

 thought quite sufficient for determining the deviation of plumb- 

 lines or of levels caused by the attraction of mountains. M. Me- 

 chain asserts this formally in the second volume of the Base 

 Metrique (p. 491): " We have taken advantage (says he) of 

 our abode at Perpignan, to make observations of latitude, in 

 the hope that they may serve to ascertain whether the attrac- 

 tion of the Pyrenees alters the meridional altitude of the stars 

 at Perpignan by causing a deviation of the plumb-line, or of 

 the level of these instruments towards the south, as has been 

 conjectured." We have seen above, that M. Delambre sus- 

 pected that an effect of 0"'65 might be exhibited by these in- 

 struments. He attributed the difference of three seconds 

 found between Barcelona and Montjouy to this same effect of 

 attraction ; and we, on the contrary, in our work U Attraction 

 des Montagnes (p. 359), said: " We have formerly declared, 

 that, so far from seeking the cause of these anomalies in local 

 attractions, or in the irregularities of the density of the strata 

 of the earth, we were much more inclined to lay the blame on 

 the instruments, and even on the observations." 



What then become of the censures and criticisms of this 

 celebrated artist ? Is it possible that he has dissertated de 

 land caprind ? But indeed, let us see whether it was so ab- 

 surd as this famous artist (whose opinion in these matters is 

 certainly of great weight) would make us believe, to have em- 

 ployed a small repeating circle in finding the effect of the at- 

 traction of mountains. 



Setting aside that the greatest astronomers and geometri- 

 cians of France had done the same thing as ourselves, and 

 hatl even gone beyond us, since they executed a work of the 

 highest and most extensive importance, and one which cost 

 the state millions ; instead of which our modest dwarfish ope- 

 ration was no expense to any Government whatever, and was 

 3 F 2 only 



